Дисертації: "Pulsed laser radiation"

1

Choi, Bernard. "Thermal interactions of pulsed laser radiation and cryogen spray cooling with skin." Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3025203.

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2

Афанасьева, О. В., Ю. П. Мачехин, Н. А. Лалазарова та Т. Ю. Свергун. "Термическая обработка быстрорежущих сталей с помощью лазеров малой мощности". Thesis, ХНУРЭ, 2011. http://openarchive.nure.ua/handle/document/9125.

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Надежность и долговечность инструмента из быстрорежущей стали в основном определяется его твердостью, которая зависит от химического состава и режимов термической обработки. Поэтому целью данной работы является разработка режимов лазерной закалки для быстрорежущей стали, обеспечивающих максимальную твердость.

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3

Афанасьева, О. В., та Ф. А. Евтушенко. "Разработка режимов лазерной резки неметаллов". Thesis, «Бял ГРАД-БГ», 2017. http://openarchive.nure.ua/handle/document/9245.

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4

Афанасьева, О. В., та М. В. Патлань. "Лазерные технологии обработки неметаллических материалов". Thesis, Sheffield. Science and education LTD, 2019. http://openarchive.nure.ua/handle/document/9248.

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5

Romano, Valerio. "Interaction of pulsed laser radiation with tissue : determination of the thermal damage with time resolved thermal microscopy /." Bern, 1991. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.

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6

Афанасьева, О. В., та Н. А. Лалазарова. "Влияние импульсной лазерной обработки на свойства инструментальных сталей". Thesis, ХНАДУ, 2016. http://openarchive.nure.ua/handle/document/9249.

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Целью настоящей работы является разработка режимов упрочнения поверхности деталей и инструмента с использованием YAG-лазеров малой мощности. Исследования проводились на инструментальных сталях: углеродистой и быстрорежущей, после стандартной термической обработки. Основным варьируемым параметром была длительность импульса В качестве параметра контроля свойств упрочненного слоя была выбрана микротвердость. Было показано, что для каждой стали существует оптимальное значение длительности импульса, обеспечивающее максимальную твёрдость.

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7

Tadadjeu, Sokeng Ifriky. "Sub-10 MeV proton irradiation effects on a coating obtained from the pulsed laser ablation of W2B5/B4C for space applications." Thesis, Cape Peninsula University of Technology, 2015. http://hdl.handle.net/20.500.11838/2181.

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Thesis submitted in partial fulfilment of the requirements for the degree Doctor of Technology: Electrical, Electronic and Computer Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology
This research investigates the effects of sub-10 MeV protons on coatings obtained from the pulsed laser ablation of W2B5/B4C. This is in an attempt to extend the bullet proof applications of W2B5/B4C to space radiation shielding applications, offering low cost and low mass protection against radiation including X-rays, neutrons, gamma rays and protons in low Earth orbit. The focus in this research, however, is on low energy protons. The associated problems addressed in this work are solar cell degradation and Single Event Upsets in high density semiconductor devices caused by low energy protons. The relevant constraints considered are the necessity for low cost, low mass and high efficiency solutions. The work starts with a literature review of the space environment, the interaction of radiation with matter, and on pulsed laser deposition as a technique of choice for the coating synthesis. This paves the way for the pulsed laser ablation of W2B5/B4C. The resulting coating is a solid solution of the form WC1-xBx which contains crystalline and amorphous forms. Two proton irradiation experiments are carried out on this coating, and the resulting effects are analysed. The effects of 900 keV proton irradiation were the melting and subsequent growing of nanorods on the surface of the coating, the lateral transfer of the proton energy across the coating surface, and the lateral displacement of matter along the coating surface. These effects show that the coating is a promising cost effective and low mass radiation shield against low energy protons. The effects of 1 MeV protons on this coating are the three-stage melting of rods formed on the coating surface, and further evidence of lateral transfer of energy across the coating surface. Optical measurements of this coating show that it is about 73% transparent in the Ultraviolet, Visible and near Infrared range. This allows it to be used as radiation shielding for solar cells, in addition to high density semiconductor devices, against low energy protons in low Earth orbit. Simulations show that based on coulombic interactions alone, the same level of protection coverglass offers to solar cells can be achieved with about half the thickness of WC1-xBx or less.

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8

COUTANCE, PASCAL. "Etude du laser cu/hbr. Son application au pompage d'une chaine laser sa/ti." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10253.

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Un laser cu/hbr de plus de 100 watts a 18 khz avec un rendement a la prise de 1. 4% a ete construit au laboratoire. Nous l'avons caracterise au niveau des performances et de la qualite de faisceau. Nous avons montre que son profil d'intensite en champ lointain est parfaitement symetrique et quasi-gaussien avec une divergence de 3 fois la limite de diffraction en cavite instable axiale contrairement au profil d'un laser a vapeur de cuivre classique. Une simulation nous permet de retrouver les caracteristiques du champ lointain pour le laser cu/hbr et de montrer, avec l'appui de nos resultats experimentaux, qu'une cavite instable de grandissement 40 est un bon compromis entre puissance et qualite de faisceau. Nous avons effectue des mesures de cinetique d'especes presentes dans le laser cu/hbr. Nous avons mesure pour la premiere fois la concentration des molecules cubr et cu#3br#3 aussi bien radialement que temporellement dans le laser. Ces mesures montrent que la source principale d'atomes de cuivre dans ce laser est la molecule cu#3br#3 et non cubr comme il etait admis jusque la. Nous avons utilise le laser cu/hbr afin de pomper une chaine laser composee d'un oscillateur et d'un amplificateur sa/ti afin d'obtenir une source proche infrarouge, spectralement fine, de forte puissance et pulsee a 18 khz qui sera utilisee pour des experiences de spectroscopie. Nous avons obtenu ainsi un oscillateur avec une cavite en z sortant 300 mw a 795 nm avec 10% de rendement optique, a un taux de repetition de 18 khz, de largeur spectrale 3 ghz et balayable sur 40 cm#-#1. Nous avons amplifie le faisceau grace a deux passages dans un amplificateur sa:ti et obtenu ainsi 1. 4 watts. Ce travail a permis de modeliser un futur systeme de forte puissance

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9

BERGEON, MURIELE. "Etude et realisation de microlasers declenches et de microlasers balayes en longueur d'onde, compatibles avec un procede de fabrication collectif." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10248.

