Tesis sobre el tema "Terahertz pulses"
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1
Koroliov, Anton. "Semiconductor characterization by terahertz radiation pulses". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2014. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2014~D_20140922_141151-18493.
Resumen
The goal of this dissertation work was to develop pulsed terahertz radiation techniques and use them to study different properties of the semiconductor materials and semiconductor devices. Three groups of materials were investigated: GaAsBi, GaAs nanowires, copper-indium chalcogenide. The used techniques are THz-TDS, optical pump – THZ probe, optical pump – optical probe and THz excitation spectral measurements. The main results that were presented in this dissertation are the following: thermal annealing has resulted in the shortening of electron lifetime in GaAsBi to picosecond values, which is important achievement for the application of this material in THz range components. In GaAsBi layers with larger than 10% Bi content absorption bleaching recovering on the picosecond time scale and its saturation can be realized when the wavelengths of the optical signals are as long as 1600 nm. The results of these studies can be applied in the production of SESAM with bismide absorption layer. The samples with GaAs nanowires emit THz radiation several times better than the bulk GaAs substrates due to enhanced light absorption because of localized surface plasmon resonances in GaAs nanowires. THz emission efficiency from thin copper-indium chalcogenide layers strongly depends on their stoichiometry and on the parameters of the top transparent contact layers, thus it can be used for the mapping of built-in electric fields in solar cells made from these layers.Šio darbo tikslas buvo susipažinti su terahercinių impulsų generavimo ir detektavimo būdais, įsisavinti įvairias terahercinių impulsų panaudojimo metodikas bei pritaikyti jas puslaidininkių medžiagų ir puslaidininkinių prietaisų tyrimui. Buvo tirtos trys medžiagų grupės: GaAsBi, GaAs nanovielutės ir Cu – In chalkogenidai. Tyrimui buvo naudojamos: THz – TDS, optinio žadinimo – THz zondavimo, optinio žadinimo – optinio zondavimo bei THz sužadinimo spektroskopijos metodikos. Pagrindiniai rezultatai aprašyti disertacijoje yra šie: GaAsBi bandinių atkaitinimas stipriai sumažino krūvininkų gyvavimo trukmes, kas yra naudinga THz komponentų gamyboj. Optinio praskaidrėjimo efektas ir pikosekundžių eilės krūvininkų gyvavimo trukmės GaAsBi epitaksiniuose sluoksniuose su 10% ir daugiau Bi atomų stebimas žadinant juos optine spinduliuote, kurios bangos ilgiai siekia iki 1600 nm. Šios GaAsBi bandinių savybės leidžia juos priakyti įsisotinančių sugėriklių veidrodžių gamyboje. Bandiniai su GaAs nanovielutėmis emituoja THz spinduliuotę kelis kartus geriau nei GaAs padėklas, dėl padidėjusios sugerties, kurią skatina paviršinių optinių plazmonų rezonansai GaAs nanovielutėse. THz emisijos efektyvumas iš Cu-In chalkogenidų sluoksnių stipriai priklauso nuo jų stechiometrijos ir viršutinio skaidraus kontakto parametrų, ir gali būti naudojamas saulės elementų, pagamintų šių sluoksnių pagrindu, vidinių elektrinių laukų tyrimui.
2
Carey, John Joseph. "Near field effects of terahertz pulses". Thesis, University of Strathclyde, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273433.
3
González, de Alaiza Martínez Pedro. "Generation of intense terahertz sources by ultrashort laser pulses". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS350/document.
Resumen
Le spectre électromagnétique possède une zone étroite, localisée entre les micro-ondes et l'infrarouge, appelée région des ondes térahertz (THz), qui est comprise entre 0.1 et 30 THz. Ces ondes, longtemps inaccessibles car situées à la frontière entre l'électronique et l'optique, connaissent aujourd'hui un intérêt grandissant et possèdent des applications prometteuses dans divers secteurs de la science comme l'imagerie médicale et l'identification des explosifs à distance. Cependant, la production de rayonnement THz intense, d'amplitude proche du GV/m, qui devrait permettre de sonder efficacement des matériaux à distance, reste encore une question en suspens. Cette thèse a précisément pour but d'étudier la génération d'un tel rayonnement THz par couplage de deux impulsions laser ultracourtes -une onde fondamentale et son harmonique deux- capables d'ioniser un gaz (par exemple, l'air ou l'argon). Le plasma ainsi créé joue le rôle de convertisseur nonlinéaire de fréquence, transformant une partie de l'énergie du champ laser dans la bande THz via une gamme riche de mécanismes physiques, notamment l'effet Kerr, la photoionization et les forces pondéromotrices induites dans le plasma. Grâce à un travail de modélisation analytique et numérique de ces principaux mécanismes, nous avons examiné de manière complète la génération d'impulsions THz pour des intensités allant de celles rencontrées en filamentation laser (10¹²-10¹⁴ W cm⁻²) jusqu'aux intensités relativistes (10¹⁵-10¹⁸ W cm⁻²), une fourchette d'intensités peu étudiée jusqu'à présent dans ce domaine. Il est déjà connu qu'à basses intensités la photoionization induite par le champ laser domine l'émission térahertz, laquelle dépend fortement de la configuration des couleurs (ou harmoniques) laser. Nous démontrons ici que, au-delà de la configuration laser ''classique'' à deux couleurs, coupler plusieurs fréquences laser suivant les harmoniques d'une forme d'onde en dents de scie est optimal pour renforcer la production de rayonnement. Les simulations prévoient une efficacité de conversion d'énergie THz de 2% avec quatre couleurs, valeur record inégalée à ce jour. De plus, en nous aidant d'une expérience faite dans l'air, nous identifions la signature de l'effet Kerr dans le spectre THz émis, qui, plus faible, se révèle complémentaire de la signature plasma. Quand l'intensité de l'impulsion laser est augmentée au-delà de 10¹⁵ W cm⁻², nous démontrons que le rayonnement térahertz émis croît de manière non-monotone, dû au fait qu'il existe une valeur d'intensité maximisant l'énergie THz produite par chaque couche électronique. Finalement, nous avons étudié en géométrie 2D l'effet combiné de la photoionization et des forces pondéromotrices plasma à des intensités proches de 10¹⁸ W cm⁻², nous permettant d'obtenir des champs THz excédant le GV/m dans l'argon. Ces dernières forces augmentent avec l'intensité laser et ouvrent des perspectives intéressantes pour la génération de champs térahertz très intenses dans le régime relativiste de l'interaction laser-matièreThe electromagnetic spectrum has a narrow frequency band, lying between microwaves and infrared, known as terahertz (THz) waves and extending from 0.1 to 30 THz. These waves, inaccessible until a recent past because they are situated at the boundary between electronics and optics, are raising interest because of their promising applications in several areas such as medical imaging and remote identification of explosives. However, producing intense THz radiation with amplitude belonging to the GV/m range should allow us to probe efficiently remote materials, which still remains an open issue. The goal of this thesis is precisely to study the generation of such intense THz radiation by coupling two ultrashort laser pulses -the fundamental and its second harmonic- able to ionize a gas target (for example, air or argon). The plasma created by photoionization then acts as a nonlinear frequency converter, transforming part of the laser energy into the THz band via a wide range of physical mechanisms including the Kerr effect, the photoionization and ponderomotive forces induced inside the plasma. By means of an analytical and numerical modeling of these key mechanisms, we have comprehensively examined the generation of THz pulses at laser intensities ranging from characteristic intensities met in laser filamentation (10¹²-10¹⁴ W cm⁻²) to sub-relativistic intensities (10¹⁵-10¹⁸ W cm⁻²), this latter intensity range having been little investigated so far in this domain. It is already known that at low intensities laser-induced photionization dominates in terahertzgeneration, which strongly depends on the configuration of the laser colours (or harmonics). We demonstrate here that, beyond the classical two-colour laser setup, coupling several laser frequencies following the harmonics of a sawtooth waveform is optimal to enhance THz production. Simulations predict a laser-to-THz energy conversion efficiency of 2% with four colours, a record value unequalled so far. Moreover, with an experiment realized in air, we identify the Kerr signature in the emitted THz spectrum, which, even weaker, looks complentary to the plasma signature. When the intensity of the laser pulse is increased beyond 10¹⁵ W cm⁻², we prove that the growth of the emitted terahertz radiation is nonmonotonic, due to the fact that that there exists an optimal intensity value that maximizes the THz energy produced by each electronic shell of the irradiated atom. Finally, we have studied in 2D geometry the combined effect of photoionization and ponderomotive forces at intensities close to 10¹⁸ W cm⁻², allowing us to obtain THz fields exceeding the GV/m threshold in argon. These latter forces increase with the laser intensity and thus open interesting perspectives for the generation of very intense terahertz fields in the relativistic regime of laser-matter interaction
El espectro electromagnético posee una zona estrecha, localizada entre las microondas y la radiación infrarroja, llamada región de las ondas Terahertz (THz), que está comprendida entre 0.1 et 30 THz. Estas ondas, durante mucho tiempo inaccesibles debido a que se encuentran situadas en la frontera entre la electrónica y la óptica, están despertando un interés creciente por la gran cantidad de aplicaciones prometedoras que poseen en diversos sectores científicos, como la imagen médica y la identificación de explosivos a distancia. No obstante, la producción de radiación THz intensa, de amplitud cercana al GV/m, la cual debería permitir sondar materiales energéticos a distancia, sigue siendo una cuestión abierta. Esta tesis tiene precisamente como objetivo el estudio de la generación de dicha radiación THz intensa acoplando dos pulsos láser —una onda fundamental y su segundo armónico— capaces de ionizar un gas (por ejemplo, aire o argón). El plasma creado de este modo desempeña el papel de convertidor no lineal de frecuencia, transformando una parte de la energía del láser en la banda THz mediante una rica gama de mecanismos físicos, entre los que destacan el efecto Kerr, la fotoionización y las fuerzas ponderomotrices inducidas dentro del plasma. Gracias a un trabajo de modelización tanto numérico como analítico de estos mecanismos clave, hemos examinado de forma integral la generación de pulsos THz a intensidades láser yendo desde las encontradas en la filamentación láser (10¹²-10¹⁴ W cm⁻²) hasta las cercanas al límite relativista (10¹⁵-10¹⁸ W cm⁻²), habiendo sido este último rango de intensidades poco estudiado en este campo hasta el presente. Ya es sabido que a bajas intensidades la fotoionización inducida por el láser domina la emisión Terahertz, la cual depende enormemente de la configuración de los colores (o armónicos) del láser. Demostramos aquí que, más allá de la “clásica” configuración del láser en dos colores, acoplar varias fréquencias láser siguiendo los armónicos de una forma de onda en diente de sierra es óptimo para incrementar la producción THz. Las simulaciones predicen una eficacia de conversión de energía THz de 2% empleando cuatro colores, un valor récord inigualado hasta hoy. Además, ayudándonos de un experimento realizado en aire, identificamos la firma del effecto Kerr en el espectro THz emitido, la cual, pese a ser más débil, resulta complementaria a la firma del plasma. Cuando se aumenta la intensidad del láser más allá de 10¹⁵ W cm⁻², demostramos que la radiación Terahertz emitida crece de manera no monotóna, debido a que existe un valor de intensidad que maximiza la energía THz producida por cada capa electrónica. Finalmente, hemos estudiado en geometría 2D el efecto conjunto de la fotoionización y de las fuerzas ponderomotrices a intensidades próximas a 10¹⁸ W cm⁻², lo que nos permite obtenter campos THz cuyas amplitudes exceden el GV/m en argon. Estas últimas fuerzas aumentan con la intensidad láser y, por tanto, ofrecen perspectivas interesantes para la generación de campos Terahertz muy intensos en un régimen de interacción láser-materia relativista
4
Suzanovičienė, Rasa. "Investigation of carrier kinetics in semiconductors by terahertz radiation pulses". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2010. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2010~D_20101116_163924-89818.
