Дисертації з теми "Radiation shaping"
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-19 дисертацій для дослідження на тему "Radiation shaping".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте дисертації для різних дисциплін та оформлюйте правильно вашу бібліографію.
Čelanović, Ivan. "Thermophotovoltaics : shaping the flow of thermal radiation." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37918.
Повний текст джерелаIncludes bibliographical references (p. 121-123).
This thesis explores the modeling, design, and optimization of photonic crystals as spectral control components for high-performance thermophotovoltaic (TPV) power conversion. In particular, we focus on the use of one-dimensional and two dimensional photonic crystals as optical filters and selective thermal emitters for thermophotovoltaic and micro-thermophotovoltaic (micro-TPV)) applications. In addition, we explore fundamental limitations of photonic crystal thermal emitters and provide new insights into the limiting power transfer mechanisms that are relevant for TPV, micro-TPV, lighting and sensor applications. Ideal thermodynamic models that capture dominant power transfer mechanism for TPV and micro-TPV case, are developed and used for the design, optimization and system performance estimation of TPV systems with photonic-crystals. Furthermore, we propose for the first time two new classes of narrow-band thermal emitters that use the resonant cavity effect. The first type of narrow-band thermal emitters rely on vertical-cavity to enhance the thermal emission of highly reflective materials (e.g metals). This class of emitters was named the vertical cavity enhanced resonant thermal emitter (VERTE).
(cont.) The second type of resonant thermal emitters rely on guided resonances in a two-dimensional photonic crystal slab to enhance the emittance of a high-dielectric low-absorption material (e.g. silicon). Both types of resonant thermal emission sources are quasi-monochromatic, and partially-coherent thermal sources that hold great promise for applications ranging from highly-efficient TPV systems to near-IR and IR sensors. Finally, experimentally measured spectral characteristics of fabricated one-dimensional and two-dimensional photonic-crystals show excellent correlation with simulation results. It was shown that a TPV system comprising of the proposed front-side filter and selective thermal emitter exhibits a three-fold enhancement in efficiency over the conventional TPV systems.
by Ivan Čelanović.
Sc.D.
Van, der Walt Jacobus Gert. "Radiation field shaping through low temperature thermal-spray in radiotheraphy." Thesis, Bloemfontein : Central University of Technology, Free State, 2009. http://hdl.handle.net/11462/116.
Повний текст джерелаSuperficial cancerous lesions are commonly treated through low energy X-ray or electron radiation in radiotherapy. The treatment units that produce the radiation are equipped with square, rectangular and round applicators of different sizes. These applicators attach to the treatment units and define the radiation field size applied during treatment. An applicator is chosen to fit the shape of the cancerous lesion on the patient as closely as possible. Since cancerous lesions are irregular in shape, there will always be an area of healthy tissue between the edge of the lesion and the edge of the standard field shape. This healthy tissue will be irradiated along with the lesion during treatment which is undesirable since the cancer wound heals through reparative growth of the surrounding healthy tissue after treatment. Traditional techniques that were developed to shield this healthy tissue and thus shape the radiation field to the shape of the lesion present various shortcomings. This study introduces a new thermal-spray process for producing radiation field shaping shields which overcomes most of the shortcomings encountered with the traditional field shaping techniques. Since none of the commercially available thermal-spray equipment could be used to produce field shaping shields, new thermal-spray equipment was designed and fabricated tailor made to the application. Different techniques to determine the contours of the treatment area on the patient were investigated. These included a patient contact technique using a plaster bandage impression and a non-contact technique using 3D laser scanning. From the plaster bandage impression a plaster model can be produced onto which a high density low melt material such as Wood’ s alloy can be thermally sprayed to produce a field shaping mask. A model can also be produced from the 3D laser scanning data through laser sintering (LS) in nylon polyamide powder or through computer numerical controlled (CNC) milling in a block of low density polyurethane. The thermal-spray technique was evaluated by comparing the field shaping ability of radiation shields produced through the technique to the field shaping ability of shields produced through the traditional techniques. Radiographic film was used for this purpose and the results are presented in the form of isodensity charts. The required thicknesses of thermal-sprayed field shaping masks to shield radiation of various energies were also determined. The thicknesses were determined through radiation transmission measurements of known thicknesses of sprayed sheets of Wood’ s alloy. X-ray imaging showed that there were no defects present within thermal-sprayed layers of Wood’ s alloy that may negatively affect the shielding ability of masks produced through the technique.