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Le microlaser est un laser a etat solide miniature (<1mm#3), dont les miroirs de la cavite sont directement deposes sur le milieu a gain. De nombreuses applications demandent un fonctionnement impulsionnel ou balaye en longueur d'onde (telemetrie, detection de gaz, marquage). En inserant un cristal electrooptique a l'interieur de la cavite laser, des microlasers a emission declenchee et des microlasers a emission balayee en longueur d'onde ont ete realises. Les dispositifs concus sont constitues de yag:nd et de tantalate de lithium, ils sont stabilises en temperature et donnent une emission laser a 1,06 m. Le declenchement de ces microlasers a donne des impulsions laser de 0,3 j d'energie, a des frequences de 5 a 10 khz pour un champ electrique appliquee de 0,8 10#6 v/m. De meme, le balayage de la longueur d'onde laser est realise avec un taux de balayage de 10 mhz/v, a des frequences variant du continu jusqu'a 20 khz: des excursions de 10 ghz (0,35 a) ont ete mesurees pour un champ electrique de 10#6 v/m. De maniere a maintenir les qualites de compacite et fiabilite intrinseques au microlaser, un procede de fabrication collectif a ete mis au point

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10

BERRETTA, JOSE R. "Solda laser em materiais dissimilares com laser de Nd:YAG pulsado." reponame:Repositório Institucional do IPEN, 2005. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11293.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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11

MACHADO, LEANDRO M. "Microusinagem de dielétricos com pulsos laser de femtossegundos." reponame:Repositório Institucional do IPEN, 2012. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10119.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
FAPESP:08/00284-0

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12

Obozna, V. P., and О. S. Hnatenko. "Formation of Laser Radiation Pulses for Encoding inFormation." Thesis, Sumy State University, 2018. http://essuir.sumdu.edu.ua/handle/123456789/67954.

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The main purpose of this work is to study the characteristics of the sequence of output pulses and the distances between the peaks of the pulses of the output radiation of a ring fiber femtosecond laser with nonlinear evolution of mode polarization for encoding information on the phase of pulses. An example of coding information for the phase of pulses is figure 1, which shows the pulse sequence corresponding to the number 101010010100 in the binary system, which is 2708 in the decimal system.

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13

Obozna, V. P., and O. S. Hnatenko. "Formation of Laser Radiation Pulses for Encoding in Formation." Thesis, Sumy State University, 2018. http://openarchive.nure.ua/handle/document/6804.

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The main purpose of this work is to study the characteristics of the sequence of output pulses and the distances between the peaks of the pulses of the output radiation of a ring fiber femtosecond laser with nonlinear evolution of mode polarization for encoding information on the phase of pulses. An example of coding information for the phase of pulses is figure 1, which shows the pulse sequence corresponding to the number 101010010100 in the binary system, which is 2708 in the decimal system.

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14

Edwards, Michael John. "Radiation transport and short pulse interaction in laser irradiated targets." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46288.

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15

Melninkaitis, Andrius. "Optical resistance of dielectric coatings to multi-pulse femtosecond laser radiation." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2009~D_20090408_085213-11247.

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The present Ph.D. thesis is the experimental and theoretical analysis of the femtosecond laser pulse induced damage processes in thin film dielectric coatings. Experimental investigations were performed by automated metrological facility designed for S-on-1 laser-induced damage threshold measurements. Femtosecond repetitive pulses (1 kHz) either at fixed 800 nm and 400 nm wavelengths or continuously tunable in 590 nm to 750 nm spectral range were used. The sensitivity of assembled metrological facility was sufficient to determine the influence of various deposition factors (process parameters and coating materials) on LIDT of optical coatings. Our experimental investigations on multi-layer ZrO2/SiO2, HfO2/SiO2, Ta2O5/SiO2, TiO2/SiO2 high reflection coatings and single-layer TiO2 have yielded several important results. To summarize: stepwise change of LIDT values was experimentally observed at the wavelength where two-photon absorption changes to three-photon absorption. This confirms that multiphoton absorption is one of the main damage mechanisms in femtosecond range. The multilayer coatings deposited by IAD and e-beam techniques on substrates having roughness of 0.64 nm or smaller showed similar LIDT values. Moreover, it was also confirmed that suppressing of standing wave electric field intensity at the outer layers of high refractive index improves the optical resistance of high reflectivity coatings also for femtosecond pulses. Furthermore, the model of the... [to full text]
Pagrindinis šio darbo tikslas - eksperimentiškai ir teoriškai išnagrinėti fundamentinius bei technologinius veiksnius, apribojančius dielektrinių dangų optinį atsparumą pasikartojantiems femtosekundinės trukmės lazerio impulsams. Specialiai šiems tyrimams atlikti buvo sukurta automatizuota eksperimentinė įranga, kuri pagreitino pažeidimo slenksčio matavimus ir minimizavo žmogiškąjį faktorių. Darbo metu eksperimentiškai buvo tiriamos tiek vienasluoksnės TiO2, tiek ir didelio atspindžio koeficiento daugiasluoksnės ZrO2/SiO2, HfO2/SiO2, Ta2O5/SiO2 bei TiO2/SiO2 dangos, padengtos skirtingais būdais. Pirmą kartą eksperimentiškai pademonstruota, kad dėl daugiafotonės sugerties įtakos dielektrinių dangų pažeidimo slenkstis, tolydžiai keičiant femtosekundinių impulsų bangos ilgį, kinta šuoliškai. Kartu pademonstruotos ir teorinės šio rezultato prielaidos. Eksperimentiškai pademonstruota, kad didelio atspindžio koeficiento dangose stovinčiosios elektromagnetinės bangos pūpsnius „perstūmus“ į žemesnio lūžio rodiklio sluoksnius padidėja optinis atsparumas ir femtosekundinei lazerinei spinduliuotei. Taip pat eksperimentiškai buvo nustatyti įvairių dangų, dengtų jonapluoščio dulkinimo, elektronpluoščio nusodinimo su papildomu jonų tankinimu ir be jo technologijomis, pažeidimo slenksčiai įvairios trukmės ir įvairių bangos ilgių femtosekundiniams impulsams. Teoriškai išnagrinėtas vadinamojo S-į-1 pažeidimo tikimybės matavimo atvejis, kai lazerinės spinduliuotės erdviniai ir energetiniai... [toliau žr. visą tekstą]