Resumen
Creation of ultrafast semiconductor components is inconceivable without understanding various processes of picoscond duration in semiconductors. These processes, as electron energy relaxation time or nonequiriblium carrier capture are very important for semiconductor photonics and terahertz range devices. Since now, the most popular tool of measuring ultrafast processes in semiconductors was picosecond or femtosecond laser pulses. In spite of excellent time resolution, optical pump – probe methods have a significant imperfection. Interpretation of the results can be very complicate. Also, the measured result can be affected by few variable parameters or interaction of various physical phenomenon. Therefore determinate results can be hardly related with electron time dependent characteristic. The aim of this dissertation was to measure electron energy relaxation times and electron life times by using terahertz pulses in narrow – gap semiconductors used for photoconductive terahertz emitters or detectors. In this dissertation, electron characteristic times witch describe various processes in semiconductor, were studied. These measurements were performed by optical pump – terahertz probe technique and time domain terahertz spectroscopy. The emission of terahertz pulses from the semiconductor surface, illuminated by femtosecond laser pulses, was investigated.Ultrasparčių puslaidininkinių komponentų kūrimas reikalauja gilesnio supratimo apie tai, kaip puslaidininkiuose vyksta fizikiniai procesai, trunkantys kelias pikosekundes ar net mažiau nei vieną pikosekundę. Tokie reiškiniai, kaip elektronų impulso ir energijos relaksacija bei nepusiausvyrųjų krūvininkų pagavimas yra labai svarbūs puslaidininkinių fotonikos ir terahercinio diapazono prietaisų veikimui. Iki pastarojo meto pagrindinis ultrasparčiųjų procesų puslaidininkiuose tyrimo įrankis buvo optiniai metodai, kuriuose elektronų dinamikai stebėti buvo pasitelkiami pikosekundinių ar femtosekundinių lazerių impulsai. Nepaisant išskirtinai didelės šių metodų laikinės skyros, optinio kaupinimo-zondavimo matavimų rezultatus yra palyginti sudėtinga interpretuoti. Šie rezultatai dažniausiai yra įtakojami kelių sistemos parametrų kitimo ir įvairių fizikinių reiškinių tarpusavio sąveikos, todėl sunkiai susiejamas su kuria nors elektronų laikine charakteristika. Disertacijos darbo tikslas – naudojant terahercinės spinduliuotės impulsus išmatuoti elektronų impulso ir energijos relaksacijos trukmes keliuose siauratarpiuose puslaidininkiuose bei jų gyvavimo trukmes medžiagose, skirtose fotolaidžių terahercinės spinduliuotės emiterių ir detektorių gamybai. Šioje disertacijoje yra pateikiami įvairių charakteringų elektroninius procesus puslaidininkiuose apibūdinančių trukmių matavimų naudojant terahercinės spinduliuotės impulsus rezultatai. Tokie tyrimai atlikti ir optinio žadinimo –... [toliau žr. visą tekstą]
5
Chen, Zhao S. M. Massachusetts Institute of Technology Department of Chemistry. "Generation of high power single-cycle and multiple-cycle terahertz pulses". Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/79269.
Resumen
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 131-141).
In this thesis, we present experimental methods and results of tabletop generation of high power single-cycle and frequency-tunable multiple-cycle terahertz (THz) pulses pumped with near-infrared ultrashort optical pulses at 1 kHz and 10 Hz repetition rates. Single-cycle THz pulses with sub-picosecond duration and more than 50 pJ pulse energy, and multiple-cycle THz pulses with picosecond duration and more than 10 pJ pulse energy, are achieved respectively. These THz outputs are very close approximations to Gaussian beams, and can be well collimated and focused into samples for time-resolved spectroscopic experiments. This may allow for explorations in coherent nonlinear spectroscopy in the THz region such as the photon echo and multidimensional spectroscopy, revealing novel phenomena in solids, liquids, gases, and complex materials.
by Zhao Chen.
S.M.
6
JAHANGIRI, Fazel. "Terahertz Emission from Gas and Atomic Cluster Plasmas Induced by Intense Femtosecond Laser Pulses". 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/157770.
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Mori, Kazuaki. "Terahertz-wave generation from atomic clusters under the irradiation of intense femtosecond laser pulses". Kyoto University, 2019. http://hdl.handle.net/2433/242607.
8
Bičiūnas, Andrius. "Semiconductor materials for components of optoelectronic terahertz systems activated by femtosecond 1 µm wavelength laser pulses". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20121107_091148-13422.
Resumen
The aim of dissertation was to develop and explore the semiconductor material terahertz (THz) pulse emitters, for Terahertz time–domain spectroscopy (THz–TDS) systems using a 1 μm wavelength femtosecond laser radiation. THz pulse generation and detection using optoelectronic semiconductor components in THz–TDS excited by femtosecond laser pulses become these days a powerful experimental technique. Traditionally, mode-locked Ti:sapphire lasers emitting at the wavelengths ~800 nm are used. However Ti:sapphire lasers require many-stage optical pumping arrangement, the system is quite bulky and complicated. The solution could be the lasers emitting in 1 – 1.55 µm, which can be directly pumped by diode laser bars. Recently, several compact, efficient and cost-effective solid-state and fiber laser systems that generate femtosecond pulses at near-infrared wavelengths have been developed and employed for activating THz–TDS systems. The main obstacle of these systems is the lack of material with appropriate bandgap, high dark resistivity and short (~ ps) carrier lifetimes.Disertacijos darbo tikslas buvo sukurti ir ištirti puslaidininkinius terahercinių (THz) impulsų emiterius ir detektorius, skirtus sistemoms, naudojančioms 1 μm bangos ilgio femtosekundinę lazerinę spinduliuotę. THz impulsų generavimo ir detektavimo sistema, kurios optoelektroninius puslaidininkinius komponentus aktyvuoja femtosekundiniai lazerio impulsai, yra plačiai taikoma terahercinėje laikinės srities spektroskopijoje. Tradiciškai tokiose sistemose naudojami Ti:safyre femtosekundiniai lazeriai, kurių spinduliuotės bangos ilgis yra ~800 nm. Šios sistemos nėra patogios dėl jų matmenų, nes lazeriai turi sudėtingą kelių pakopų kaupinimo sistemą. Pastaruoju metu THz impulsų generavimui vis dažniau naudojami femtosekundiniai kietakūniai ir šviesolaidiniai lazeriai, kurių spinduliuotės bangos ilgis patenka į artimosios IR spinduliuotės sritį. Tačiau šios sistemos vis dar neturi tinkamos medžiagos fotolaidiems elementams gaminti, kurie būtų žadinami 1 – 1,55 µm bangos ilgio lazeriais. Tokios medžiagos, visų pirmą, turi būti jautrios optinei spinduliuotei, o jų draustinės energijos tarpas turi atitikti žadinamos spinduliuotės fotonų energiją, be to sluoksniai turi pasižymėti didele tamsine varža bei labai trumpomis krūvininkų gyvavimo trukmėmis (~ 1 ps). Šioje disertacijoje yra pateikiami THz impulsų generavimo panaudojus puslaidininkių paviršius ir fotolaidžias antenas rezultatai, žadinant 1 µm bangos ilgio femtosekundiniais lazerio impulsais.
9
Harper, Matthew R. "Control and measurement of ultrafast pulses for pump/probe-based metrology". Thesis, St Andrews, 2007. http://hdl.handle.net/10023/430.
10
Jolly, Spencer Windhorst [Verfasser] y Andreas [Akademischer Betreuer] Maier. "Spectral Phase Manipulation of Optical Pump Pulses for mJ-Level Narrowband Terahertz Generation in PPLN / Spencer Windhorst Jolly ; Betreuer: Andreas Maier". Hamburg : Staats- und Universitätsbibliothek Hamburg, 2018. http://d-nb.info/1151322350/34.
11
Weerasekara, Aruna Bandara. "Electrical and Optical Characterization of Group III-V Heterostructures with Emphasis on Terahertz Devices". Digital Archive @ GSU, 2007. http://digitalarchive.gsu.edu/phy_astr_diss/16.