Scott, H. M. "Near field modification techniques for pattern shaping in antenna elements and arrays." Thesis, Queen's University Belfast, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269176.
Повний текст джерелаWanis, Sameh Sadarous. "Tailored Force Fields for Flexible Fabrication." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10540.
Повний текст джерелаDu, Plessis Anton. "A characterization of beam shaping devices and a tunable Raman laser." Thesis, Stellenbosch : University of Stellenbosch, 2003. http://hdl.handle.net/10019.1/16313.
Повний текст джерелаENGLISH ABSTRACT: The efficient manipulation of various nonlinear optical processes frequently requires the shaping of the laser beams used for these processes. Three beam shaping techniques were investigated in this thesis. The focussing of Gaussian laser beams was investigated analytically, in order to efficiently manipulate the focussed beam characteristics. The beam-shaping characteristics of a diffractive optical element (DOE) was investigated numerically, which illustrates the beamshaping capability of the DOE, and identifies the critical parameters in experimental situations. The use of a waveguide as beam shaping device was investigated analytically and experimentally, and characterized for use with the available tunable laser sources. A Raman laser, or Raman shifter, employs stimulated vibrational Raman scattering to generate laser radiation at shifted frequencies. The waveguide was successfully applied as a beam shaping device in the Raman laser system, for optimisation of the process. The Raman laser system was investigated experimentally and characterized for use with the available tunable laser sources. The successful generation of laser radiation at shifted frequencies illustrates the usefulness of the system for generating tunable red-shifted frequencies. The results of this work allow the simple and efficient application of the Raman laser to generate laser radiation at shifted frequencies, in particular tunable infrared laser radiation which is desirable for molecular spectroscopy.
AFRIKAANSE OPSOMMING: Nie-liniêre optiese prosesse kan meer effektief benut word deur die vervorming van die laserbundels wat gebruik word in die prosesse. In hierdie tesis word drie laserbundel-vervormings tegnieke ondersoek. Die fokussering van Gaussiese laserbundels word analities ondersoek, om die gefokusseerde bundel se eienskappe effektief te manipuleer. Die bundel-vervormings eienskappe van ’n diffraktiewe optiese element word numeries ondersoek, wat die effektiwiteit van die bundelvervorming en die sensitiewe parameters in die sisteem uitwys. Die gebruik van ’n golfgeleier as ’n bundel-vervormings tegniek word ook analities en eksperimenteel ondersoek, en gekarakteriseer vir gebruik met die gegewe golflengte-verstelbare laser sisteme. ’n Raman laser, wat gestimuleerde vibrasionele Raman verstrooiing gebruik om laser lig te genereer by Stokes-verskuifde frekwensies, word ondersoek. Die golfgeleier word effektief gebruik as ’n bundel-vervormings tegniek in die Raman laser, om die bogenoemde nie-liniêre proses te optimeer. Die Raman laser was eksperimenteel ondersoek en gekarakteriseer vir gebruik met die gegewe golflengte-verstelbare lasers. Laser lig by verskuifde golflengtes is suksesvol gegenereer, wat die bruikbaarheid van die sisteem illustreer. Van belang is spesifiek verstelbare infrarooi laser lig, wat gebruik kan word in die laser-spektroskopie van molekules. Die resultate van hierdie werk lei tot die eenvoudige en effektiewe gebruik van die Raman laser, om langer golflengtes in die infrarooi gebied te genereer met ’n gegewe laser in die sigbare gebied.