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16

Mackenroth, Kai Felix [Verfasser], and Piazza Antonino [Akademischer Betreuer] Di. "Quantum radiation in ultra-intense laser pulses / Kai Felix Mackenroth ; Betreuer: Antonino Di Piazza." Heidelberg : Universitätsbibliothek Heidelberg, 2012. http://d-nb.info/1177040328/34.

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17

El, Akel Azad. "Étude du rayonnement transitoire unidimensionnel en utilisant la méthode des ordonnées discrétes [i.e. discrètes] /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 2004. http://theses.uqac.ca.

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18

Plumridge, Jonathan. "Multielectron dissociation and ionization of small molecules probed by intense laser fields." Thesis, University of Reading, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343322.

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19

Bergh, Magnus. "Interaction of Ultrashort X-ray Pulses with Material." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8274.

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20

Hjelte, Ingela. "Temporal Studies of Molecular Processes using Resonant Spectroscopy : Femtosecond experiments with synchrotron radiation and pulsed lasers." Doctoral thesis, Uppsala University, Department of Physics, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3079.

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The physical and chemical properties of matter are to a high degree determined by the electronic structure. One of the most powerful experimental techniques to study the electronic structure is electron spectroscopy. Conventionally most of the investigations on molecules, carried out using this technique, have dealt with static information such as binding energies and localization of the electron. This thesis focuses on the currently expanding field more concerned with dynamic effects such as lifetimes and dissociation times. In particular, resonantly excited molecules have been studied.

As an example, we have used the "core hole clock" method to determine the dissociation times of core excited water and ammonia molecules. These experiments are possible using a synchrotron light source and the experiments are based on ultra-fast dissociation of resonantly excited states. A similar experiment on doubly core-excited nitrogen molecules have revealed no sign of ultra-fast dissociation as the resulting spectral features contain vibrational progressions and therefore result from molecular decay.

Molecules that dissociate on an ultra-fast timescale, i.e. in the low femtosecond regime, are interesting for several reasons. For instance, decay occurring in core excited oxygen fragments can be used to demonstrate a localization of the core hole through the existence of a Doppler effect. Also, the nature of the molecular intermediate state leading to ultra-fast dissociation can be of interest. For the oxygen molecule there is a debate concerning the assignment of the large absorption structure near the O1s ionization energy. We are able to disclose which photon wavelengths lead to ultra-fast dissociation.

Direct information on the time dependence of electronic structure and molecular dynamics during the ionization process can be obtained through the use of fast pulsed lasers in pump-probe experiments. For such studies we have used the terawatt laser at the Lund Laser Center providing pulses down to 110 fs long to observe the decay of two different states in valence excited acetylene.

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21

Gonoskov, Arkady. "Ultra-intense laser-plasma interaction for applied and fundamental physics." Doctoral thesis, Umeå universitet, Institutionen för fysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-84245.

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Rapid progress in ultra-intense laser technology has resulted in intensity levels surpassing 1022 W/cm2, reaching the highest possible density of electromagnetic energy amongst all controlled sources available in the laboratory. During recent decades, fast growth in available intensity has stimulated numerous studies based on the use of high intensity lasers as a unique tool for the initiation of nonlinear behavior in various basic systems: first molecules and atoms, then plasma resulting from the ionization of gases and solids, and, finally, pure vacuum. Apart from their fundamental importance, these studies reveal various mechanisms for the conversion of a laser pulse's energy into other forms, opening up new possibilities for generating beams of energetic particles and radiation with tailored properties. In particular, the cheapness and compactness of laser based sources of energetic protons are expected to make a revolution in medicine and industry. In this thesis we study nonlinear phenomena in the process of laser radiation interacting with plasmas of ionized targets. We develop advanced numerical tools and use them for the simulation of laser-plasma interactions in various configurations relating to both current and proposed experiments. Phenomenological analysis of numerical results helps us to reveal several new effects, understand the physics behind them and develop related theoretical models capable of making general conclusions and predictions. We develop target designs to use studied effects for charged particle acceleration and for the generation of attosecond pulses of unprecedented intensity. Finally, we analyze prospects for experimental activity at the upcoming international high intensity laser facilities and uncover a basic effect of anomalous radiative trapping, which opens up new possibilities for fundamental science.

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22

Gaillard, Romain Philippe. "The interaction of picosecond high intensity laser pulses with preformed plasmas and solid targets." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313744.

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23

Clayson, Thomas. "Experimental study of radiative shocks in noble gases on the Orion laser and the MAGPIE pulsed-power facility." Thesis, Imperial College London, 2018. http://hdl.handle.net/10044/1/62624.

