Download or read book Broadly Tunable Terahertz Difference Frequency Generation in Mid infrared Quantum Cascade Lasers written by Yifan Jiang (Ph. D. in electrical and computer engineering) and published by . This book was released on 2017 with total page 204 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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

Download or read book Terahertz Generation with Quantum Cascade Lasers written by Karun Vijayraghavan and published by . This book was released on 2014 with total page 226 pages. Available in PDF, EPUB and Kindle. Book excerpt: The terahertz (THz) spectral range is devoid of commercially feasible radiation sources, detectors, and components. In particular, THz sources are bulky, complex to operate, and cost-prohibitive - more suited for a research laboratory than a commercial setting. Developing compact and mass-producible sources in the 1 to 6 THz spectral range will open up new avenues for this technology to make a mainstream societal impact. The focus of this thesis is the development of compact, room-temperature terahertz sources based on quantum cascade lasers (QCL) and quantum well technology. QCLs are semiconductor lasers that operate with high power at mid-infrared (mid-IR) and THz frequencies. THz QCLs are the only mW-level average power sources with spectral coverage from 0.8 to 5 THz. However they only work at cryogenic temperatures because they cannot maintain population inversion across the lasing transition at elevated temperatures. Cryogenic cooling makes these sources cumbersome to operate and expensive to manufacture. Room-temperature operation significantly enhances their commercial appeal and a portion of this dissertation investigated the improvement in THz QCL temperature performance using GaAs-Al0.15Ga0.85As double-phonon resonant active region designs. These devices worked up to 173 K and were a substantial improvement compared to prior implementations of double-phonon resonant designs. Room-temperature THz sources that do not require population inversion across the lasing transition can be engineered by combining the field of nonlinear optics with intersubband transitions in quantum well structures. One method of creating inversionless THz lasing is based upon the principle of Raman gain in semiconductors and this thesis explores the design of an intersubband Raman laser (IRL) with GaAs-Al0.33Ga0.67As heterostructures. The primary focus of this dissertation is developing room-temperature, broadly-tunable, monolithic THz sources based on difference-frequency generation (DFG) in mid-IR QCLs. The source active region is quantum-engineered to provide lasing at mid-IR frequencies, [omega]1 and [omega]2, and simultaneously have giant second-order optical nonlinearity for THz generation at frequency [omega] [subscript THz]=[omega]1-[omega]2. This dissertation developed a Cherenkov emission scheme that produced devices with a narrow emission linewidth, 0.12 mW peak power and tuning from 1.55 to 5.7 THz - the largest tuning bandwidth compared to semiconductor technology of similar size and cost.

Download or read book Mid Infrared and Terahertz Quantum Cascade Lasers written by Dan Botez and published by Cambridge University Press. This book was released on 2023-09-14 with total page 552 pages. Available in PDF, EPUB and Kindle. Book excerpt: Learn how the rapidly expanding area of mid-infrared and terahertz photonics has been revolutionized in this comprehensive overview. State-of-the-art practical applications are supported by real-life examples and expert guidance. Also featuring fundamental theory enabling you to improve performance of both existing and future devices.

Download or read book Mid Infrared and Terahertz Quantum Cascade Lasers written by Dan Botez and published by Cambridge University Press. This book was released on 2023-06-30 with total page 551 pages. Available in PDF, EPUB and Kindle. Book excerpt: A state-of-the-art overview of this rapidly expanding field, featuring fundamental theory, practical applications, and real-life examples.

Download or read book Terahertz Difference Frequency Generation Quantum Cascade Lasers with Improved Terahertz Out coupling Efficiency written by Jae Hyun Kim and published by . This book was released on 2019 with total page 200 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Widely Tunable Terahertz Semiconductor Laser Sources written by Aiting Jiang and published by . This book was released on 2015 with total page 204 pages. Available in PDF, EPUB and Kindle. Book excerpt: Terahertz Quantum Cascade Lasers (THz QCLs) and Terahertz Difference Frequency Generation Quantum Cascade Laser sources (DFG-QCLs) are two types of semiconductor THz radiation sources that are compact and amenable to production in mass quantities. THz QCL can generate over 1W of power under cryogenic temperatures, while THz DFG-QCL can be operated under room temperature over 1mW level output. For either case, widely tunable solution is highly desired for spectroscopy applications. For THz QCLs, operation is still limited to cryogenic temperature and broad tuning is not available. Our experimental study shows that using variable barriers is a viable approach to enhance the design space for THz QCLs. We also propose to tune the spectral output of these devices using an optically projected variable distributed feedback grating. Tuning will be achieved by changing the projected grating period. Preliminary experimental results support the idea but higher pumping light intensity is required for this method to work. For THz DFG-QCLs, very broad tuning in 1-6 THz range has been demonstrated using rotating diffraction grating in an external cavity setup. Similar tuning range can also be achieved in a monolithic configuration. Based on the previous work which demonstrated an electrical monolithic tuner with 580 GHz tuning range, we design and test in this dissertation a linear array of 10 DFG-QCL devices to cover a 2 THz tuning range. An independent gain control scheme is developed to achieve high yield (~100%) of individual device. It is implemented via independent current pumping of two electrically isolated sections. Surface DFB grating and independent current pumping scheme used in our DFG QCLs is found to be useful for mid-IR QCL array sources. We propose a longitudinal integration scheme of multiple grating sections. It enables a single ridge to emit single mode radiation at different wavelengths upon selection. This helps to reduce mid-IR QCL array far field span. We demonstrated single ridge devices that can emit 2 or 3 different wavelengths upon selection.