Resumen
Electrical and optical characterizations of heterostructures and thin films based on group III-V compound semiconductors are presented. Optical properties of GaMnN thin films grown by Metalorganic Chemical Vapor Deposition (MOCVD) on GaN/Sapphire templates were investigated using IR reflection spectroscopy. Experimental reflection spectra were fitted using a non - linear fitting algorithm, and the high frequency dielectric constant (ε∞), optical phonon frequencies of E1(TO) and E1(LO), and their oscillator strengths (S) and broadening constants (Γ) were obtained for GaMnN thin films with different Mn fraction. The high frequency dielectric constant (ε∞) of InN thin films grown by the high pressure chemical vapor deposition (HPCVD) method was also investigated by IR reflection spectroscopy and the average was found to vary between 7.0 - 8.6. The mobility of free carriers in InN thin films was calculated using the damping constant of the plasma oscillator. The terahertz detection capability of n-type GaAs/AlGaAs Heterojunction Interfacial Workfunction Internal Photoemission (HEIWIP) structures was demonstrated. A threshold frequency of 3.2 THz (93 µm) with a peak responsivity of 6.5 A/W at 7.1 THz was obtained using a 0.7 µm thick 1E18 cm−3 n - type doped GaAs emitter layer and a 1 µm thick undoped Al(0.04)Ga(0.96)As barrier layer. Using n - type doped GaAs emitter layers, the possibility of obtaining small workfunctions (∆) required for terahertz detectors has been successfully demonstrated. In addition, the possibility of using GaN (GaMnN) and InN materials for terahertz detection was investigated and a possible GaN base terahertz detector design is presented. The non - linear behavior of the Inter Pulse Time Intervals (IPTI) of neuron - like electric pulses triggered externally in a GaAs/InGaAs Multi Quantum Well (MQW) structure at low temperature (~10 K) was investigated. It was found that a grouping behavior of IPTIs exists at slow triggering pulse rates. Furthermore, the calculated correlation dimension reveals that the dimensionality of the system is higher than the average dimension found in most of the natural systems. Finally, an investigation of terahertz radiation efect on biological system is reported.
12
Hanoun, Christelle. "Development of time-stretch terahertz waveform recorders for high repetition rate accelerator-based light sources". Electronic Thesis or Diss., Université de Lille (2022-....), 2023. https://pepite-depot.univ-lille.fr/ToutIDP/EDSMRE/2023/2023ULILR072.pdf.
Resumen
Le travail de Thèse concerne le développement de systèmes permettant l'enregistrement de signaux électriques, en single-shot, avec des bandes passantes allant jusqu'à plusieurs térahertz (THz). Ce travail est motivé par des besoins importants dans le développement et la recherche sur les sources de lumière basées sur des accélérateurs (les centres de rayonnement synchrotron et les lasers à électrons libres). Ce travail est également motivé par les besoins récents de spectroscopie THz avec des fréquences d'acquisition élevées. Cette thèse se focalise sur le développement de systèmes de mesure où les ondes THz à analyser sont sondées au moyen d'un laser femtoseconde. Plus spécifiquement, le travail porte sur le développement de la technique dite du photonic time-stretch, et vise à résoudre plusieurs problèmes ouverts. Jusque récemment, les techniques de time-stretch souffraient d'une limite fondamentale sur leurs durées d'enregistrement et/ou leurs résolutions temporelles à des valeurs incompatibles avec de nombreuses applications dans le domaine des accélérateurs. Dans une première partie, le travail a consisté à tenter de résoudre ce problème en développant, au laboratoire PhLAM, un système d'enregistrement THz monocoup associant la technique du photonic time-stretch et la technique dite du Diversity Electro-Optic Sampling (DEOS). Le système d'enregistrement, basé sur un laser de sonde à 1030 nm a ensuite été testé lors de deux séries d'expériences sur les sources THz intense basées sur l'accélérateur de ELBE, à Dresde. La première expérience s'est focalisée sur la source CDR (Coherent Diffraction Radiation) de ELBE - une source THz émettant des impulsions “single cycle”. Le succès de cette expérience nous a ensuite mené à réaliser des mesures du rayonnement émis par le laser à électrons libres (FEL) Térahertz de FELBE. Ceci nous a permis de démontrer la possibilité d'enregistrer de signaux THz à une fréquence - record - de 13 MHz. De plus, d'un point de vue plus fondamental, l'étude expérimentale du démarrage du laser à électrons libres a permis - pour la première fois - de visualiser de façon directe le démarrage d'un laser impulsionnel, en enregistrant complètement les impulsions émises (c'est-à-dire leur amplitude et leur porteuse). Finalement, cette thèse s'est focalisée sur un problème ouvert différent, concernant le coût - extrêmement élevé - des systèmes de mesures THz de type time-stretch. En effet, ces systèmes de mesures requièrent des oscilloscopes avec des bandes passantes élevées (généralement au-delà de 10 ou 20 GHz). À partir d'une étude comparative détaillée, et de mesures effectuées à SOLEIL, nous avons démontré la supériorité d'une stratégie basée sur des lasers de sonde à 1550 nm, au lieu des lasers (essentiellement à 1030 nm) usuellement employés dans la littérature. En permettant l'utilisation d'oscilloscopes avec des bandes passantes relativement faibles (de l'ordre du GHz), ceci nous a permis de réduire les coûts de façon importante, permettant d'envisager une popularisation beaucoup plus importante de ces méthodes de time-stretch dans le domaine des accélérateurs et en spectroscopieTerahertz (THz) science lacks of non-destructive waveform recorders for single-shot measurements of ultrafast signals. Such recording systems are particularly needed in accelerator-based light sources, such as synchrotron radiation facilities and Free-Electron Lasers (FEL). Single-shot operation is required for monitoring the emission of THz FELs, as well as the emission by other novel coherent THz sources. Moreover, single-shot recording systems are also required for monitoring shot-to-shot fluctuations of relativistic electron bunch properties, either for fundamental research, and in routine accelerator operation. This Thesis focuses on the development of THz recorders, using laser probes, that can operate at high repetition rates, typically in the Megahertz range. A main point of the strategy consists of using the so-called photonic time-stretch technique, for imprinting the THz waveform under interest onto a chirped laser pulse, and then to stretch it in time, so that it can be recorded by an oscilloscope. Two main designs are presented. In a first time we present a time-stretch-based recorder that is able to record waveforms with unprecedented duration and/or time resolution, by associating the time-stretch technique, with the recently developed Diversity Electro-Optic Sampling method (DEOS). We then present the first tests of this method on the THz Coherent Diffraction Radiation beamline of the ELBE facility (at the Helmoltz Zentrum Dresden Rossendorf). Using this system, we then present the first measurements of the pulses emitted by a THz Free-Electron Laser, the FELBE FEL, operating at 13 MHz repetition rate. This represents the first complete recording of pulses (amplitude and carrier) not only in a Free-Electron Laser, but also in a mode locked laser in general. Finally, we address the open problem of costs in THz time stretch systems, which are dominated by the required high bandwidth oscilloscopes (several hundreds of k€ as of 2023). We show that, when using the 1550 nm wavelength for the laser probe, special designs of THz time-strech digitizers can lead to much lower costs. We finally show a proof-of concept test of this method at the THz AILES beamline of the SOLEIL facility
13
Li, Dazhang. "On-chip pulsed terahertz systems". Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531524.
14
Padgett, Nicholas C. "High Powered Pulsed Terahertz Light Generation from Superconducting Antenna Arrays". Wright State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=wright148457888216279.
15
Pickwell, Emma. "Biological applications of terahertz pulsed imaging and spectroscopy". Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.444102.
16
Woodward, Ruth Mary. "Terahertz pulsed imaging and spectroscopy applied to dermatology". Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619981.
17
Handley, James William. "Time frequency analysis techniques in terahertz pulsed imaging". Thesis, University of Leeds, 2003. http://etheses.whiterose.ac.uk/1317/.
Resumen
Terahertz (THz) radiation is abundant in the natural world yet very hard to harness in the laboratory. Forming the boundary between `radio' and `light', the so called "terahertz gap" results from the failure of optical techniques to operate below a few hundred terahertz, and likewise the failure of electronic methods to operate above a few hundred gigahertz. However, recent advances in opto-electronic and semiconductor technology have enabled bright THz radiation to be coherently generated and detected, and THz imaging systems are now commercially available, if still very expensive. Terahertz pulsed imaging data are unusual in that an entire time series is `behind' every pixel of the image. While resulting in rich data sets, this high dimensionality necessitates some form of distillation or extraction of pertinent features before images can be formed. Within this thesis the technology of THz pulsed imaging is examined, together with the imaging modalities that are employed and the type of data that are acquired. The sources of noise are categorised, and it is demonstrated that this noise can be modelled by the family of stable distributions, but that it is neither normally distributed nor distributed according to a simple mixture of Gaussians. Joint time-frequency techniques such as those used in RADAR or ultrasound - windowed Fourier transforms and wavelet transforms - are applied to THz data, and are shown to be appropriate tools to use when analysing and processing THz pulses, particularly in signal compression. Finally, clustering algorithms in time, frequency, and time-frequency based feature spaces demonstrate that such tools have potential application in the segmentation of THz images into their constituent regions. The analyses herein improve our understanding of the nature of THz data, and the techniques developed are steps along the road to move THz imaging into real world applications, such as dental and medical imaging and diagnosis.
18
Wang, Feihu. "Ultrafast terahertz pulse generation from quantum cascade lasers". Electronic Thesis or Diss., Paris 6, 2016. http://www.theses.fr/2016PA066752.