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This Thesis introduces two novel experimental configurations for studying radiative shocks with the aim of improving our understanding of the physics involved, which is relevant to laboratory astrophysics, inertial confinement fusion and for benchmarking numerical simulations. Experiments on the Orion laser facility used lasers with an intensity of 5x10^14 W/cm^2 to drive counter-propagating shocks, with a velocity of 60 km/s, into a gas-fill (of Neon, Argon, Krypton or Xenon) with an initial mass density of 0.5 to 1.6 mg/cm^3. These experiments simultaneously study both the post-shock material and radiative precursor for the first time, with a combination of X-ray backlighting, self-emission streaked imaging and laser interferometry. Experiments with Neon gas-fills allowed for post-shock compression measurements, x23, and the counter-propagating shock configuration allowed reverse shocks to be studied. In addition, large gas-cells allowed for shocks to evolve in three dimensions, resulting in the formation of post-shock instabilities which will be the subject of future work. Experiments on the MAGPIE generator introduce the 'inverse liner z-pinch', building upon previous experiments on imploding liners where diagnostic access was limited and radiative effects occurred on spatial scales larger than the experiment. A 1 MA current pulse was passed through a liner embedded in a gas-fill (of Neon, Argon, Krypton or Xenon), with an initial mass density of 0.04 mg/cm^3, and returned through a central post. This launched a cylindrically expanding radiative shock which propagated at 10 km/s. Experiments were diagnosed with a combination of self-emission imaging, laser interferometry and optical emission spectroscopy. Shocks were able to propagate for several centimetres, allowing the ionization in the radiative precursor to be measured, which was not possible in previous experiments. Future work will use this platform to study radiative shocks with perturbations by introducing well characterised grooves on the surface of the liner.

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24

CORDEIRO, THIAGO da S. "Controle das características geométricas de nanopartículas de prata através da conformação temporal de pulsos ultracurtos utilizando algoritmos genéticos." reponame:Repositório Institucional do IPEN, 2013. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10550.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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25

SICCHIERI, LETICIA B. "Caracterização da lipoproteína de baixa densidade (LDL) por meios espectroscópicos." reponame:Repositório Institucional do IPEN, 2012. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10109.

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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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26

PETRI, ANNA R. "Medidas do primeiro coeficiente de Townsend de ionização no isobutano puro submetido a campos elétricos uniformes." reponame:Repositório Institucional do IPEN, 2013. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10198.

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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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27

FRESCHI, LARISSA R. "Determinação do limiar de ablação de resina composta e amálgama utilizando laser de pulsos ultracurtos." reponame:Repositório Institucional do IPEN, 2007. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9978.

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Dissertacao (Mestrado Profissionalizante em Lasers em Odontologia)
IPEN/D-MPLO
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP; Faculdade de Odontologia, Universidade de Sao Paulo, Sao Paulo

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28

POLI, VLADIMIR D. "Estudo da interação de pulsos de femtossegundos com o tecido ósseo." reponame:Repositório Institucional do IPEN, 2006. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11705.

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Dissertação (Mestrado Profissionalizante em Lasers em Odontologia)
IPEN/D-MPLO
Instituto de Pesquisas Energéticas e Nucleares - IPEN/CNEN-SP; Faculdade de Odontologia, Universidade de São Paulo, São Paulo

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NOGUEIRA, ALESSANDRO F. "Texturização em superfícies de titânio grau 2 irradiadas com laser de pulsos ultracurtos." reponame:Repositório Institucional do IPEN, 2015. http://repositorio.ipen.br:8080/xmlui/handle/123456789/23740.

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Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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LIMA, IARA B. de. "Medidas do primeiro coeficiente townsend de ionização em gases inibidores de descargas." reponame:Repositório Institucional do IPEN, 2014. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10626.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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31

AGUIAR, AMANDA A. "Avaliação do recobrimento biomimético em compósitos de alumina-zircônia texturizadas superficialmente com laser de femtossegundo." reponame:Repositório Institucional do IPEN, 2013. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10203.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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ROSSI, WAGNER de. "Construcao e operacao de lasers de neodimio: estudo do comportamento temporal." reponame:Repositório Institucional do IPEN, 1995. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10435.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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33

De, Clercq Ludwig Erasmus. "Numerical modelling of the excitation of polyatomic molecules by femtosecond laser beams." Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6522.

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Thesis (MSc)--University of Stellenbosch, 2011.
ENGLISH ABSTRACT: The selective excitation of an arbitrary vibrational level of a polyatomic molecule, without passage through an intermediary electronic excited state is demonstrated. This was achieved by simulating the interaction of a shaped, femtosecond pulse with one vibrational mode of the molecule. The carrier frequency of the pulse is chosen near resonant to the ground-to- rst-excited vibrational transition of the mode, and the pulse shape is optimized via closed-loop feedback. The simulation concentrates on the rst few vibrationally excited states since the density of states is still low, thus ensuring that the inter-vibrational decoherence time is relatively long compared to the pulse length. While various molecules were investigated this study focuses onUF6 for which detailed spectroscopic data for the v3 vibrational mode is available in literature. A multilevel model was developed and can be adapted for any number of levels. The model reported here was limited to a vibrational quantum number of four. The spectroscopic data included anharmonic splitting as well as forbidden transitions. The effect of rotational levels was not included. A density matrix approach was followed because this will allow for the introduction of dephasing of the coherent excitation via thermalizing collisions with the reservoir, as well as inter-vibrational relaxation. The time evolution of the density matrix is given by the Von Neumann equations.
AFRIKAANSE OPSOMMING: Die selektiewe opwekking van 'n arbitrêre vibrasionele vlak van 'n poliatomies molekule sonder oorgang na 'n intermediëre elektroniese opgewekte toetstand word gedemonstreer. Dit was bereik deur die interaksie te simuleer van 'n gevormde, femtosekonde pulse met een vibrasionele mode van 'n molekule. Die draer frekwensie van die pulse is so gekies dat dit naby resonansie van die grond-tot-eerste-opgewekte vibrasionele oorgang van die mode is, die puls vorm word geoptimeer deur 'n geslote-lus terugvoer. Die simulasie konsentreer op die eerste paar vibrasionele opgewekte toestande, omdat die digtheid van toestande nog steeds laag is, dus verseker dit dat inter-vibrasionele de-koherensie tyd relatief lank is in vergelyking met die puls se lengte. Verskillende molekules was ondersoek vir die studie. Die fokus is op UF6 waarvoor gedetaileerde spektroskopiese data vir die v3 vibrasionele beskikbaar is in die literatuur. 'n Multivlak model was ontwikkel en kan aangepas word vir enige aantal van vlakke. Die model wat hier aangemeld is, is beperk tot die vibrasionele kwantum getal van vier. Die spektroskopiese data het anharmonies splitting so wel as nie toegelaatbare oorgange bevat. Die effek van rotasionele vlakke was nie in berekening geneem nie. 'n Digtheids matriks benadering was gevolg, omdat dit toelaat vir die dekoherensie. Die tyd evolusie van die digtheids matriks word gegee deur die Von Neumann vergelykings.

