Frequency Control of Terahertz Quantum Cascade Lasers PDF Download
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Author: Thomas Folland
Publisher:
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Languages : en
Pages :
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Author: Thomas Folland
Publisher:
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Category :
Languages : en
Pages :
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Author: Marc Ruben Mertens
Publisher:
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Category :
Languages : en
Pages : 0
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Author: Tasmim Alam
Publisher: Cuvillier Verlag
ISBN: 3736962975
Category : Science
Languages : en
Pages : 132
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Quantum cascade lasers (QCLs) are attractive for high-resolution spectroscopy because they can provide high power and a narrow linewidth. They are particularly promising in the terahertz (THz) range since they can be used as local oscillators for heterodyne detection as well as transmitters for direct detection. However, THz QCL-based technologies are still under development and are limited by the lack of frequency tunability as well as the frequency and output power stability for free-running operation. In this dissertation, frequency tuning and linewidth of THz QCLs are studied in detail by using rotational spectroscopic features of molecular species. In molecular spectroscopy, the Doppler eff ect broadens the spectral lines of molecules in the gas phase at thermal equilibrium. Saturated absorption spectroscopy has been performed that allows for sub-Doppler resolution of the spectral features. One possible application is QCL frequency stabilization based on the Lamb dip. Since the tunability of the emission frequency is an essential requirement to use THz QCL for high-resolution spectroscopy, a new method has been developed that relies on near-infrared (NIR) optical excitation of the QCL rear-facet. A wide tuning range has been achieved by using this approach. The scheme is straightforward to implement, and the approach can be readily applied to a large class of THz QCLs. The frequency and output stability of the local oscillator has a direct impact on the performance and consistency of the heterodyne spectroscopy. A technique has been developed for a simultaneous stabilization of the frequency and output power by taking advantage of the frequency and power regulation by NIR excitation. The results presented in this thesis will enable the routine use of THz QCLs for spectroscopic applications in the near future.
Author: Andriy Danylov
Publisher:
ISBN:
Category : Lasers
Languages : en
Pages : 266
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Author: Matteo Perenzoni
Publisher: Springer
ISBN: 9400738374
Category : Science
Languages : en
Pages : 257
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This book covers the latest advances in the techniques employed to manage the THz radiation and its potential uses. It has been subdivided in three sections: THz Detectors, THz Sources, Systems and Applications. These three sections will allow the reader to be introduced in a logical way to the physics problems of sensing and generation of the terahertz radiation, the implementation of these devices into systems including other components and finally the exploitation of the equipment for real applications in some different field. All of the sections and chapters can be individually addressed in order to deepen the understanding of a single topic without the need to read the whole book. The THz Detectors section will address the latest developments in detection devices based on three different physical principles: photodetection, thermal power detection, rectification. The THz Sources section will describe three completely different generation methods, operating in three separate scales: quantum cascade lasers, free electron lasers and non-linear optical generation. The Systems and Applications section will take care of introducing many of the aspects needed to move from a device to an equipment perspective: control of terahertz radiation, its use in imaging or in spectroscopy, potential uses in security, and will address also safety issues. The text book is at a level appropriate to graduate level courses up to researchers in the field who require a reference book covering all aspects of terahertz technology.