Cavallone, Marco. "Application of laser-plasma accelerated beams to high dose-rate radiation biology." Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX063.
Повний текст джерелаCancer is the second leading cause of death globally, accounting for an estimated 9.6 million deaths, or one in six deaths, in 2018. Besides surgery and chemotherapy, radiotherapy is one of the major treatment modality. It consists in the use of ionising radiation to kill cancerous cells by depositing energy into the tumour and destroying the genetic material that controls how cells grow and divide. While both cancerous and healthy cells are damaged by radiation, the goal of radiotherapy is to increase the treatment selectivity by sparing as much as possible the healthy tissues. Optimisation of the selectivity reposes on several aspects, including spatial optimisation of the dose, precision of imaging techniques and dosimetry instruments, use of different radiations and temporal structures of dose delivery. In particular, the role of the dose-rate and the total irradiation time has not been extensively explored yet.Clinical accelerators typically deliver the dose with a dose rate around few Gy/min, leading to exposure times in the order of few minutes to deliver a therapeutic dose. While the effect of a reduction of the dose rate in the order of cGy/min is well known, the effect of high-dose rate, fast irradiation on living cells still need to be elucidated. Evidences of an effect of the high dose-rate on the biological response have been recently observed in many studies. In particular, in-vivo studies performed with electrons and photons produced by accelerator prototypes have shown that delivering the prescribed dose in a short exposure time (<500ms) and at a high dose-rate (>40Gy/s) increases the treatment selectivity by reducing the occurrence of secondary effects on healthy tissues compared to conventional treatments with the same total dose. Although theoretical explanations underpinning such phenomenon are still under discussion, the so-called FLASH protocol has been successfully tested with the first human patient in 2019, paving the way for further research in this domain. These important results point out the importance of the dose delivery modality on the treatment selectivity and the potential benefit that high dose-rate protocols may bring to clinics, asking for a deeper understanding of the physico-chemical and biological processes following fast dose deposition.In this scenario, Laser-Driven Particle (LDP) beams represent a unique tool to shed some light on the radiobiological response following high-dose rate irradiation. LDP sources are produced by focusing an ultra-short (~fs) and ultra-intense (1019 W/cm2) laser pulse on a solid or gaseous thin target (~μm), producing proton and electron bunches with duration of respectively a few picoseconds and a few femtoseconds. These characteristics allow the reach of extremely high peak dose-rate in the pulse of the order of ~109 Gy/s in comparison with conventional and FLASH treatment protocols. For this reason, LDP sources have been receiving great attention in the last decade, but their radiobiological effect is still debated and further systematic studies are required.This thesis discusses the potential of both Laser-Accelerated Protons (LAP) and Laser-Accelerated Electrons (LAE) produced by different types of commercially available high-power lasers systems. In particular, it presents experimental and theoretical studies carried out with three different types of LDP beams, i.e. Hz LAPs, single-shot LAPs and kHz LAEs, enabling different temporal modalities of dose delivery. The goal is to address some of the main issues related to the application of such sources to radiation biology and show viable solutions and irradiation protocols to perform systematic radiobiology studies. Such issues include accurate characterisation of the source, optimisation of the dose distribution at the biological target through the design of adapted transport beamlines and investigation of the behaviour of dosimetric instruments for high dose-rate dosimetry
Kropáč, Ondřej. "Návrh tvarovacího systému pro laserový svazek." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2011. http://www.nusl.cz/ntk/nusl-219163.
Повний текст джерелаDe, 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.
Повний текст джерелаENGLISH 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.
Baretela, Michael J. "Increasing prompt response from impulse radiating antenna by aperture shaping." Thesis, Monterey California. Naval Postgraduate School, 2002. http://hdl.handle.net/10945/6094.