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Mbaye, Nogaye. "Contribution à l’étude de la fiabilité des technologies avancées en environnement radiatif atmosphérique et spatial par des méthodes optiques." Thesis, Bordeaux 1, 2013. http://www.theses.fr/2013BOR15009/document.

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Ce travail présente la mise en œuvre du test par faisceau laser TPA pour l’étude de la sensibilité au phénomène SEB dans les diodes schottky en carbure de silicium. Le contexte de l’étude est décrit par un état de l’art du SEB sur les MOSFETs et Diodes en Silicium et en carbure de silicium. Une étude technologique et structurelle des composants en SiC a permis de dégager les avantages du SiC par rapport au Si conventionnel et a permis d’analyser les dégâts causés par le faisceau TPA. L’utilisation du montage expérimental sur la plateforme ATLAS dédié spécifiquement au test de matériaux à grand gap a permis de mettre en place une méthodologie de test sur des diodes schottky en SiC. L’efficacité de cette méthodologie est prouvée par l’obtention de résultats expérimentaux très originaux. La susceptibilité au SEB induit par la technique laser TPA a été démontrée. Les mesures SOA ont permis d’évaluer la robustesse des diodes schottky SiC face aux événements singuliers. Une modélisation analytique a été menée afin de comprendre la cause du mécanisme du SEB et la localisation des défauts induits par le faisceau TPA
This work presents the implementation of the TPA laser beam testing to study the SEB phenomenon in silicon carbide Schottky diodes. The context of the study is described by a state of the art of SEB on Si and SiC MOSFETs and Diodes. Technological and structural study of SiC components has identified the benefits of SiC compared to conventional Si and permits to analyze the damage caused by the TPA beam. Using the experimental setup of the ATLAS platform dedicated specifically to test large gap materials has set up a test methodology on SiC Schottky diodes. The effectiveness of this methodology is demonstrated by obtaining original experimental results. Susceptibility to SEB induced by TPA laser technique has been demonstrated. SOA measurements were used to assess the robustness of SiC Schottky diodes to single event effects.An analytical modeling was conducted to understand the cause of the SEB mechanism and the location of defects induced by the TPA beam

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Mauguet, Maxime. "Etude de la génération d'événements singuliers par excitation laser impulsionnel dans des composants silicium utilisés en environnement radiatif." Thesis, Toulouse, INSA, 2019. http://www.theses.fr/2019ISAT0012/document.

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Les composants électroniques utilisés pour des applications spatiales sont soumis à des rayonnements susceptibles de les rendre inopérants. Pour se prémunir de tels effets, leur sensibilité est testée au sol dans des accélérateurs de particules, onéreux et complexes à mettre en œuvre. Ce travail de thèse porte sur l’utilisation d’impulsions laser pour reproduire sous certaines conditions les effets des ions lourds. Le déclenchement de phénomènes parfois destructifs sur plusieurs types de composants de niveaux d’intégration différents a été obtenu sur le banc laser développé pendant cette thèse. Cela ouvre la voix à l’utilisation du laser comme outil de diagnostic en tirant partie de ses avantages en termes d’accessibilité, de coûts et de compréhension fine des effets
Electronic components used for space applications may exhibit failures under radiation. To prevent uch effects, the radiation sensitivity is evaluated using particle accelerators. Since those facilities are nly few around the world and expensive, complementary tests are needed to analyse radiation ensitivity. This work contributes to the use of laser pulses to reproduce under given conditions the ffects of heavy ions. Using the laser set-up developed during this thesis, single events which may be estructive were triggered on several types of electronic components. This paves the way to the use of aser as a diagnostic tool, given its advantages in terms of accessibility, costs and detailed analysis

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Jönsson, Olof. "Ultrafast Structural and Electron Dynamics in Soft Matter Exposed to Intense X-ray Pulses." Doctoral thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-331936.

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Investigations of soft matter using ultrashort high intensity pulses have been made possible through the advent of X-ray free-electrons lasers. The last decade has seen the development of a new type of protein crystallography where femtosecond dynamics can be studied, and single particle imaging with atomic resolution is on the horizon. The pulses are so intense that any sample quickly turns into a plasma. This thesis studies the ultrafast transition from soft matter to warm dense matter, and the implications for structural determination of proteins. We use non-thermal plasma simulations to predict ultrafast structural and electron dynamics. Changes in atomic form factors due to the electronic state, and displacement as a function of temperature, are used to predict Bragg signal intensity in protein nanocrystals. The damage processes started by the pulse will gate the diffracted signal within the pulse duration, suggesting that long pulses are useful to study protein structure. This illustrates diffraction-before-destruction in crystallography. The effect from a varying temporal photon distribution within a pulse is also investigated. A well-defined initial front determines the quality of the diffracted signal. At lower intensities, the temporal shape of the X-ray pulse will affect the overall signal strength; at high intensities the signal level will be strongly dependent on the resolution. Water is routinely used to deliver biological samples into the X-ray beam. Structural dynamics in water exposed to intense X-rays were investigated with simulations and experiments. Using pulses of different duration, we found that non-thermal heating will affect the water structure on a time scale longer than 25 fs but shorter than 75 fs. Modeling suggests that a loss of long-range coordination of the solvation shells accounts for the observed decrease in scattering signal. The feasibility of using X-ray emission from plasma as an indicator for hits in serial diffraction experiments is studied. Specific line emission from sulfur at high X-ray energies is suitable for distinguishing spectral features from proteins, compared to emission from delivery liquids. We find that plasma emission continues long after the femtosecond pulse has ended, suggesting that spectrum-during-destruction could reveal information complementary to diffraction.