Resumen
Lasers à cascades quantiques (LCQs) THz sont des dispositifs à semi-conducteurs fondamentaux pour l'action du laser dans la gamme THz. Des évolutions considérables ont été réalisées dans la dernière décennie en termes de fonctionnement de la température et de la puissance de sortie. LCQs THz peuvent posséder de bandes spectrales très larges, les rendant approprié pour la génération d'impulsions THz ultracourtes par blocage de mode. Cependant, à ce jour, la génération d'impulsions THz de LCQ a été limitée à 10 - 20 ps, en dépit de plusieurs années d'efforts de recherche. Dans cette thèse, ce goulot d'étranglement dans la technologie QCL est étudié et surmontée. Plusieurs étapes qui ont permis la réalisation de génération d'impulsions ultracourtes de LCQ ont été réalisées. Performances de "state-of-the-art" actuelles sont représentés, à l'aide de LCQ avec une bande passante étroite dans des guides d'ondes "single-plasmon" et des impulsions THz de 20 ps sont générés à basse température (10K). Ceci est suivi par, pour la première fois, le verrouillage de modes des LCQs des bandes spectrales larges dans les guides d'onde métal-métal à des températures élevées (77k). Même avec de bandes spectrales larges, les impulsions obtenus étaient seulement 11 ps et nous montrent que la dispersion de l'indice et la modulation électrique sont les facteurs critiques. Enfin, ces effets sont compensés par un interféromètre de Gires-Tournois et un modulation de perte. Cette approche permet de générer des impulsions aussi courtes que 4 ps, avec la possibilité d'aller beaucoup plus loin dans la sous-picosecondeTHz quantum cascade lasers (QCLs) are foundational semiconductor devices for laser action in the THz range. Considerable developments have been made in the last decade in terms of temperature operation and high output power. THz QCLs can also possess extremely large spectral bandwidths, rendering them suitable for ultrashort THz pulse generation through modelocking, with pulse widths of a few picoseconds theoretically obtainable. However, to date, the generation of THz pulses from QCLs has been limited to 10 - 20 ps, despite several years of research effort. In this thesis, this bottleneck in QCL technology is investigated and overcome. Several milestones have been achieved that permitted the realization of ultrashort pulse generation from QCLs. Current state-of-the-art performances are shown, using narrow spectral bandwidth QCLs in single-plasmon waveguides, and where modelocking results in 20 ps long THz pulses at low temperatures (10K). This is followed by, for the first time, mode-locking of broad spectral bandwidth QCLs in sub-wavelength metal-metal waveguides at ‘high’ temperatures (77K). Even with large spectral bandwidths, the shortest pulses achieved were only 11 ps and we show that the index dispersion and the electrical modulation are the critical factors. Finally, these effects are compensated through a Gires-Tournois interferometer and an extra loss mechanism, respectively, integrated monolithically onto a QCL. This approach permits to generate pulses as short as 4 ps, with the potential to go considerably further to the sub-picosecond or single cycle regime
19
Stone, Michael Raymond. "Photoconductive emitters for pulsed and continuous-wave terahertz generation". Thesis, University of Leeds, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417735.
20
Wall, Alexander. "Characterisation of tablets and roller-compacted ribbons with terahertz time-domain pulsed imaging". Thesis, De Montfort University, 2015. http://hdl.handle.net/2086/11152.
Resumen
The pharmaceutical process of dry granulation using roller-compaction (DG/RC) is effectively a non-batch based procedure orientated to deliver a continuous stream of material free of a pre-defined batch-size with reduced plant equipment/scale-up R&D resources and an enhanced work-throughput, particularly suitable for moisture sensitive formulation. The desirable accreditations of DG/RC are many; yet by the nature of a more flexible approach than (i.e. wet-granulation), it must be highly monitored and controlled to accomplish higher-throughput rates and reduced ‘static’ material testing stages. To monitor rapidly and in-line with production, pre-granulated ribbons of RC (which highly correlates to the post milled granulates), terahertz time-domain spectroscopy (TDS) is used to elucidate the key physical attributes of post-compression density and thickness uniformity, key to end-product consistency. Invariably a great number of conditions apply to DG/RC (viz: System design, material characteristics, environmental and unit configuration), although widely regarded as the key processing parameters (PP’s) are roll-pressure and roll-gap [1-4]. The target of the study is to derive a strategy to position TDS as PAT to DG/RC. Two terahertz time-domain TD methods of a conventional transmission setup and reflection (TPI) THz analysis are used on standards of glass slides for verifying the interpretational foundations of the TD methods. Achieving RI/thickness error-discrepancies +2.2 to -0.4% c.f. literature ([150]) values provides foundations to test the solid-fraction ratios of pharma tablets with regard to RI’s being surrogate values to SF/path-length (R2 = 1). Combining transmission principles to the portion of reflected EMR removes the pre-requisite for RI or path-length knowledge, giving +1.5 to +2.4% RI agreement (vs. frequency-domain attained results) thus enabling thickness estimations to be above 95% against physical micrometre judgement in all models. Augmentation of the TD methods, refined in Experimental chapter 2 ,then chiefly focuses on TPI as the principle THz-TD method (as the most ideal tool for PAT) for adopting the RI measures for ribbon uniformity analysis in Experimental chapter 4 in an off-line environment again resulting in RI and thicknesses < 5 % error of known parameters of thickness and further use of RI as a proxy porosity equivalent to gas pycnometry. Elucidated in the work are the limitations encountered with tablets and RC’s, data interpretation of industrial considerations. Experimental chapter 3 diverges from RI to differentiate thickness in-order to assess the FD transmission for non-destructive mechanical assessment. This demonstrates a clear relationship between compaction force and the surrogate value for density, following a linear trend below a certain threshold of force. The ‘threshold’ value is observed for less massive tablets, and concluded is that the mechanistic interplay and permanent (plastic) consolidation is greater in instances where compaction-force increases proportionally with target-fill weights, and thus the various behaviour of MCC to stress.
21
Huang, Wenqian Ronny. "High field, high efficiency terahertz pulse generation by optical rectification". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87946.
Resumen
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 51-55).
The great difficulty of producing high intensity radiation in the terahertz (THz) spectral region by conventional electronics has stimulated interest in development of sources based on photonics. Optical rectification in lithium niobate is an attractive approach, because it supports high generation efficiencies, uses low cost, bulk LN crystals, and is powered by common Yb-doped lasers at wavelengths of around 1 Pm. In this work, a theoretical framework for THz generation by optical rectification is developed. Several novel methods for optimizing the generation efficiency are shown, including pump beam imaging, pump pulse optimization, cryogenic cooling, and THz antirefiection coating. Finally, experimental results will be presented showing a THz generation efficiency of 3.7%, which is 10x higher than current state-of-the-art. The generated few-cycle THz pulses can be used for coherent control of electrons, setting the stage for compact, table-top accelerators.
by Wenqian Ronny Huang.
S.M.
22
Zeitler, J. Axel y n/a. "Physical characterisation of pharmaceutical solids by terahertz pulsed spectroscopy and imaging". University of Otago. School of Pharmacy, 2007. http://adt.otago.ac.nz./public/adt-NZDU20070515.131938.
Resumen
Terahertz radiation refers to a specific part of the electromagnetic spectrum, flanked by microwave and infrared radiation at the higher and lower frequency end respectively. This thesis is about the development of applications using a new source of pulsed, coherent light for the physical characterisation of solids in the pharmaceutical setting.
Terahertz radiation has excellent potential in the advancement of science but is, as yet, largely unexplored. Recent developments in semiconductor physics have made it possible to provide light at terahertz frequencies (a frequency of 1 THz equals a wavelength of 0.3 mm) in a relatively easy way. Light located in this range of the electromagnetic spectrum was very difficult to generate previously. It has unique properties in that it is possible to extract the full spectroscopic fingerprint of the materials by looking at the frequency response of the terahertz pulse. Here, vibrations of the whole molecule are probed rather than just the vibrations of single functional moieties within a molecules as is the case in infrared spectroscopy, which makes terahertz spectroscopy a very powerful tool for the analysis of the complex solid-state materials properties.
In addition to structural information it easily penetrates through most plastics and polymeric materials used as excipients for pharmaceutical tablets. It is therefore especially useful for non-destructive imaging applications.
At the example of polymorphic phase transitions, dehydration processes and crystallization experiments from the amorphous phase the potential of terahertz spectroscopy for pharmaceutical analysis was systematically investigated. In addition, a novel concept for using terahertz radiation in structural imaging of pharmaceutical dosage forms was developed.
The technology, thus far predominantly used for the analysis of inorganic materials and semiconductors in particular, is now mature enough for its application to a wider field and to help with the understanding of fundamental and exciting new challenges at the interface between physics and the life sciences.
Together with a comparison of this new technology to the established techniques in physical characterisation an initial attempt to understand and interpret the spectral information provided is presented. The potential for future applications is discussed.
23
Reese, George Edward. "Terahertz Pulsed Imaging of lower gastrointestinal mucosa : an in vitro study". Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/26989.
Resumen
Medical imaging using Terahertz frequency radiation is in its infancy. Optical adjuncts to enhance the diagnostic precision of white light endoscopy are not new and almost all wavelengths of the electromagnetic spectrum have, at some point, been investigated to this end. The ultimate aim of an endoscopic technique is to identify 100% of mucosal lesions and to classify them with 100% specificity. Methods: This thesis examined the sensitivity and specificity of current technology to accurately identify colonic pathology using a diagnostic precision analysis of published data. The effect of biomaterials such as blood, mucus and faeces on Terahertz radiation was assessed using human tissue samples from health volunteers. The ability to discriminate pathological from normal colonic mucosa was assessed using terahertz radiation to interrogate excised samples of human colon. The physical nature of variation between pathological and normal colonic mucosa was assessed using histological markers in an attempt to identify the cause of terahertz radiation contrast. Results: Current technology has a sensitivity of 95% and a specificity of 78% in a non- inflamed colon. Terahertz pulsed imaging is a sensitive and specific technique for in vitro classification of colonic mucosal pathology. TPI may be a useful adjunct in the presence of inflamed mucosal tissue. Although there were too few data from the present study to quantify any potential benefit. The effects of blood, stool and mucus on TPI are similar but less pronounced than water. Immunohistochemical analysis has demonstrated an association between vascular and lymphatic density with neoplasia. This may be a mechanism for TPI discrimination of colonic pathology. TPI could in the future contribute to a minimally invasive method of in vivo diagnosis of colonic dysplasia or malignancy. Larger scale and in vivo trials of the technology are necessary to further investigate the potential clinical benefit.
24
Smith, William. "Development of techniques for magneto-spectroscopy at terahertz frequencies". Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/development-of-techniques-for-magnetospectroscopy-at-terahertz-frequencies(b9445541-8050-4f9b-9b1f-6a2d0c2935c3).html.