Повний текст джерелаIn order to improve the prompt response from an impulse radiating antenna (IRA)number of studies have suggested controlling the spatial distribution of the aperture fields by changing the feed arm angle. Other work has suggested that proper shaping of the aperture can further enhance the radiated signal for a given feed structure. This paper shows how the radiated prompt response can be maximized for a given feed arm configuration by shaping the aperture to eliminate fields orientated in the wrong direction. The percent increase in the prompt radiated electric field for a 200 . IRA with a ideally shaped aperture compared to a standard circular aperture ranged from 0.42% to 39.94% depending on the input electrode angle. For the most common electrode angles of 45Ê» and 60Ê» the increases are 6.00% and 16.63% respectively.
Gagnon, Nicolas. "Phase Shifting Surface (PSS) and Phase and Amplitude Shifting Surface (PASS) for Microwave Applications." Thesis, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/19826.
Повний текст джерелаFredenberg, Erik. "Spectral Mammography with X-Ray Optics and a Photon-Counting Detector." Doctoral thesis, KTH, Medicinsk avbildning, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11641.
Повний текст джерелаQC 20100714
Iliopoulos, Ioannis. "Engineering the near field of radiating systems at millimeter waves : from theory to applications." Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1S165.
Повний текст джерелаWith the demand for near-field antennas continuously growing, the antenna engineer is charged with the development of new concepts and design procedures for this regime. From the microwave and up to terahertz frequencies, a vast number of applications, especially in the biomedical domain, are in need for focused or shaped fields in the antenna proximity. This work proposes new theoretical methods for near-field shaping based on different optimization schemes. Continuous radiating planar apertures are optimized to radiate a near field with required characteristics. In particular, a versatile optimization technique based on the alternating projection scheme is proposed. It is demonstrated that, based on this scheme, it is feasible to achieve 3-D control of focal spots generated by planar apertures. Additionally, with the same setup, also the vectorial problem (shaping the norm of the field) is addressed. Convex optimization is additionally introduced for near-field shaping of continuous aperture sources. The capabilities of this scheme are demonstrated in the context of different shaping scenarios. Additionally, the discussion is extended to shaping the field in lossy stratified media, based on a spectral Green's functions approach. Besides, the biomedical applications of wireless power transfer to implants and breast cancer imaging are addressed. For the latter, an extensive study is included here, which delivers an outstanding improvement on the penetration depth at higher frequencies. The thesis is completed by several prototypes used for validation. Four different antennas have been designed, based either on the radial line slot array topology or on metasurfaces. The prototypes have been manufactured and measured, validating the overall approach of the thesis
Stein, Kenneth Merritt. "Effects of pulse shaping on Cerenkov radiation." Thesis, 1986. http://hdl.handle.net/10945/21816.
Повний текст джерелаChuang, Cing-Jung, and 莊沁融. "Femtosecond Pulse Shaping Methodology and its Applications in Tera-Hertz radiation enhancement." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/95896564345819969232.
Повний текст джерела國立交通大學
光電工程系所
93
Fourier-transform (FT) optical shaping is now a useful technology for generating nearly arbitrarily shaped ultrafast optical pulses, with applications ranging from coherent control to high-speed communications. We constructed a pulse shaping system,and modulated light to generate THz. Using pulse shaping technique could enhance THz radiation, and the enhancement was Over 40%. It was demonstrated by positive chirped optical pulses. This could be attributed to the band filling process.
Huang, Shiuan-Hua, and 黃玄驊. "Development of Novel Pulse Shaping Technique and Its Application for Terahertz Radiation." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/50132768032799721667.
