Generation of Sub-picosecond Terahertz Radiation by Laser-produced Plasmas PDF Download
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Author: Harald Hamster
Publisher:
ISBN:
Category :
Languages : en
Pages : 340
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Author: Harald Hamster
Publisher:
ISBN:
Category :
Languages : en
Pages : 340
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Author: Margaret Murnane
Publisher:
ISBN:
Category : Picosecond pulses
Languages : en
Pages : 324
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Author: Amrutha Gopal
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Terahertz waves are the last part of the electro magnetic spectrum to be measured and therefore relatively less explored compared to other spectral bands. They are considered to be harmless to living beings on exposure thanks to their low photon energy and possess many unique properties such as quasi static (~ps) electric and magnetic fields, which can observe, excite and control multitude of physical phenomena like solvation of water molecules in biological systems, non-equilibrium dynamics in unconventional superconductors, ferrites, semiconductors, magnetic materials and investigation of protein folding dynamics etc. thus making them the light wave of the future. Intense THz pulses with MV/cm fields are required for nonlinear vibrational spectroscopy, generation of high energy photons (XUV radiation) and for studying higher order nonlinear effects.There are various established techniques to generate high-power THz pulses. Laser-plasma based sources are a promising alternative to the established schemes due to their compactness and scalability. The work presented here investigates the generation of high-power, broadband terahertz radiation from thin foil targets at incident laser intensities above I > 10^18 W/cm^2. THz radiation from the foil rear surface has been proposed for the first time and showed that the radiation itself can be employed as a novel diagnostic to understand the charged particle dynamics. A detailed experimental investigation on the terahertz generation with respect to the incident laser and target parameters and its characterization are presented. Numerical calculations based on the charge particle detected from the rear surface was carried out and the results were compared with the experimental observations. The analysis points out that three main processes give rise to coherent THz radiation corresponding to the experimental observation of three temporally separated sub picosecond pulses.
Author: Margaret Mary Murnane
Publisher:
ISBN:
Category : Laser plasmas
Languages : en
Pages : 292
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Author: Pedro González de Alaiza Martínez
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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The 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.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 45
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This report describes the development of ultra-short pulse laser (USPL) induced terahertz (THz) radiation to image electronic plasmas during electrical breakdown. The technique uses three pulses from two USPLs to (1) trigger the breakdown, (2) create a 2 picosecond (ps, 10 -12 s), THz pulse to illuminate the breakdown, and (3) record the THz image of the breakdown. During this three year internal research program, sub-picosecond jitter timing for the lasers, THz generation, high bandwidth (BW) diagnostics, and THz image acquisition was demonstrated. High intensity THz radiation was optically-induced in a pulse-charged gallium arsenide photoconductive switch. The radiation was collected, transported, concentrated, and co-propagated through an electro-optic crystal with an 800 nm USPL pulse whose polarization was rotated due to the spatially varying electric field of the THz image. The polarization modulated USPL pulse was then passed through a polarizer and the resulting spatially varying intensity was detected in a high resolution digital camera. Single shot images had a signal to noise of %7E3:1. Signal to noise was improved to %7E30:1 with several experimental techniques and by averaging the THz images from %7E4000 laser pulses internally and externally with the camera and the acquisition system (40 pulses per readout). THz shadows of metallic films and objects were also recorded with this system to demonstrate free-carrier absorption of the THz radiation and improve image contrast and resolution. These 2 ps THz pulses were created and resolved with 100 femtosecond (fs, 10 -15 s) long USPL pulses. Thus this technology has the capability to time-resolve extremely fast repetitive or single shot phenomena, such as those that occur during the initiation of electrical breakdown. The goal of imaging electrical breakdown was not reached during this three year project. However, plans to achieve this goal as part of a follow-on project are described in this document. Further modifications to improve the THz image contrast and resolution are proposed, and after they are made, images of photo-induced carriers in gallium arsenide and silicon will be acquired to evaluate image sensitivity versus carrier density. Finally electrical breakdown will be induced with the first USPL pulse, illuminated with THz radiation produced with the second USPL pulse and recorded with the third USPL pulse.
Author: Ki Young Kim
Publisher: BoD – Books on Demand
ISBN: 9537619710
Category : Technology & Engineering
Languages : en
Pages : 470
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Book Description
Research and development in modern optical and photonic technologies have witnessed quite fast growing advancements in various fundamental and application areas due to availability of novel fabrication and measurement techniques, advanced numerical simulation tools and methods, as well as due to the increasing practical demands. The recent advancements have also been accompanied by the appearance of various interdisciplinary topics. The book attempts to put together state-of-the-art research and development in optical and photonic technologies. It consists of 21 chapters that focus on interesting four topics of photonic crystals (first 5 chapters), THz techniques and applications (next 7 chapters), nanoscale optical techniques and applications (next 5 chapters), and optical trapping and manipulation (last 4 chapters), in which a fundamental theory, numerical simulation techniques, measurement techniques and methods, and various application examples are considered. This book deals with recent and advanced research results and comprehensive reviews on optical and photonic technologies covering the aforementioned topics. I believe that the advanced techniques and research described here may also be applicable to other contemporary research areas in optical and photonic technologies. Thus, I hope the readers will be inspired to start or to improve further their own research and technologies and to expand potential applications. I would like to express my sincere gratitude to all the authors for their outstanding contributions to this book.
Author:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 896
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Author: Daniel Mittleman
Publisher: Springer
ISBN: 3540456015
Category : Science
Languages : en
Pages : 351
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The purpose of this book is two-fold. First, the various different methods of accessing the THz range are discussed, with a view to convince the reader that there have been qualitative and significant improvements over older, more conventional techniques. The text makes it clear that these improvements enable practical "real-world" applications of THz technology, in a manner which would not have been possible before. Second, the demonstrations and feasibility tests described serve as compelling evidence of the utility of such devices. Due to the unique characteristics of THz radiation and its interaction with materials, these devices have substantial advantages over other competing technologies in a number of different areas.
Author: Daniel Warren Van Der Weide
Publisher:
ISBN:
Category :
Languages : en
Pages : 280
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