Author: Hajime Asahi
Publisher: John Wiley & Sons
ISBN: 111935501X
Category : Science
Languages : en
Pages : 510
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Covers both the fundamentals and the state-of-the-art technology used for MBE Written by expert researchers working on the frontlines of the field, this book covers fundamentals of Molecular Beam Epitaxy (MBE) technology and science, as well as state-of-the-art MBE technology for electronic and optoelectronic device applications. MBE applications to magnetic semiconductor materials are also included for future magnetic and spintronic device applications. Molecular Beam Epitaxy: Materials and Applications for Electronics and Optoelectronics is presented in five parts: Fundamentals of MBE; MBE technology for electronic devices application; MBE for optoelectronic devices; Magnetic semiconductors and spintronics devices; and Challenge of MBE to new materials and new researches. The book offers chapters covering the history of MBE; principles of MBE and fundamental mechanism of MBE growth; migration enhanced epitaxy and its application; quantum dot formation and selective area growth by MBE; MBE of III-nitride semiconductors for electronic devices; MBE for Tunnel-FETs; applications of III-V semiconductor quantum dots in optoelectronic devices; MBE of III-V and III-nitride heterostructures for optoelectronic devices with emission wavelengths from THz to ultraviolet; MBE of III-V semiconductors for mid-infrared photodetectors and solar cells; dilute magnetic semiconductor materials and ferromagnet/semiconductor heterostructures and their application to spintronic devices; applications of bismuth-containing III–V semiconductors in devices; MBE growth and device applications of Ga2O3; Heterovalent semiconductor structures and their device applications; and more. Includes chapters on the fundamentals of MBE Covers new challenging researches in MBE and new technologies Edited by two pioneers in the field of MBE with contributions from well-known MBE authors including three Al Cho MBE Award winners Part of the Materials for Electronic and Optoelectronic Applications series Molecular Beam Epitaxy: Materials and Applications for Electronics and Optoelectronics will appeal to graduate students, researchers in academia and industry, and others interested in the area of epitaxial growth.
Author: Yifan Jiang (Ph. D. in electrical and computer engineering)
Publisher:
ISBN:
Category :
Languages : en
Pages : 204
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Room-temperature terahertz (THz) sources analogous to diode lasers in the near-infrared/visible or quantum cascade lasers (QCL) in the mid-infrared (mid-IR), i.e., electrically pumped, compact, widely tunable, and suitable for low-cost production, are highly desired for feasible and inexpensive THz systems. This dissertation focuses on demonstrating broadly tunable, room-temperature THz systems based on intra-cavity difference frequency generation (DFG) in mid-IR QCLs with improved spectral capability for versatile applications. Spectral control using an external cavity provides the widest tuning range and is favored for real-world applications. DFG-THz could be spectrally tuned by either tuning one mid-IR pump or by tuning both mid-IR pumps together. I built a Littrow-type, external cavity THz DFG-QCL system that generated spectral tunable THz radiation by fixing one mid-IR pump frequency with an integrated DFB grating on top of the QCL structure and tuning the other mid-IR pump frequency with an external grating, thus demonstrating record broadband narrow linewidth THz frequency tuning from 1.2 to 5.9 THz. A Cherenkov waveguide is used in this system to extract THz radiation through the semi-insulating InP substrate; however, InP has dispersion in 1–6 THz, resulting in steering far field profiles for different THz frequencies. Replacing the InP substrate with high-resistance silicon through an adhesive bonding process solved the beam steering problem of this THz DFG-QCL system. I also built a double-Littrow, external cavity DFG-THz system that tunes both mid-IR pump frequencies using two external diffraction gratings. Such a system allows performing a comprehensive spectroscopic study of the optical nonlinearity and its dependence on the mid-infrared pump frequencies. Our work shows that the terahertz generation efficiency can vary by a factor of two or more, depending on the spectral position of the mid-infrared pumps, even for a fixed THz difference frequency. Using this system, we investigated different active region designs: bound-to-continuum, continuum-to-continuum, three-phonon-resonance, and dual-upper-state active region design. Our studies show THz DFG-QCL based a bound-to-continuum active region with gain centered around 15 μm has an order of magnitude enhancement of mid-IR to THz conversion efficiency, which provides a trend for future improvement of the power performance of THz DFG-QCLs
Author: Tsung-Yu Kao
Publisher:
ISBN:
Category :
Languages : en
Pages : 208