Resumen
In this thesis, I present my research into the development and use of a magneto-spectrometer operating at terahertz frequencies. Molecular samples with unpaired electrons were studied using electron paramagnetic resonance (EPR) spectroscopy and the properties of semiconducting samples were measured by cyclotron resonance. A terahertz time-domain spectrometer was constructed, fine-tuned and benchmarked. The use of a large area photoconductive antenna (PCA), with a bias voltage modulated at 1 MHz, allowed for a signal-to-noise ratio of 13800:1 to be achieved, which was equal or superior to comparable systems in use. The thermal behaviour of the PCA was studied and modelled to find that a 28% increase in emission occurred when the PCA was cooled to 100 K and a 22% increase in the maximum usable bias voltage was possible when the emitter substrate was cooled in a liquid nitrogen cryostat. The spectrometer was used to study a mixed type I/type II GaAs quantum well heterostructure as a test sample, in the process extending the existing research performed on this controllable terahertz filter. Together with a Gunn diode, bolometer and a Schottky diode, a pulsed magnet was developed into a 135 GHz, continuous-wave EPR spectrometer. EPR was detected in DPPH allowing for the spectrometer magnetic field accuracy to be determined and in ruby, which provided the crystal orientation of the sample and the base temperature of the spectrometer. Following this, three novel mixed-metal fluoride-centred triangles were studied on a multiple frequency EPR spectrometer allowing for the exchange interactions to be calculated along with the g-factors for two energy states. Two dimetallic cobalt complexes were studied to find that small changes to the molecules resulted in significant changes in the measured EPR spectra and so these molecules could be a useful part of the study of exchange coupled systems. The terahertz time-domain spectrometer was then combined with the pulsed magnet and an asynchronous optical sampling (ASOPS) system. Use of ASOPS allowed the number of waveforms measurable during a magnetic field pulse to be increased by at least a factor of 20 compared to contemporary alternatives. The spectrometer was used study cyclotron resonance in a two-dimensional electron gas (2DEG) formed at a GaAs/AlGaAs interface. Cyclotron resonance was successfully measured in the 2DEG at frequencies up to 1.6 THz, finding an electron effective mass of 0.071 m e , a sheet electron density of 3.3 × 10 11 cm -2 and a mobility of 1.5 × 10 5 cm 2 V -1 s -1 . Furthermore, using this system, the detection of EPR in a ruby sample was achieved, providing the first demonstration of ASOPS being used to study EPR at terahertz frequencies.
25
Ehberger, Dominik [Verfasser] y Ferenc [Akademischer Betreuer] Krausz. "Electron pulse control with terahertz fields / Dominik Ehberger ; Betreuer: Ferenc Krausz". München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/1196968543/34.
26
Fang, Qiang. "2 μm Pulsed Fiber Laser Sources and Their Application in Terahertz Generation". Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/232475.
Resumen
In this dissertation, an all-fiber-based single frequency nanosecond pulsed laser system at ~ 1918.4 nm in master-oscillator-power-amplifier (MOPA) configuration is present. The nanosecond pulse seed is achieved by directly modulating a continuous wave (CW) single frequency fiber laser using a fast electro-optical modulator (EOM) driven by an arbitrary waveform generator (AWG). One piece of single mode, large core, polarization-maintaining (PM) highly thulium-doped (Tm-doped) germanate glass fiber (LC-TGF) is used to boost the pulse power and pulse energy of these modulated pulses in the final power amplifier. This laser system can work in both high power and high energy regime: in high power regime, to the best of our knowledge, the highest average power 16 W and peak power 78.1 kW are achieved for single frequency transform-limited ~2.0 ns pulses at 500 kHz and 100 kHz repetition rate, respectively: In high energy regime, nearly 1 mJ and half mJ pulse energy is obtained for ~15 ns pulses at 1 kHz repetition rate and 5 kHz repetition rate, respectively. Theoretical modeling of the large-core highly Tm-doped germanate glass double-cladding fiber amplifier (LC-TG-DC-FA) is also present for 2&mum nanosecond pulse amplification. A good agreement between the theoretical and experimental results is achieved. The model can simulate the evolution of pump power, signal energy, pulse shape and the amplified stimulated emission (ASE) in the amplifier. It can also be utilized to investigate the dependence of the stored energy in the LC-TGF on the pump power, seed energy and repetition rate, which can be used to design and optimize the LC-TG-DC-FA to achieve higher pulse energy and average power. Two channel of high energy nanosecond pulses (at 1918.4 nm and 1938 nm) are utilized to generate THz wave in a quasi-phase-matched (QPM) gallium arsenide (GaAs) based on difference frequency generation. THz wave with ~ 5.4μW average power and ~18 mW peak power has been achieved. Besides, one model is built to simulate a singly resonated THz parametric oscillator. The threshold, the dependence of output THz energy on pump energy has been investigated through this model. One pump enhanced THz parametric oscillator has been proposed. The enhancement factor of the nanosecond pulses in a bow-tie ring cavity has been calculated for different pulse duration, cavity length and the transmission of the coupler. And the laser resonances in the ring cavity have been observed by using a piezo to periodically adjust the cavity length. We also build an all-fiber thulium-doped wavelength tunable mode-locked laser operating near 2&mum. Reliable self-starting mode locking over a large tuning range (>50 nm) using fiber taper based carbon nanotube (FTCNT) saturable absorber (SA) is observed. Spectral tuning is achieved by stretching another fiber taper. To the best of our knowledge, this is the first demonstration of an all-fiber wavelength tunable mode-locked laser near 2&mum.
27
Molis, Gediminas. "Investigation of the terahertz pulse generation from the narrow band gap semiconductor surfaces". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2010. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2010~D_20100623_093655-47390.
Resumen
Generation of terahertz radiation from semiconductor surfaces has great potential for investigation of physical properties of semiconductors. This work focuses on the semiconductor research when generating terahertz pulses from a variety of semiconductor surfaces. THz radiation from semiconductor surfaces can be generated on a whole range of physical mechanisms: the surface field screening, photo-Dember effect, the optical rectification, electric field induced optical rectification, plasma oscillations, coherent phonons and plasmons. A number of important semiconductor parameters such as refractive index, mobility, carrier relaxation time and higher conductivity valley positions can be measured using THz generation from semiconductor surface technique. In this work THz radiation generation mechanisms were investigated when changing excitation conditions: ambient temperature, magnetic field, laser wavelength and intensity, pulse duration. After tests with variety different semiconductors it was found that p-InAs is the best surface emitter when excitation laser wavelength is 800 nm. Using THz excitation spectroscopy the intervalley distances were measured directly, for the first time, in two InxGa1-xAs, InAs and InSb samples.THz spinduliuotės generavimas iš puslaidininkių paviršiaus turi didelį potencialą puslaidininkių fizikinėms savybėms tirti. Šis darbas skiriamas puslaidininkių tyrimams generuojant THz impulsus iš jų paviršių, apšviestų femtosekundiniais lazerio impulsais. THz spinduliuotė iš puslaidininkių paviršių gali būti generuojama dėl visos eilės fizikinių mechanizmų: paviršinio lauko ekranavimo, foto-Demberio efekto, optinio lyginimo, elektriniu lauku indukuoto optinio lyginimo, plazminių svyravimų, koherentinių fononų ir plazmonų. Tiriant THz spinduliuotės generacijos mechanizmus galima išmatuoti daug svarbių puslaidininkių parametrų, tokių kaip lūžio rodiklis, judris, krūvininkų gyvavimo trukmė, aukštesniųjų laidumo slėnių padėtys. Darbo metu tirti THz spinduliuotės generacijos puslaidininkio paviršiuje mechanizmai keičiant žadinimo sąlygas: aplinkos temperatūrą, magnetinį lauką, žadinančio lazerio bangos ilgį ir intensyvumą, bei impulso trukmę. Ištyrus visą eilę įvairių puslaidininkių nustatyta, kad geriausias THz spinduliuotės emiteris žadinant 800 nm bangos ilgio spinduliuote yra p-InAs. Pirmą kartą THz žadinimo spektroskopijos metodu tiesiogiai išmatuoti tarpslėniniai atstumai InxGa1-xAs , InAs ir InSb bandiniuose.
28
Velauthapillai, Ajanthkrishna [Verfasser] y Martin [Akademischer Betreuer] Koch. "Spektrale Verbreiterung von Terahertz-Pulsen mittels eines Schottkykontakt-Wellenleiters / Ajanthkrishna Velauthapillai ; Betreuer: Martin Koch". Marburg : Philipps-Universität Marburg, 2017. http://d-nb.info/1136078010/34.
29
Leigh, Matthew. "HIGH POWER PULSED FIBER LASER SOURCES AND THEIR USE IN TERAHERTZ GENERATION ". Diss., The University of Arizona, 2008. http://hdl.handle.net/10150/193797.
Resumen
In this dissertation I report the development of high power pulsed fiber laser systems. These systems utilize phosphate glass fiber for active elements, instead of the industry-standard silica fiber. Because the phosphate glass allows for much higher doping of rare-earth ions than silica fibers, much shorter phosphate fibers can be used to achieve the same gain as longer silica fibers.This single-frequency laser technology was used to develop an all-fiber actively Q-switched fiber lasers. A short cavity is used to create large spacing between longitudinal modes. Using this method, we demonstrated the first all-fiber Q-switched fiber laser in the 1 micron region.In addition to creating high peak powers with Q-switched lasers, created even higher powers using fiber amplifier systems. High power fiber lasers typically produce spectral broadening through the nonlinear effects of stimulated Raman scattering, stimulated Brullion scattering, and self-phase modulation. The thresholds for these nonlinearities scale inversely with intensity and length. Thus, we used a short phosphate fiber gain stage to reduce the length, and a large core fiber final stage to reduce intensity. In this way we were able to generate high peak power pulses while avoiding visible nonlinearities, and keeping a narrow bandwidth.The immediate goal of developing these high power fiber laser systems was to generate narrowband terahertz radiation. Two different wavelengths were combined into the final amplifier stage at orthogonal polarizations. These were collimated and directed into a GaSe crystal, which has a very high figure of merit for THz generation. The two wavelengths combined in the crystal through the process of nonlinear difference frequency generation. This produced a narrowband beam of THz pulses, at higher powers than previous narrowband THz pulses produced by eyesafe fiber lasers.
30
Rasekh, Payman. "Kerr Effect at the THz Frequencies". Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/41085.