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OLIVEIRA, EDUARDO S. "Ablação seletiva de um filme de nitreto de titânio em substrato de carboneto de tungstênio utilizando laser de pulsos ultracurtos." reponame:Repositório Institucional do IPEN, 2017. http://repositorio.ipen.br:8080/xmlui/handle/123456789/27976.

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Revestimentos superficiais são aplicados à muitas ferramentas de usinagem na indústria metalúrgica com o intuito de melhorar a eficiência de corte e aumentar sua vida útil. Neste trabalho foram realizados testes para remoção do recobrimento de nitreto de titânio alumínio (TiAlN) em pastilhas de carboneto de tungstênio (WC-Co), utilizando um feixe laser de pulsos ultracurtos. Após a determinação dos limiares de dano do filme e do substrato foram ablacionados na superfície do recobrimento, traços utilizando duas condições de ablação. Inicialmente operou-se no regime de baixa fluência do filme, e posteriormente no regime de baixa fluência do substrato, muito abaixo do limiar do filme, aplicando-se alta sobreposição de pulsos. Um sistema de espectroscopia de emissão atômica induzida por laser (LIBS) foi montado para monitoramento dos materiais presentes no plasma gerado pelo laser, porém o sistema não apresentou sensibilidade suficiente para leitura da baixa intensidade do plasma proveniente do processo e não foi utilizado. Após a análise dos traços por microscopia eletrônica, perfilometria óptica e espectroscopia por fluorescência de Raios-X, não foi possível determinar um processo seguro para realizar a remoção seletiva do filme em questão, porém, devido aos dados obtidos e observações dos resultados em alguns traços, novas possibilidades foram levantadas, abrindo a discussão para a realização de trabalhos futuros.
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

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38

Mutin, Pascal. "Génération de fréquences infrarouges par mélange de lasers à colorants pulsés dans des cristaux non linéaires : application à la spectroscopie à haute résolution." Dijon, 1988. http://www.theses.fr/1988DIJOS023.

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Deux radiations de grandes finesses spectrales (6 mhz) provenant de deux lasers à colorant impulsionnels (puissances crêtes 7kw et 12 kw), ceux-ci amplifiant une longueur d'onde continue, sont mélangées dans le cristal de iodate de lithium. La fréquence générée par ce milieu est la différence de leurs fréquences et est accordable dans l'infrarouge de 1600 cm-1 à 2600 cm-1. Une première étude porte sur les caractéristiques de la source infrarouge. Du fait de la finesse spectrale de cette source (environ 6mhz),un spectromètre infrarouge haute résolution fonctionnant sur le principe de l'absorption différentielle a été conçu. Une deuxième étude rend compte des performances d'un tel spectromètre : celles-ci ont été testées sur la molécule de protoxyde d'azote.

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Gibson, D. J. "A High-Energy, Ultrashort-Pulse X-Ray System for the Dynamic Study of Heavy, Dense Materials." Washington, D.C : Oak Ridge, Tenn. : United States. Dept. of Energy ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2004. http://www.osti.gov/servlets/purl/15011626-GeBNVt/native/.

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Thesis (Ph.D.); Submitted to Univ. of California, Davis, CA (US); 17 Sep 2004.
Published through the Information Bridge: DOE Scientific and Technical Information. "UCRL-TH-207378" Gibson, D J. 09/17/2004. Report is also available in paper and microfiche from NTIS.

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Roche, Nicolas J.-H. "Caractérisation et modélisation de l'influence des effets cumulés de l'environnement spatial sur le niveau de vulnérabilité de systèmes spatiaux soumis aux effets transitoires naturels ou issus d'une explosion nucléaire." Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20108.

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L'environnement radiatif spatial est composé d'une grande diversité de particules dans un spectre en énergie très large. Parmi les effets affectant les composants électroniques, on distingue les effets cumulatifs et les effets singuliers transitoires analogiques (ASET). Les effets cumulatifs correspondent à une dégradation continue des paramètres électriques du composant induits par un dépôt d'énergie à faible débit de dose tout au long de la mission spatiale. Les ASETs sont eux causés par le passage d'une particule unique traversant une zone sensible du composant et engendrant une impulsion de tension transitoire qui se propage à la sortie de l'application. Au cours des tests au sol, les deux effets sont étudiés séparément, mais ils se produisent simultanément en vol. Il se produit donc un effet de synergie, induit par la combinaison de la dose et de l'apparition soudaine d'un ASET dans le dispositif préalablement irradié.Une étude de l'effet de synergie dose-ASET est proposée. Pour accélérer les irradiations, une technique connue sous le nom de « méthode de commutation de débit de dose » (DRS) prenant en compte la sensibilité accrue au faible débit de dose (ELDRS) est utilisée. Un modèle haut niveau est développé en utilisant l'analyse circuit permettant de prédire l'effet de synergie observé sur un amplificateur opérationnel à trois étages. Pour prédire l'effet de synergie, l'effet de dose est pris en compte en faisant varier les paramètres décrivant le modèle suivant une loi de variation déduite de la dégradation du courant d'alimentation qui est couramment enregistré au cours des essais industriels. Enfin, les effets transitoires des radiations sur l'électronique (TREEs) induits par un environnement de très fort débit de dose de rayons X pulsés ainsi que l'effet de synergie dose-TREE sont étudiés à l'aide d'un générateur de Flash-X. La méthode classique d'analyse des ASETs permet alors d'expliquer la forme des impulsions transitoires observées
The natural radiative space environment is composed by numerously particles in a very large energy spectrum. From an electronics component point of view, it is possible to distinguish cumulative effects and so-called Analog Single Event Transient effects (ASET). Cumulative effects correspond to continuous deterioration of the electrical parameters of the component, due to a low dose rate energy deposition (Total Ionizing Dose: TID) throughout the space mission. ASETs are caused by a single energetic particle crossing a sensitive area of the component inducing a transient voltage pulse that occurs at the output of the application. During ground testing, both effects are studied separately but happen simultaneously in flight. As a result a synergy effect, induced by the combination of the low dose rate energy deposition and the sudden occurrence of an ASET in the device previously irradiated, occurs. A study of dose-ASET synergistic effects is proposed using an accelerated irradiation test technique known as Dose Rate Switching method (DRS) tacking into account the concern of the Enhanced Low Dose Rate Sensitivity (ELDRS). A High Level Model is developed using circuit analysis to predict the synergy effect observed on a three stages operational amplifier. To predict synergy effect, the TID effect is taken into account by varying the model parameters following a variation law deduced from the degradation of the supply current which recorded during usual industrial TID testing. Finally, the Transient Radiation Effects on Electronics (TREE) phenomena induced by a Very High Dose Rate X-ray pulse environment and the dose-TREE synergy effect are then investigated using an X-ray flash facility. The classical ASETs methodology analysis can explain the shapes of transients observed