Download or read book Broadly Tunable Mid infrared Quantum Cascade Lasers for Spectroscopic Applications written by Richard Maulini and published by . This book was released on 2006 with total page 133 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Nonlinear Photonics in Mid infrared Quantum Cascade Lasers written by Louise Jumpertz and published by Springer. This book was released on 2017-08-31 with total page 152 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis presents the first comprehensive analysis of quantum cascade laser nonlinear dynamics and includes the first observation of a temporal chaotic behavior in quantum cascade lasers. It also provides the first analysis of optical instabilities in the mid-infrared range. Mid-infrared quantum cascade lasers are unipolar semiconductor lasers, which have become widely used in applications such as gas spectroscopy, free-space communications or optical countermeasures. Applying external perturbations such as optical feedback or optical injection leads to a strong modification of the quantum cascade laser properties. Optical feedback impacts the static properties of mid-infrared Fabry–Perot and distributed feedback quantum cascade lasers, inducing power increase; threshold reduction; modification of the optical spectrum, which can become either single- or multimode; and enhanced beam quality in broad-area transverse multimode lasers. It also leads to a different dynamical behavior, and a quantum cascade laser subject to optical feedback can oscillate periodically or even become chaotic. A quantum cascade laser under external control could therefore be a source with enhanced properties for the usual mid-infrared applications, but could also address new applications such as tunable photonic oscillators, extreme events generators, chaotic Light Detection and Ranging (LIDAR), chaos-based secured communications or unpredictable countermeasures.

Download or read book Spectroscopic Applications of Terahertz Quantum Cascade Lasers written by Tasmim Alam and published by Cuvillier Verlag. This book was released on 2020-10-29 with total page 132 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Design and Modeling of High Temperature Terahertz Quantum Cascade Lasers written by Benjamin Adams Burnett and published by . This book was released on 2016 with total page 223 pages. Available in PDF, EPUB and Kindle. Book excerpt: The portion of the electromagnetic spectrum between roughly 300 GHz and 10 THz is nicknamed the "THz Gap" because of the enormous difficulty encountered by researchers to devise practical sources covering it. Still, the quantum cascade laser (QCL) has emerged over recent years as the most promising approach to a practical source in the 1-5 THz range. First developed in the higher-frequency mid-IR, where they are now widely available, QCLs were later extended to the THz where a host of greater design challenges awaited. Lasing in QCLs is based on intersubband optical transitions in semiconductor quantum wells, the energy of which can be chosen by design ("bandstructure engineering"). However, simply building a THz optical transition is insufficient; a good design must also produce significant population inversion by the applied cascading electron current, and this requires deep understanding of the transport physics. So far, no THz QCL has operated above the temperature of 200 K, even though the reasons prohibiting high temperature operation are well known. The goal of this Thesis is to put novel ideas for high-temperature operation of THz QCL active regions through rigorous theoretical testing. The central enabling development is a density-matrix-based model of transport and optical properties tailored for use in QCLs, which is general enough that widely varying design concepts can be tested using the same core principles. Importantly, by simulating QCLs more generally, fewer a priori assumptions are required on part of the researcher, allowing for the true physics to emerge on its own. It will be shown that this gives rise to new and useful insights that will help to guide the experimental efforts towards realization of these devices. One specific application is a quantum dot cascade laser (QDCL), a highly ambitious approach in which the electrons cascade through a series of quantum dots rather than wells. Benefits are expected due to the suppression of nonradiative scattering, brought about by the discrete spectrum of electronic states. However, this in turn leads to a highly different physics of transport and effects that are not well understood, even in the case of perfect materials. This work will show that while the benefits are clear, naive scaling of existing QCL designs to the quantum dot limit will not work. An alternative strategy is given based on a revised understanding of the nature of transport, and is put to a test of practicality in which the effects of quantum dot size inhomogeneity are estimated. Another application is to the already existing method of THz difference frequency generation in mid-IR QCLs, which occurs via a difference-frequency susceptibility $\chi^{(2)}$ in the active region itself. For this purpose, the model is extended to enable a coherent and nonperturbative calculation of optical nonlinearities. First, the generality of the method is displayed through the emergence of exotic nonlinear effects, including electromagnetically-induced transparency, in mock quantum-well systems. Then, the modeling concepts are applied to the real devices, where two new and important mechanisms contributing to $\chi^{(2)}$ are identified. Most importantly, it is predicted that the QCL acts as an extremely fast photodetector of itself, giving rise to a current response to the mid-IR beatnote that provides a better path forward to the generation of frequencies below ~2 THz. Finally, the fundamentals of density matrix transport theory for QCLs are revisited to develop a model for conventional THz QCL designs eliminating the usual phenomenological treatment of scattering. The new theory is fully developed from first principles, and in particular sheds light on the effects of scattering-induced electron localization. The versatility of the model is demonstrated by successful simulation of varying active region designs.