Resumen
This doctoral dissertation focuses on the nonlinear optical response of water vapour as well as some solids at terahertz (THz) frequencies. In this study, the propagation of broadband single-cycle THz pulses through a medium with the third-order nonlinear optical response is theoretically investigated. Also, a technique to measure the nonlinear response of transparent materials based on the time-domain THz spectroscopy is developed, which provides frequency dispersion curves of the nonlinear Kerr coefficient (n₂).
A numerical model is used to simulate the THz pulse propagation. This model takes
into account non-paraxial effects, self-focusing, and diffraction, as well as dispersion,
in both the linear and nonlinear optical regimes. The contribution of non-instantaneous
Kerr-type nonlinearity to the overall instantaneous and delayed Kerr effect at the THz
frequencies is investigated. It is shown how increasing the nonlinear relaxation time and its dispersion modifies the THz pulse after the propagation through a transparent medium. The effect of linear dispersion on self-action during pulse propagation is also discussed.
Moreover, the nonlinear spectroscopy of water vapour at THz frequencies is reported. Atmospheric water vapour has a rich spectrum with several strong resonances at frequencies below 3 THz, falling within the range of operation of most existing THz sources. An extremely large nonlinear response to THz radiation is observed at the positions of these resonances. Using the optical Kerr model for the nonlinear response, a minimum nonlinear refractive index of the order of 10² m²/W is estimated. The results provide insight into the energy levels of the water molecule and give a more accurate picture of its response to electromagnetic radiation, paving the way to more accurate THz spectroscopy, imaging, and sensing systems, and thereby facilitating future emerging THz technologies.
Finally, the nonlinear response of solids at THz frequencies is studied. It has been
shown that a phonon-induced THz Kerr effect can result in a larger nonlinear refractive
index than the nonlinear refractive index at the visible or near-infrared range (optical
Kerr effect). This pronounced nonlinear optical behavior is verified using a time-domain characterization approach. The results indicate a large delay occurred to the THz fields as they transmit through some of the material samples. In the frequency domain, the induced nonlinear phase shift of the intense THz field is shown to be relatively large of the order of 0.1 rad. From the phase information, the nonlinear phase is extracted by which the dispersion profile of n₂ is obtained.
31
Loata, Gabriel C. "Investigation of low-temperature-grown GaAs photoconductive antennae for continuous-wave and pulsed terahertz generation /". [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=985715871.
32
Souza, Fabricio Macedo de. "Dinâmica de plasma e fônon e emissão de radiação terahertz em superfícies de GaAs e telúrio excitadas por pulsos ultracurtos". Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-18112013-111000/.
Resumen
Após a excitação de uma amostra semicondutora por um pulso ultracurto, os fotoporadores interagem com a rede excitando modos longitudinais ópticos. Essa interação provoca variações no índice de refração do material, produzindo modulações na resposta óptica do meio (efeito eletro-óptico). Por outro lado, esta dinâmica origina polarizações dependentes do tempo o que gera emissão de radiação terahertz. Experimentos recentes (pump-probe) observaram modulações do campo através de medidas da refletividade resolvidas no tempo. A refletividade e o campo estão relacionados segundo o efeito eletro-óptico. Também se resolve temporalmente o campo irradiado pela amostra, através de antenas que operam na faixa de terahertz. Tanto as medidas eletro-ópticas quanto de emissão terahertz fornecem informações sobre a interação dinâmica do plasma com a rede após a excitação óptica. Nesse trabalho simulamos a interação dinâmica de plasma e fônons em n-GaAs e Telúrio (\"bulk\") após estes serem excitados por um pulso ultracurto. Utilizamos equações hidrodinâmicas para descrever transporte de cargas e uma equação fenomenológica de oscilador harmônico forçado, para descrever oscilações longitudinais ópticas da rede. Complementando nossa descrição temos a equação de Poisson, com a qual calculamos o campo gerado pelo plasma e pela polarização da rede semicondutora. Essas equações constituem um sistema de seis equações diferencias (quatro parciais) acopladas. Para resolvê-las utilizamos o método das diferenças finitas. Do cálculo numérico obtemos a evolução temporal do campo elétrico no interior do material. Com esse campo determinamos as freqüências de oscilação do sistema e calculamos o campo irradiado. Nossos resultados apresentam acordo qualitativo com os experimentosAbove-band-gap optical excitation of semiconductors generates highly non-equilibrium photocarriers which interact with phonons thus exciting vibrational modes in the system. This interaction induces refractive-index changes via the electro-optic effect. Moreover it gives rise to electromagnetic radiation at characteristic frequencies (terahertz). Both effects have been measured by time-resolved ultra fast spectroscopy. Recent pump-probe experiments have found strong modulations of the internal electric field through electro-optic measurements. The emitted electromagnetic radiation has also been detected by a terahertz dipole antenna. Both electro-optic and terahertz emission measurements provide information about the coupled dynamics of photocarriers and phonons. In this work we simulate the dynamics of plasmon-phonon coupled modes in n-GaAs and Tellurium (bulk) following ultrafast laser excitation. The time evolution of the photocarrier densities and currents is described semi classically in terms of the moments of the Boltzmann equation. Phonon effects are accounted for by considering a phenomenological driven-harmonic-oscillator equation, which is coupled to the electron-hole plasma via Poisson\'s equation. These equations constitute a coupled set of differential equations. We use finite differencing to solve these equations. From the numerical results for the evolution of internal fields we can calculate both the characteristic frequencies of system and its terahertz radiation spectrum. Our results are consistent with recent experimental data
33
Brock, Daniela [Verfasser]. "Terahertz Pulsed Imaging for Quality by Design Driven Development of Active-Coated OROS Tablets / Daniela Brock". München : Verlag Dr. Hut, 2013. http://d-nb.info/104512673X/34.
34
Rämer, Jan-Martin [Verfasser]. "A Terahertz Time-Domain Spectroscopy-based Vector Network Analyzer Setup with Integrated Pulse Shaping / Jan-Martin Rämer". München : Verlag Dr. Hut, 2016. http://d-nb.info/1097818438/34.
35
Jewariya, Mukesh. "Resonant Excitation of Large Amplitude Anharmonic Vibrations of Amino acids Micro Crystals by an Intense Monocycle Terahertz Pulse". 京都大学 (Kyoto University), 2010. http://hdl.handle.net/2433/126826.
36
Globisch, Björn [Verfasser] y Martin [Akademischer Betreuer] Koch. "Photoconductive Terahertz Emitters and Detectors for the Operation with 1550 nm Pulsed Fiber Lasers / Björn Globisch ; Betreuer: Martin Koch". Marburg : Philipps-Universität Marburg, 2017. http://d-nb.info/1136077995/34.
37
Voß, Daniel [Verfasser], Hartmut [Gutachter] Roskos y John [Gutachter] Sheridan. "Investigations on terahertz imaging with pulsed optical parametric oscillator radiation and heterodyne Fourier techniques / Daniel Voß ; Gutachter: Hartmut Roskos, John Sheridan". Frankfurt am Main : Universitätsbibliothek Johann Christian Senckenberg, 2019. http://d-nb.info/1184986185/34.
38
Pistore, Valentino. "Modelocking of THz quantum cascade lasers : dispersion control and non-linearities". Electronic Thesis or Diss., Sorbonne université, 2019. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2019SORUS302.pdf.
Resumen
Les LCQ THz sont aujourd'hui considérés comme une plate-forme prometteuse pour la génération d’impulsions THz intenses et ultracourtes. En raison de leur temps de récupération du gain rapide, le verrouillage en mode passif des LCQ THz s'est jusqu'à présent révélé difficile. Au contraire, le verrouillage de mode actif avec une modulation hyperfréquence a été appliqué avec succès. La durée du pouls a cependant été difficile à réduire malgré des années de recherche. En 2017, notre groupe a généré des impulsions THz de 4ps grâce à l'application d'une structure intégrée (un GTI) visant à réduire la dispersion chromatique. La recherche dans cette thèse commence à partir de ce point. Je présente notamment l'ingénierie de dispersion dans les LCQ THz afin d'obtenir des impulsions très courtes, même à partir de dispositifs à bande relativement étroite. Ceci est réalisé en utilisant des méthodes de modulation actives éprouvées qui peuvent ajuster l’émission de LCQ d’un régime de dispersion élevé à faible. Je montre également que les LCQ THz peuvent présenter une forte modulation d'amplitude de leur profil d'émission et qu'ils peuvent émettre spontanément des impulsions à la suite d'un mécanisme d’auto-verrouillage. En conséquence, cela indique que le temps de récupération de gain rapide n'est pas un facteur limitant pour la génération d'impulsions. Je montre également ce schéma passif dans le cadre des premières démonstrations du verrouillage en mode harmonique de LCQ THz. Enfin, un nouveau phénomène est présenté où les modes d’une LCQ THz peuvent battre ensemble pour générer une émission de micro-ondes dans l’espace libreTHz QCLs are nowadays considered a promising platform for the generation of intense and ultrashort THz pulses. Owing to their fast gain recovery time, passive modelocking of THz QCLs has so far proved to be difficult. On the contrary, active modelocking with a microwave modulation has been successfully applied. The pulse duration, however, has been arduous to reduce despite years of research. In 2017, THz pulses as short as 4ps have been generated by our group with the application of an integrated structure (a GTI) aiming to reduce the chromatic dispersion. The research in this thesis starts from this point.In particular, I present dispersion engineering in THz QCLs in order to obtain very short pulses even from relatively narrow-band devices. This is achieved using proven active modulation methods that can tune the QCL emission from high to low dispersion regimes. I also show that THz QCLs can present a strong amplitude modulation of their emission profile and that they can spontaneously emit pulses as a result of a self-locking mechanism, contrary to the expected frequency modulated response. As a consequence, this indicates that the fast gain recovery time is not a limiting factor for the generation of pulses. I also show this passive self-locking scheme for passive pulse generation in the framework of the first demonstrations of harmonic modelocking of THz QCLs. Finally, a new phenomenon is presented where the modes of a free running THz QCL can beat together to generate free space microwave emission
39
Weisz, Mario. "Electrothermal device-to-circuit interactions for half THz SiGe∶C HBT technologies". Thesis, Bordeaux 1, 2013. http://www.theses.fr/2013BOR14909/document.