Повний текст джерела國立中山大學
光電工程學系研究所
100
In this thesis, a novel method for multi-pulse with equal chirp characteristics and more efficient THz generation through two photon absorption (TPA) are investigated and demonstrated. These are all the first time, for our best knowledge, odd multi-pulses generation and innovative approach for efficient THz through TPA are proposed and studied. By modulating the amplitude and phase of the spatial light modulator with the pulse shaper, the number of multi-pulses can be adjustable without the limitation of even number only. Meanwhile, the chirp properties of the generated pulses are with the same characteristics and tunable also. For the case with bandwidth of 10nm, the generated multi-pulses with equal chirps varying from -20000fs^2 to 20000fs^2 are demonstrated and the results have a good agreement with the theoretical estimation. We also discuss the number of the multi-pulses and inequalities of the amplitude of the pulses are limited by the spectral resolution of SLM within the pulse shaper. Regarding to efficient THz radiation, it can be generated more efficiently from a low-temperature-grown GaAs (LT-GaAs) photoconductive (PC) antenna by taking into account the TPA induced photo-carrier in the photoconductor. A rate-equation-based approach using the Drude-Lorentz model taking into account the band-diagram of LT-GaAs is used for the theoretical analysis. The super-linear power dependent photocurrent clarifies the role of TPA. Previously unnoticed THz pulse features and anomalously increasing THz radiation power rather than saturation were observed. These are in good agreement with the theoretical predictions.
Lin, Sung-Hui, and 林松輝. "The Study of Terahertz Radiation Mechanism from Photoconductive Antenna by Femtosecond Pulse Shaping Technology." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/24774906421031645008.
Повний текст джерела國立交通大學
光電工程系所
96
In this thesis, role of chirp properties within mode locked pulses to generate efficiency and broadband THz radiation is investigated. By integration of pulse shaping technique and pump-probe measurement, behavior of increasing carrier relaxation time with chirp and positive sign is observed and explained by frequency dependent excess energy. Meanwhile, chirp- and power- dependence of THz radiation are studied using chirp controlled PC antenna based THz radiation system. We confirm the nature of asymmetry and positive preference of THz radiation for mode locked chirp pulse. We further observe an anomalous and nonlinear increase of THz radiation with increasing power of transform-limited and tight focusing exciting pulse. This could be due to distribution of carries from two photon absorption and is the first experimental report of two photon absorption induced THz radiation enhancement which have been predicted theoretically. In addition, we analyze phenomenon observed by Drude-Lorentz model with obtained chirp- and power- dependent carrier lifetime and influence of chirp within sampling. Finally, we suggest possible approaches for generating high efficiency and broadband THz radiation:(1) positive chirp exciting can enhance radiation power but depress the high frequency part. (2) transform-limited exciting pulse can provide broader spectrum and further enhance power under highly tight focusing condition due to TPA contribution. (3) antenna with short carrier and momentum lifetime exciting by transform-limited pulse to decrease influence of PC sampling.
Alvarez, Ojeda Agustín. "Estudio del diseño y desarrollo de un prototipo de generador de rayos X convergentes para aplicaciones en radioterapia externa." Bachelor's thesis, 2017. http://hdl.handle.net/11086/6555.
Повний текст джерелаEl objetivo principal de este trabajo fue la obtención, por medio de un prototipo, de un haz de rayos X convergente capaz de generar una alta concentración de dosis en una pequeña región dentro de un medio blanco. Se propuso un ánodo original (sin respaldo de estudios previos), dado por una configuración cobre-plomo-cobre y se realizó un estudio detallado del mismo. En una pequeña región (menor a 2cm × 2cm × 2cm) dentro del blanco irradiado (cubo de agua de 30cm de lado) se logró una concentración de dosis alta (más de 10 veces la dosis que en cualquier otra región del blanco), observándose que el tamaño de dicha región depende fuertemente de la colimación del haz y la geometrı́a global del ánodo. Se comprobó también que los filtros y las proporciones entre los materiales del ánodo definen el número y espectro de fotones y electrones en el haz incidente, y por tanto, la penetración y concentración de la dosis.
Harper, Brent M. "Iterative, diffraction-based synthesis technique for dual-mirror beam shaping and invesigations of radiation patterns from corrugated, circular waveguides." 1995. http://catalog.hathitrust.org/api/volumes/oclc/34068376.html.
Повний текст джерелаTypescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 79).
Dias, Diogo Telmo Cruz. "Transimpedance amplifier for early detection of breast cancer." Master's thesis, 2014. http://hdl.handle.net/10362/13336.
Повний текст джерела