Download or read book High Average Brightness Broad Area Quantum Cascade Lasers written by Matthew Michael Suttinger and published by . This book was released on 2020 with total page 95 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum Cascade Lasers are a novel semiconductor light source with the unique property of wavelength tunability over the mid-infrared and terahertz range of frequencies. Advances since their first demonstration in 1994 have led to highly efficient designs capable of continuous room temperature operation. In lieu of increased advances in laser core efficiency, power scaling with broad area quantum cascade lasers has demonstrated enhanced continuous power. This initial work is used as a starting point for continuing advances in average brightness of quantum cascade lasers. A figure of merit calculation reliably predicts to within parts in thousands the qualitative beam profile of continuously driven and high duty cycle devices. Further, a model is developed to project performance not only in continuously driven conditions, but also in variable duty cycles. This is combined with the figure of merit calculation to guide designs for optimized average brightness.

Download or read book Terahertz Local Oscillator Via Difference Frequency Generation in III V Semiconductors Using Frequency Stabilized Lasers written by Greg Herman and published by . This book was released on 2013 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt: Terahertz (THz) heterodyne receiver systems are required by NASA to monitor gas concentrations related to the Earth's ozone depletion. To this end, NASA needs compact, solid state, tunable THz local oscillators. THz LOs have been developed using three means: 1) All-electronic LOs using mixers in combination with Gunn oscillators, 2) Hybrid Photo-electronic LOs using a cw analog of the Auston switch, and 3) All-photonic THz LOs using coherent sources, such as vapor lasers or solid-state Quantum Cascade Lasers, and down converting lasers using nonlinear crystals. In this dissertation, we began with two frequency stabilized Nd:YAG lasers, locked to a common reference cavity, as a starting point to having a stable input into a nonlinear optical frequency conversion system. Following this, we explored the nonlinear crystals useful for THz generation, and the phasematching schemes that could be employed by each. We concluded by settling on highly insulating III-V semiconductor crystals as the proper choice of nonlinear element, and put together a new phasematching method that is most useful for them.

Download or read book Frequency Tunable Terahertz Quantum Cascade Lasers written by Iman Kundu and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Terahertz Metrology written by Mira Naftaly and published by Artech House. This book was released on 2015-01-01 with total page 386 pages. Available in PDF, EPUB and Kindle. Book excerpt: This new book describes modern terahertz (THz) systems and devices and presents practical techniques for accurate measurement with an emphasis on evaluating uncertainties and identifying sources of error. This is the first THz book on the market to address measurement methodologies and issues -- perfect for practitioners and aspiring practitioners wishing to learn good measurement practice and avoid pitfalls. This book provides a brief review of different THz systems and devices, followed by chapters detailing the measurement issues encountered in using each of the main types of THz systems, and a guide to performing measurements rigorously. Particular attention is given to evaluating uncertainties, and recognizing potential sources of errors. The main focus is on time-domain spectroscopy, by far the most widely used technique. Readers are also presented with examples of applications with the emphasis on utility, both in research and in industry.