Resumen
Ce travail concerne les transistors bipolaires à hétérogène TBH SiGe. En particulier, l'auto-échauffement des transistors unitaires et le couplage thermique avec leurs plus proches voisins périphériques sont caractérisés et modélisés. La rétroaction électrothermique intra- et inter-transistor est largement étudiée. En outre, l’impact des effets thermiques sur la performance de deux circuits analogiques est évalué. L'effet d'autoéchauffement est évalué par des mesures à basse fréquence et des mesures impulsionnelles DC et AC. L'auto-échauffement est diminué de manière significative en utilisant des petites largeurs d'impulsion. Ainsi la dépendance fréquentielle de l’autoéchauffementa été étudiée en utilisant les paramètres H et Y. De nouvelles structures de test ont été fabriqués pour mesurer l'effet de couplage. Les facteurs de couplage thermique ont été extraits à partir de mesures ainsi que par simulations thermiques 3D. Les résultats montrent que le couplage des dispositifs intra est très prononcé. Un nouvel élément du modèle de résistance thermique récursive ainsi que le modèle de couplage thermique a été inclus dans un simulateur de circuit commercial. Une simulation transitoire entièrement couplée d'un oscillateur en anneau de 218 transistors a été effectuée. Ainsi, un retard de porte record de 1.65ps est démontré. À la connaissance des auteurs, c'est le résultat le plus rapide pour une technologie bipolaire. Le rendement thermique d'un amplificateur de puissance à 60GHz réalisé avec un réseau multi-transistor ou avec un transistor à plusieurs doigts est évalué. La performance électrique du transistor multidoigt est dégradée en raison de l'effet de couplage thermique important entre les doigts de l'émetteur. Un bon accord est constaté entre les mesures et les simulations des circuits en utilisant des modèles de transistors avec le réseau de couplage thermique. Enfin, les perspectives sur l'utilisation des résultats sont donnéesThe power generate by modern silicon germanium (SiGe) heterojunction bipolar transistors (HBTs) can produce large thermal gradients across the silicon substrate. The device opering temperature modifies model parameters and can significantly affect circuit operation. This work characterizes and models self-heating and thermal coupling in SiGe HBTs. The self-heating effect is evaluated with low frequency and pulsed measurements. A novel pulse measurement system is presented that allows isothermal DC and RF measurements with 100ns pulses. Electrothermal intra- and inter-device feedback is extensively studied and the impact on the performance of two analog circuits is evaluated. Novel test structures are designed and fabricated to measure thermal coupling between single transistors (inter-device) as well as between the emitter stripes of a multi-finger transistor (intra-device). Thermal coupling factors are extracted from measurements and from 3D thermal simulations. Thermally coupled simulations of a ring oscillator (RO) with 218 transistors and of a 60GHz power amplifier (PA) are carried out. Current mode logic (CML) ROs are designed and measured. Layout optimizations lead to record gate delay of 1.65ps. The thermal performance of a 60GHz power amplifier is compared when realized with a multi-transistor array (MTA) and with a multi-finger trasistor (MFT). Finally, perspectives of this work within a CAD based circuit design environment are discussed
40
Pearce, Jeremiah Glen. "Multiple scattering of broadband terahertz pulses". Thesis, 2005. http://hdl.handle.net/1911/18797.
Resumen
Propagation of single-cycle terahertz (THz) pulses through a random medium leads to dramatic amplitude and phase variations of the electric field because of multiple scattering. We present the first set of experiments that investigate the propagation of THz pulses through scattering media. The scattering of short pulses is a relevant subject to many communities in science and engineering, because the properties of multiply scattered or diffuse waves provide insights into the characteristics of the random medium. For example, the depolarization of diffuse waves has been used to form images of objects embedded in inhomogeneous media.
Most of the previous scattering experiments have used narrowband optical radiation where measurements are limited to time averaged intensities or autocorrelation quantities, which contain no phase information of the pulses. In the experiments presented here, a terahertz time-domain spectrometer (THz-TDS) is used. A THz-TDS propagates single-cycle sub-picosecond pulses with bandwidths of over 1 THz into free space. The THz-TDS is a unique tool to study such phenomena, because it provides access to both the intensity and phase of those pulses through direct measurement of the temporal electric field. Because of the broad bandwidth and linear phase of the pulses, it is possible to simultaneously study Rayleigh scattering and the short wavelength limit in a single measurement.
We study the diffusion of broadband single-cycle THz pulses by propagating the pulses through a highly scattering medium. Using the THz-TDS, time-domain measurements provide information on the statistics of both the amplitude and phase of the diffusive waves. We develop a theoretical description, suitable for broadband radiation, which accurately describes the experimental results. We measure the time evolution of the degree of polarization, and directly correlate it with the single-scattering regime in the time domain. Measurements of the evolution of the temporal phase of the radiation demonstrate that the average spectral content depends on the state of polarization. In the case of broadband radiation, this effect distinguishes photons that have been scattered only a few times from those that are propagating diffusively.
41
Mitrofanov, Oleg. "Near-field imaging with terahertz pulses". Thesis, 2001. http://library1.njit.edu/etd/fromwebvoyage.cfm?id=njit-etd2001-079.
42
Pearce, Jeremiah Glen. "The propagation of single-cycle terahertz pulses in random media". Thesis, 2002. http://hdl.handle.net/1911/17538.
Resumen
We describe what are to our knowledge the first measurements of the propagation of coherent, single-cycle pulses of terahertz radiation in a scattering medium. We measure the propagation constants for pulses in a dense collection of spherical scatterers, and compare to the predictions of the quasi-crystalline approximation. Even though the fractional volume in our measurements exceeds the limit of validity of this model, we find that it still predicts certain features of the propagation with reasonable accuracy. By measuring the transmission as a function of the length L of the medium, we extract the scattering mean free path lambdasc (o) over a broad bandwidth. We observe variations in lambda sc ranging over nearly two orders of magnitude, and covering the entire thin sample regime from L/lambda sc << 1 to L/lambdasc ∼10.
43
Lu, Shi-Hsiang y 呂世香. "The generation of terahertz electromagnetic pulses: generation properties and efficiency". Thesis, 2001. http://ndltd.ncl.edu.tw/handle/15523576152918784339.
Resumen
博士國立清華大學
電機工程學系
89
The generation and detection of THz radiation by a sub-picosecond (1 ps = 10e-12 sec) laser source has become a fast growing field since the 1980’s, due to its promising scientific and engineering applications. Yet many efforts are still required to clarify the underlying mechanism of THz radiation and to increase the emitting efficiency and bandwidth. In this dissertation, we investigate three commonly used THz emitters, i.e. photoconductive antennas, semiconductors under magnetic fields, and quantum well emitters. As to investigation of THz emitters, we also proposed a calculation scheme to analyze the THz radiation from quantum wells. Three types of GaAs-based materials, including semi-insulated GaAs (SI-GaAs), low-temperature GaAs deposited on SI-GaAs (LT-GaAs), low-temperature GaAs deposited on sapphire (LT-OS), which represent three crystallinty, are used to be the photoconductors of large-aperture photoconductive antennas (LAPAs). Among these three materials, because of its crystallinity, SI-GaAs has the largest carrier mobility, and hence the largest radiated field, which is ~2.5 times larger than that from LT-GaAs, and ~18 times larger than LT-OS. On the other hand, the lower carrier lifetimes of LT-GaAs and LT-OS induce slightly higher bandwidth in THz radiation. Therefore, there is a trade-off between the bandwidth and the intensity of THz radiating field. For these three materials, the radiating amplitudes are linearly proportional to the laser powers and externally biased electric fields. Moreover, the carrier mobility extracted from measured THz radiation is roughly consistent with the estimated value from photocurrent, time-resolved phototransmission, and electrical pulse measurements. This finding indicates that photoconduction is the dominant mechanism for THz radiation from LAPAs. In additional to conventional dipole antenna structure, we also measured THz radiation from a spiral antenna, and found highly dispersive THz waveforms, which indicate that the antenna structures strongly affect the waveforms of radiated field. The THz radiation from a spiral antenna exhibits obviously different waveforms in comparison with LAPA’s. In addition, by a novel nearly-filled-gap nonuniform illumination scheme, we found very short electrical pulses (FWHM∼190 fs) can be generated on a coplanar transmission line. The measured THz radiation from semiconductors under magnetic field consists of two components, one is from surface depletion field, and another is from carrier motion driven by magnetic field. The surface depletion field plays a role to “trigger” the carrier motion under magnetic field. Therefore, for a semiconductor under magnetic field, the amplitude of radiation field is proportional to surface depletion field. The other factors affecting the amplitude of radiation field include the effective mass and the applied magnetic field. At the same magnetic field, the measured amplitude from several semiconductors, including undoped InAs, n-doped InAs, SI-GaAs and InSb is proportional to their surface depletion field and inversely proportional to their effective mass. The measured THz beam profile indicates that the diverging angle of THz radiation beam from InAs under magnetic field is about 24°, and the radiation beam is not emitted along the specular direction of the pump beam. There is about 6° deviation between it. Therefore, the misalignment of THz beams must be carefully taken into account to utilize this type of emitters. Quantum-well THz emitters are relatively attractive for their adjustable radiating frequency. To design the optimal structure of a quantum well emitter, we propose a general k×p-type multiband transfer-matrix energy-band calculation method, which is efficient and can be generally employed in the calculation of the band structures of two-dimensional semiconductor systems. Strain, electric field, and magnetic field can all be incorporated in a unified manner. Our calculated results are consistent with those reported in the literature. With this multiband transfer-matrix method, the envelope functions as well as the in-plane dispersion relationship can be obtained, and all the remote bands can be included. Therefore, this approach is an appropriate tool for investigating the coupling effect between bands, which is important in the case of low-energy band gap or strong spin-orbit-coupling materials. Based on the calculated results of electronic states, the approach was employed to calculate THz radiation from quantum wells and the results are consistent with the results in the literature. Therefore, it is expected that the calculation approach is useful to analyze and to optimize THz radiation from quantum-well emitters. Moreover, we also measured and analyzed THz radiation from two-dimensional semiconductor structures. For the THz radiation from a p-i-n multiple quantum well, the coupling between wells are weak due to the thick barrier between them; therefore the charge oscillation disappears. In addition, due to the carrier motion interfered by barrier; the applied magnetic field parallel to the layer does almost not affect the THz radiation. The THz radiation from a modulation-doped heterostructure consists of two components; one is from surface depletion field, the other is from the applied magnetic field. This property is similar to some bulk semiconductors.