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Jacquet, Maxime J. "Negative frequency at the horizon : scattering of light at a refractive index front." Thesis, University of St Andrews, 2017. http://hdl.handle.net/10023/11780.

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This thesis considers the problem of calculating and observing the mixing of modes of positive and negative frequency in inhomogeneous, dispersive media. Scattering of vacuum modes of the electromagnetic field at a moving interface in the refractive index of a dielectric medium is discussed. Kinematics arguments are used to demonstrate that this interface may, in a regime of linear dispersion, act as the analogue of the event horizon of a black hole to modes of the field. Furthermore, a study of the dispersion of the dielectric shows that five distinct configurations of modes of the inhomogeneous medium at the interface exist as a function of frequency. Thus it is shown that the interface is simultaneously a black- and white-hole horizon-like and horizonless emitter. The role, and importance, of negative-frequency modes of the field in mode conversion at the horizon is established and yields a calculation of the spontaneous photonic flux at the interface. An algorithm to calculate the scattering of vacuum modes at the interface is introduced. Spectra of the photonic flux in the moving and laboratory frame, for all modes and all realisable increase in the refractive index at the interface are computed. As a result of the various mode configurations, the spectra are highly structured in intervals with black-hole, white-hole and no horizon. The spectra are dominated by a negative-frequency mode, which is the partner in any Hawking-type emission. An experiment in which an incoming positive-frequency wave is populated with photons is assembled to observe the transfer of energy to outgoing waves of positive and negative frequency at the horizon. The effect of mode conversion at the interface is clearly shown to be a feature of horizon physics. This is a classical version of the quantum experiment that aims at validating the mechanism of Hawking radiation.

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Pai, Shyh-Shii, та 白世璽. "Pulsed Tera-hertz Radiation from Femto-second Laser Excited Superconductive YBa2Cu3O7-δ Antenna". Thesis, 2005. http://ndltd.ncl.edu.tw/handle/72255765679973600789.

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博士
國立清華大學
物理學系
94
The physics of short-pulse terahertz radiation has recently become an active research field, with interest both in fundamental aspects of generation and detection of tera-hertz (THz) radiation and in spectroscopic applications after many pioneering researches done in the past twenty years. Many methods have been exploited to develop different sources of pulsed THz. One simple method to generate THz radiation is to create the ultrafast current transients in a semiconductor switch illuminated with femtosecond laser pulses. It is also expected that the THz radiation should be emitted from superconductors if the supercurrent is modulated at a sufficiently high speed by femtosecond laser pulses. However, the ultrafast electromagnetic properties of radiated THz pulses from superconductors are generally quite complicated and not well understood. This is particularly true when high power of THz is generated at the condition of high bias current or pumping power. In this dissertation, we observed the ultrashort electromagnetic pulse radiation from a current-biased bow-tie structure of YBa2Cu3O7-δ thin film dipole antenna on MgO substrate by using 100 fs, 750 nm laser pulses. With the scheme of electro-optic detection, we obtained the THz pulses with 1.0 ps full width at half maximum, containing frequency components up to 1.0 THz. The parallel polarization of THz radiation emitted from a current biased superconductive antenna to the direction of the bias current exhibits that the ultrashort pulses were due to a straight current flowing along the bridge, not the current loop at the luminous area of the bridge. The observed radiation waveforms emitted from a superconductor differ slightly from that radiated by a conventional semiconductor antenna. Moreover, the radiation waveforms for superconductors obtained by other researches are also dissimilar to each other. Almost all other researchers focused on the dependence of THz radiation amplitude for superconductors, they did not address the radiated pulse shape. Namely, no theories or models have been developed to describe the transient carrier dynamics in the nonequilibrium state of superconductors. In order to explain the shape of radiation waveforms emitted from the superconductor and describe the transient carrier dynamics, first we discuss the experimental results in relation to the radiation pattern, polarization, and capacitor effect to confirm the origin of ultrashort electromagnetic pulses radiated from a superconducting antenna. Then, we construct a more complete model by using the concept of carrier acceleration based on the classical electrodynamics. For a constant-current biased superconducting antenna, we propose that the total constant current density consists of time-varying suppercarriers and normal carriers in the two-fluid model when the superconducting antenna is excited by femtosecond laser pulses. The transient carrier dynamics in this nonequilibrium state can be obtained by using the Rothwarf and Taylor rate equations. We have solved successfully the time transient quasiparticles density in the nonequilibrium state of superconductors and the calculated far-field radiation fits well for the radiation waveforms with some fitting parameters, such as the recombination rate, phonon pair breaking time and the mobility of the normal carriers. Through the simulated fitting with our observed waveforms, we can estimate that the product of quasipartcle recombination rate and phonon pair breaking time for the YBCO superconductor at low temperatures is five-time larger than the metallic superconductor Pb. It implies that the YBCO superconductor presents a stronger electron-phonon interaction than the metallic superconductor. The effective mobility for normal carriers also obtained from the fitting shows the impurity dominated characteristics of the YBCO thin film and the mobility in real units is estimated to be μq = 660 (cm2 / V-s), comparable to the hole mobility of Si at room temperature. We also investigated widely the THz emission properties of YBCO antenna by measuring the pumping power, bias current and ambient temperature dependences on the radiation amplitudes. The THz peak amplitude dependence shows the saturation and a nonlinear behavior with a higher excitation pumping power and with the applied bias currents. The saturation on the dependence with the excitation powers exhibits the bolometric heating in nature. However, the measured nonlinear dependence on the applied bias current deviated from our linear simulated results on the effective current density especially at moderate and high pump powers or low temperatures. It indicates that our model should be considered more accurately describing the deviation. Finally, we discussed the possibilities to eliminate the deviation by replacing a nonlinear term in the supercarrier density for our model or taking the screen effects into account with the simulated results.