Download or read book Thermal and Waveguide Optimization of Broad Area Quantum Cascade Laser Performance written by Matthew Michael Suttinger and published by . This book was released on 2017 with total page 47 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum Cascade Lasers are a novel source of coherent infrared light, unique in their tunability over the mid-infrared and terahertz range of frequencies. Advances in bandgap engineering and semiconductor processing techniques in recent years have led to the development of highly efficient quantum cascade lasers capable of room temperature operation. Recent work has demonstrated power scaling with broad area quantum cascade lasers by increasing active region width beyond the standard ~10 [micrometer]. Taking into account thermal effects caused by driving a device with electrical power, an experimentally fitted model is developed to predict the optical power output in both pulsed and continuous operation with varying device geometry and minor changes to quantum cascade laser active region design. The effects of the characteristic temperatures of threshold current density and slope efficiency, active region geometry, and doping, on output power are studied in the model. The model is then used to refine the active region design for increased power out in continuous operation for a broad area design. Upon testing the new design, new thermal effects on rollover current density are observed. The model is then refined to reflect the new findings and more accurately predict output power characteristics.

Download or read book Quantum Cascade Lasers Based on Intra cavity Frequency Mixing written by Min Jang and published by . This book was released on 2012 with total page 248 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum cascade lasers (QCLs) operate due to population inversion on intersubband in unipolar mutiple-quantum-well (MQW) heterostructure. QCLs are considered one of the most flexible and powerful light semiconductor sources in the mid- and far-infrared (IR) wavelength range, covering most of the critical spectral regions relevant to IR applications. InGaAs/InAlAs/InP QCLs are the only semiconductor lasers capable of continuous wave (CW) operation at room temperature (RT) in the spectral range 3.4-12 micron. This dissertation details the development of RT QCLs based on passive nonlinear coupled-quantum-well structures monolithically integrated into mid-IR QCLs to provide a giant nonlinear response for the pumping frequency. The primary focus of short-wavelength approach in this dissertation is to develop of RT InGaAs/InAlAs/InP QCLs for lamda=2.5-3.7 micron region, based on quasi-phase-matched intracavity second harmonic generation (SHG) associated with intersubband transition. Intersubband optical transition can be engineered by the choice of quantum well and barrier thicknesses to provide the appropriate energy levels, optical dipole matrix elements, and electron scattering rates amongst other parameters. Thus, aside from their linear optical properties, resonant intersubband transitions in coupled QW's can also be designed to produce nonlinear optical medium with giant nonlinear optical susceptibilities. In long-wavelength region, at high temperature, the population inversion is reduced between the upper and lower laser levels due to the longitudinal optical (LO) phonon scattering of thermal carriers in the upper laser state and the thermal backfilling of carriers into the lower laser level from the injector state. This dissertation aims to improve an alternative approach for THz QCL sources based on intra-cavity difference frequency generation (DFG) in dual-wavelength mid-IR QCLs with a passive nonlinear structure, designed for giant optical nonlinearity. Further studies describe that Cerenkov DFG scheme allows for extraction of THz radiation along the whole length of the laser waveguide and provides directional THz emission in 1.2-4.5 THz range. An important requirement for many applications, like chemical sensing and molecular spectroscopy, is single-mode emission. We demonstrate single-mode RT DFG THz QCLs operation in 1-5 THz region by employing devices as integrated dual-period DFB lasers, where efficient solid state RT sources do not exist.

Download or read book Encyclopedia of Modern Optics written by Bob D. Guenther and published by Academic Press. This book was released on 2018-02-14 with total page 2253 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Encyclopedia of Modern Optics, Second Edition, Five Volume Set provides a wide-ranging overview of the field, comprising authoritative reference articles for undergraduate and postgraduate students and those researching outside their area of expertise. Topics covered include classical and quantum optics, lasers, optical fibers and optical fiber systems, optical materials and light-emitting diodes (LEDs). Articles cover all subfields of optical physics and engineering, such as electro-optical design of modulators and detectors. This update contains contributions from international experts who discuss topics such as nano-photonics and plasmonics, optical interconnects, photonic crystals and 2D materials, such as graphene or holy fibers. Other topics of note include solar energy, high efficiency LED’s and their use in illumination, orbital angular momentum, quantum optics and information, metamaterials and transformation optics, high power fiber and UV fiber lasers, random lasers and bio-imaging. Addresses recent developments in the field and integrates concepts from fundamental physics with applications for manufacturing and engineering/design Provides a broad and interdisciplinary coverage of specialist areas Ensures that the material is appropriate for new researchers and those working in a new sub-field, as well as those in industry Thematically arranged and alphabetically indexed, with cross-references added to facilitate ease-of-use