44
Cheng, Chen Yu y 鄭宸語. "The Studies of Two Methods for Generation of Stronger Terahertz Pulses". Thesis, 2015. http://ndltd.ncl.edu.tw/handle/8xda6e.
Resumen
碩士國立清華大學
光電工程研究所
103
In this work, we studied two methods to generate stronger THz pulses: (1) by tilted-pulse-front pumping in highly-doped stoichiometric lithium niobate (sLN) and (2) by optical rectification (OR) in ZnTe by using dual-color pulses. Firstly, we build up the system with 5 mol% Mg: sLN. When this unique source was applied in THz-TDS, it can increase signal-noise ratio in sub-THz region, such as the extraction of the optical constant of Teflon and fused silica to 50 GHz. Further, the saturation effect which limits efficiency of THz generation can be much more unobvious than from the sLN with small Mg doping level with negligible increase of THz absorption in 0.1-1.5 THz region. Our explanation is that more phonons are scattered by the more defects in the highly-doped crystal. However, THz phonon-polaritons decay into pair of phonons. But, the less number of the phonons decreases the decay rate of the THz polaritons. Besides, to explore the possibility of enhancement in THz generation, we demonstrate the experimental and theoretical THz pulses generation by applying OR in ZnTe crystal semiconductor with coherent-controlled two-color laser. The phase inverse phenomenon of THz signals generated by fundamental wave (FW) and the second harmonic (SH) pulses can be observed. With different power ratios and delay times between two-color pulses, the competition of the THz generations between FW and SH pulses was revealed. The possible explanation of the competition is that the shift current which is one of the OR process is modulated by the different color pulse. Since the shift current is established by the excitation of the photons whose energy is above the energy bandgap of crystal and the state of the electromagnetic field of same frequency wave, the SH pulses whose photon energy is below energy bandgap also affect the generation of the shift current. Consequently, the shift current is reduced by the different color pulses.
45
Hu, Wei-Zhe y 胡偉哲. "Investigation on Generation of terahertz radiation from a gas plasma excited by phase-controlled multi-color ultrafast pulses". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/cz8868.
46
"Medical terahertz pulsed Imaging in reflection geometry". Thesis, 2009. http://library.cuhk.edu.hk/record=b6075421.
Resumen
Huang, Shengyang.Thesis (Ph.D.)--Chinese University of Hong Kong, 2009.
Includes bibliographical references (leaves 100-108).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstract also in Chinese.
47
Wang, Chao-Kai y 王昭凱. "Simulation of Terahertz pulse generation by noise like pulse". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/q2tr3b.
48
"Terahertz pulsed imaging of osteoarthritis joint cartilage". 2010. http://library.cuhk.edu.hk/record=b5894273.
Resumen
Kan, Wai Chi.Thesis (M.Phil.)--Chinese University of Hong Kong, 2010.
Includes bibliographical references (p. 111-116).
Abstract --- p.i
Acknowledgement --- p.iii
List of Publications --- p.vi
List of Figures --- p.xi
List of Tables --- p.xii
Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- Terahertz Radiation --- p.1
Chapter 1.2 --- Biomedical Applications of Terahertz Imaging --- p.3
Chapter 1.3 --- THz Spectroscopy --- p.4
Chapter 1.4 --- Osteoarthritis --- p.4
Chapter 1.5 --- Aim and motivation --- p.5
Chapter 1.6 --- Overview of thesis --- p.5
Chapter 2 --- Theory --- p.7
Chapter 2.1 --- Propagation of electromagnetic field through dielectric media --- p.7
Chapter 2.2 --- Deconvolution --- p.10
Chapter 2.3 --- Baseline offset --- p.12
Chapter 2.4 --- Frequency-dependent Refractive Index and Absorption Coefficient --- p.15
Chapter 2.4.1 --- Reflection Geometry --- p.15
Chapter 2.4.2 --- Transmission Geometry --- p.17
Chapter 2.5 --- Conversion of Optical Delay into Depth --- p.22
Chapter 2.6 --- Finite Difference Time Domain Method --- p.23
Chapter 2.7 --- Summary --- p.25
Chapter 3 --- Terahertz Systems --- p.26
Chapter 3.1 --- Terahertz Pulsed Generation --- p.26
Chapter 3.2 --- Terahertz Pulsed Detection --- p.28
Chapter 3.3 --- Terahertz Pulsed Imaging (TPI) System --- p.29
Chapter 3.4 --- Reflection System --- p.29
Chapter 3.4.1 --- Flatbed System --- p.29
Chapter 3.4.2 --- Probe --- p.32
Chapter 3.5 --- Transmission System --- p.36
Chapter 3.5.1 --- Antenna --- p.39
Chapter 3.6 --- Data Acquisition --- p.40
Chapter 3.6.1 --- Flatbed System --- p.40
Chapter 3.6.2 --- Probe --- p.42
Chapter 3.7 --- Baseline Validation --- p.46
Chapter 4 --- Osteoarthritis --- p.48
Chapter 4.1 --- Introduction --- p.48
Chapter 4.2 --- Cartilage Composition and Structure --- p.49
Chapter 4.3 --- 〇A symptoms --- p.51
Chapter 4.4 --- Other Imaging Techniques --- p.52
Chapter 4.5 --- Sample Preparation and Histology --- p.54
Chapter 5 --- THz Pulsed Imaging of OA --- p.58
Chapter 5.1 --- Results --- p.58
Chapter 5.1.1 --- Optical Delays --- p.59
Chapter 5.1.2 --- Estimation of surface refractive index --- p.69
Chapter 5.1.3 --- Conversion of Optical Delay into Cartilage Thickness --- p.72
Chapter 5.1.4 --- Correlation with Histology --- p.74
Chapter 5.1.5 --- Errors and Problems --- p.80
Chapter 5.2 --- FDTD of cartilage layers --- p.85
Chapter 5.3 --- Conclusion --- p.87
Chapter 6 --- Sliced Cartilage Sample and Bone Measurement --- p.88
Chapter 6.1 --- Sliced Cartilage Samples --- p.88
Chapter 6.1.1 --- Multi-reflections of sliced cartilage samples --- p.89
Chapter 6.1.2 --- The influence of pressure on cartilage thickness --- p.91
Chapter 6.1.3 --- Estimation of surface refractive index of sliced cartilage samples --- p.93
Chapter 6.1.4 --- Comparison between sliced cartilage and knee joint measurements --- p.95
Chapter 6.2 --- Bone --- p.97
Chapter 7 --- Transmission System Result --- p.99
Chapter 7.1 --- Data Validation --- p.99
Chapter 7.1.1 --- Water spectrum --- p.99
Chapter 7.1.2 --- Quartz measurement --- p.100
Chapter 7.2 --- Liquid cell --- p.100
Chapter 7.3 --- Cartilage Transmission Result --- p.103
Chapter 7.4 --- Difficulties and problems --- p.105
Chapter 7.5 --- Conclusions --- p.106
Chapter 8 --- Conclusions and future work --- p.107
Chapter 8.1 --- Summary --- p.107
Chapter 8.2 --- Discussion --- p.107
Chapter 8.3 --- Suggestions for further study --- p.109
Bibliography --- p.111
49
"Investigating biomolecular interactions using terahertz pulsed spectroscopy". Thesis, 2010. http://library.cuhk.edu.hk/record=b6075253.
Resumen
Finally, based on theoretical calculations and experiments, we present a development model (DDRA model) to describe the interaction between the protein and its solvent molecule. The parameters derived from this model provide good fits to the experimentally determined complex dielectric constant, making it of the model valuable benchmarks for other theoretical treatments of bio-molecular system.Secondly, we focus our aims on investigating protein molecules due to the possibility of being able to explain the mechanism of molecular interactions more clearly. Two lands of labeled immunoglobulin G were investigated using a reflective THz-IDS system. The dielectric properties were sensitive to the conjugation of the antibody. Additionally, terahertz spectroscopy is able to evaluate the depth of the hydrogen shell and shows that the hydrogen-bonded networks of charged protein solutions play an important role in determining the dielectric.
The bio-molecular interaction has been one of the most challenging subjects to probe due to its complexity. In the thesis, we have been attempting to answer fundamental questions about bio-molecular interactions in the terahertz (THz) region from the macroscopic to microscopic level. Terahertz radiation (defined as 0.1--10 THz) can excite intermolecular interactions such as the librational and vibrational modes. These attributes make it feasible to probe the dynamic characteristics of the bio-molecular system. Furthermore, it is worth investigating whether terahertz technology could potentially be used as a novel tool in the biomedical diagnosis field in the near future.
Thirdly, using a transmission THz-TDS system we investigated a biomarker protein and observed distinct spectral differences at various temperatures. This work demonstrates that terahertz spectroscopy can be used to evaluate the anharmonicity of the vibrational potential. By comparing the absorption spectra of the THz-TDS and Synchrotron results it is possible to deduce the approximate localization of the vibrational modes within the molecular chain.
We develop a controlled study to investigate the effects of formalin fixing on the THz properties of two different tissue types. The optical properties are measured using THz reflection spectroscopy. The results present how the fixing process can affect image contrast in THz images of biological samples.
Sun, Yiwen.
Advisers: Emma MacPherson; Yuan-ting Zhang.
Source: Dissertation Abstracts International, Volume: 73-03, Section: B, page: .
Thesis (Ph.D.)--Chinese University of Hong Kong, 2010.
Includes bibliographical references (leaves 120-140).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstract also in Chinese.
50
Young, Christopher Dall. "Exploring terahertz pulse enhancement through gold nanoparticle deposition". 2009. http://digital.library.okstate.edu/etd/Young_okstate_0664M_10334.pdf.