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Pettit, George H. "Pulsed ultraviolet laser ablation: Theoretical considerations and applications in medicine." Thesis, 1990. http://hdl.handle.net/1911/16381.

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Pulsed ultraviolet lasers can be used to induce clean etching in organic and some inorganic materials. This effect is called photoablation or ablative photodecomposition. Although the precise cause remains unknown, this phenomenon is becoming of vital importance in micromachining, materials processing, and medicine. To better understand the photoablation process, a theoretical description of the process has been developed. This description is based on a treatment of the radiation transport of intense ultraviolet light pulses through absorbing organic material. The theory predicts deviations from Beer's Absorption Law at high intensities which are in fact observed. These discrepancies are due to three main effects: saturation of the finite number of chromophores in the material, multiphoton absorption, and attenuation of laser light by ablation products. Using the analysis to model the ablation process it is possible to describe observed ablation behaviors for a variety of synthetic and biological substrates. Excimer laser photoablation has also been studied experimentally as a means of removing occlusive arterial thrombi. Thrombi induced in canine coronary arteries were removed with XeF excimer laser light (351 nm) delivered via flexible optical fiber. The results of this study indicated that it was possible to remove significant thrombi (27 mg mass) within 3 minutes, without causing injury to the adjacent arterial wall. In addition, the ablation products consisted of a minute volume of gas and small particulate debris ($>$100 $\mu$m), which would not be a cause of concern in a clinical procedure. Excimer laser induced autofluorescence signatures have been analyzed as possible diagnostic aids in laser angioplasty procedures. Spectra acquired from cadaver artery samples using low intensity laser light revealed distinct differences in fluorescence response between healthy and atherosclerotic arterial wall. Fluorescence spectra acquired during tissue ablation with intense laser pulses also exhibited variation between healthy and diseased sites. Spectral examination of tissue sites after ablative tissue removal showed changes in fluorescence response which coincided with penetration of diseased lesions. These findings indicated that it should be possible to use UV laser fluorescence spectroscopy to target atherosclerotic lesions and to monitor in real time the ablative removal of these vessel obstructions.

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Wang, Jin Jimmy. "Melting in Superheated Silicon Films Under Pulsed-Laser Irradiation." Thesis, 2016. https://doi.org/10.7916/D8NV9J7Q.

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This thesis examines melting in superheated silicon ﬁlms in contact with SiO₂ under pulsed laser irradiation. An excimer-laser pulse was employed to induce heating of the ﬁlm by irradiating the ﬁlm through the transparent fused-quartz substrate such that most of the beam energy was deposited near the bottom Si-SiO₂ interface. Melting dynamics were probed via in situ transient reﬂectance measurements. The temperature proﬁle was estimated computationally by incorporating temperature- and phase-dependent physical parameters and the time-dependent intensity proﬁle of the incident excimer-laser beam obtained from the experiments. The results indicate that a signiﬁcant degree of superheating occurred in the subsurface region of the ﬁlm. Surface-initiated melting was observed in spite of the internal heating scheme, which resulted in the ﬁlm being substantially hotter at and near the bottom Si-SiO₂ interface. By considering that the surface melts at the equilibrium melting point, the solid-phase-only heat-ﬂow analysis estimates that the bottom Si-SiO₂ interface can be superheated by at least 220K during excimer-laser irradiation. It was found that at higher laser ﬂuences (i.e., at higher temperatures), melting can be triggered internally. At heating rates of 10¹⁰ K/s, melting was observed to initiate at or near the (100)-oriented Si-SiO₂ interface at temperatures estimated to be over 300K above the equilibrium melting point. Based on theoretical considerations, it was deduced that melting in the superheated solid initiated via a nucleation and growth process. Nucleation rates were estimated from the experimental data using Johnson-Mehl-Avrami-Kolmogorov (JMAK) analysis. Interpretation of the results using classical nucleation theory suggests that nucleation of the liquid phase occurred via the heterogeneous mechanism along the Si-SiO₂ interface.

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45

Chang, Ju-Chung, and 張譽鐘. "THz Radiation from Semiconductors under Magnetic Field Irradiated with Femtosecond Laser Pulses." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/25829788837693140159.

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碩士
國立清華大學
電子工程研究所
88
Since a rigorous theory for THz radiation generated in magnetic field has not yet been constructed, we want to investigate some properties of the radiation to understand the generating mechanism. We first setup the THz emitter sources in our electro-optic (EO) and antenna detection systems respectively and then do some analyses on the waveforms obtained from these systems to prepare for our further researches. We compared the difference between radiations by electric field mechanism and by magnetic field mechanism and find the bandwidth of THz radiation from InAs in magnetic field is wider than that from SI-GaAs in electric filed. In the magnetic field case, the radiation spectrum is influenced not only by magnetic field intensity but also by the collecting position. We also find the quadratic relationship of radiation power dependence on magnetic field intensity as reported by X.-C. Zhang et al. and N. Sarukura et al. As the magnetic intensity growing larger and larger, the radiation distribution is found to be more and more uniform. Beside, the spatial beam profile is measured to be a Gaussian as in the electric case. Furthermore, we have also test several different samples, and this is very helpful for us to understand the underlying physics in this mechanism.

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