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The terahertz (THz) frequency range (300 GHz to 10 THz, wavelength 30-1000 [mu]m), despite having many potential applications, is technologically relatively underdeveloped mainly because of the lack of suitable coherent radiation sources when compared with nearby electromagnetic radiation spectrum. The invention of the THz quantum cascade laser, a electronically-pumped semiconductor heterostructure which emits photons from electronic intersubband transitions, provides the first solidstate fundamental oscillator at the frequency range from 1.2 to 5.1 THz. Due to the subwavelength confinement nature of the metal-metal waveguide used in most of the THz QC lasers, far-field beam patterns from lasers with simple Fabry-Perot waveguides are divergent and far from ideal Gaussian beams. The first part of this thesis describes the development of single-mode THz QC lasers on metal-metal waveguides. Starting with the corrugated third-order DFB laser-a clever laser structure which utilizes end-fire array effect to achieve low divergence beam patterns-several applications using densely-packed third-order DFB laser arrays, such as frequency agile sources for THz swept-source optical tomography and local oscillators for THz heterodyne receivers with precise frequency control, have been investigated. With the improved design rules and fabrication techniques, 830 GHz single-mode frequency coverage on a monolithic multicolor DFB laser array has been achieved. The origin of the deterioration in far-field beam patterns and power outputs in long third-order DFB lasers is then identified. This finding leads to a modified third-order DFB laser structure which can achieve perfect phase-matching (PM) condition, resulting in scalable power output and even lower beam divergence when compared with that of a conventional third-order DFB laser. Radiations from up to 151 laser sectors are phase-locked to form a single-lobe beam pattern with divergence ~ 6 x 11° and ~13 mW pulsed power at the end-fire direction. This approach substantially increases the usable length of a third-order DFB laser while keeping a high slope efficiency (140 mW/A). Later development applies the concept of microstrip antenna-a structure commonly used in microwave engineering-to THz photonics devices. By coupling the microstrip antenna to each grating aperture of a perfectly phase-matched DFB laser, the radiation impedance of the laser can now be tuned to enhance the overall emission efficiency. This novel genre of DFB laser achieves > 8 mW pulsed power (10% duty-cycle) at 12 K with beam divergence as low as 12.5 x 12.5' and maximum lasing temperature Tmax = 109 K (pulsed) and 77 K (c.w.) with the highest slope efficiency (~450 mW/A) and wall-plug efficiency (0.57%) of all THz DFB laser sources. The second part of the thesis then focuses on the development of the first light amplifier in THz frequency under Fabry-Perot amplifier (FPA) scheme. Although amplification at terahertz frequency in quantum cascade structures has been demonstrated under the transient state or in a integrated platform, none of them is suitable for amplifying continuous-wave free-space THz radiations. The proposed amplifier is consisted of an array of short-cavity surface-emitting second-order distributed feedback lasers arranged in a two-dimensional grid which are operated marginally beneath their lasing thresholds. A overall system power gain of ~5.6x = 7.5 dB at ~3 THz is obtained with ~1 GHz bandwidth. The free-space THz light amplifier can be used as the pre-amplifier for a THz heterodyne receiver system to reduce the receiver system noise, or be placed on the focal plane of a THz imaging system to enhance the signal-to-noise ratio of the image and reduce the acquisition time. A new locking mechanism for two-dimensional phase-locked laser arrays based on antenna mutual-coupling is also proposed and then successfully demonstrated in the THz frequency using short-cavity DFB THz lasers. Up to 37 lasers are phase-locked to deliver 6.5 mW single-mode pulsed power (4% duty-cycle) at 3 THz with symmetric beam pattern ( 10 x 10°). This new coupling scheme can be extended to other electromagnetic systems with sub-wavelength confined elements such as plasmonic lasers and nanolasers. This thesis also reports the development of fabrication techniques required to bring the aforementioned novel THz cavity designs from concepts to reality which include a high aspect ratio ( 1:10) anisotropic reactive-ion etch on GaAs which is compatible with the metal-metal waveguide platform and the procedure to create airbridge structures by selectively removing the dielectric materials beneath the metal contacts.
Author: Iman Kundu
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Author: Elias Munoz Merino
Publisher: Trans Tech Publications Ltd
ISBN: 3035706530
Category : Technology & Engineering
Languages : en
Pages : 186
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During the last 25 years, the behavior of donors in III-V alloys has been the subject of a very extensive research effort. The research emphasis on AlGaAs compounds is motivated by the industrial importance of AlGaAs/GaAs heterojunction based devices. As seeing it now, "the DX center problem", the behavior of donors in III-V alloys, has shown to be unexpectedly difficult to understand. To determine the microscopic nature of the DX center is still a challenging problem.
