Download or read book Design Analysis and Characterization of Indirectly pumped Terahertz Quantum Cascade Lasers written by Seyed Ghasem Razavipour and published by . This book was released on 2013 with total page 129 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum cascade laser (QCL), as a unipolar semiconductor laser based on intersubband transitions in quantum wells, covers a large portion of the Mid and Far Infrared electromagnetic spectrum. The frequency of the optical transition can be determined by engineering the layer sequence of the heterostructure. The focus of this work is on Terahertz (THz) frequency range (frequency of 1 - 10 THz and photon energy of ~ 4 - 40 meV), which is lacking of high power, coherent, and efficient narrowband radiation sources. THz QCL, demonstrated in 2002, as a perfect candidate of coherent THz source, is still suffering from the empirical operating temperature limiting factor of T [ap] h̳[omega]/kB, which allows this source to work only under a cryogenic system. Most of high performance THz QCLs, including the world record design which lased up to ~ 200 K, are based on a resonant phonon (RP) scheme, whose population inversion is always less than 50%. The indirectly-pumped (IDP) QCL, nicely implemented in MIR frequency, starts to be a good candidate to overcome the aforementioned limiting factor of RP-QCL. A rate equation (RE) formalism, which includes both coherent and incoherent transport process, will be introduced to model the carrier transport of all presented structures in this thesis. The second order tunneling which employed the intrasubband roughness and impurity scattering, was implemented in our model to nicely predict the behavior of the QCL designs. This model, which is easy to implement and fast to calculate, could help us to engineer the electron wavefunctions of the structure with optimization tools. We developed a new design scheme which employs the phonon scattering mechanism for both injecting carrier to the upper lasing state and extracting carrier from lower lasing state. Since there is no injection/extraction state to be in resonance with lasing states, this simple design scheme does not suffer from broadening due to the tunneling. Finally, three different THz IDP-QCLs, based on phonon-photon-phonon (3P) scheme were designed, grown, fabricated, and characterized. The performance of those structures in terms of operating temperature, threshold current density, maximum current density, output optical power, lasing frequency, differential resistance at threshold, intermediate resonant current before threshold, and kBT/h̳[omega] factor will be compared. We could improve the kBT/h̳[omega] factor of the 3P-QCL design from 0.9 in first iteration to 1.3 and the output optical power of the structure from 0.9 mW in first design to 3.4 mW. The performance of the structure in terms of intermediate resonant current and the change in differential resistance at threshold was improved.

Download or read book Characterization and Analysis of Highly Diagonal Terahertz Quantum Cascade Lasers written by Chun Wang Ivan Chan and published by . This book was released on 2010 with total page 157 pages. Available in PDF, EPUB and Kindle. Book excerpt: The as yet unattained milestone of room-temperature operation is essential for establishing Terahertz Quantum Cascade Lasers (THz QCLs) as practical sources of THz radiation. Temperature performance is hypothesized to be limited by upper laser level lifetime reduction due to non-radiative scattering, particularly by longitudinal optical phonons. To address this issue, this work studies highly "diagonal" QCLs, where the upper and lower laser level wave functions are spatially separated to preserve upper laser level lifetime, as well as several other issues relevant to high temperature performance. The highly diagonal devices of this work performed poorly, but the analysis herein nevertheless suggest that diagonality as a design strategy cannot yet be ruled out. Other causes of poor performance in the lasers are identified, and suggestions for future designs are made.

Download or read book Design Fabrication and Characterization of Terahertz Quantum Cascade Lasers written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Design Fabrication and Characterization of Quantum Cascade Terahertz Emitters written by Vinod M. Menon and published by . This book was released on 2001 with total page 230 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Terahertz Time domain Characterization of Amplifying Quantum Cascade Metasurface written by Yue Shen and published by . This book was released on 2019 with total page 67 pages. Available in PDF, EPUB and Kindle. Book excerpt: The THz quantum-cascade vertical-external-cavity surface-emitting-laser (QC-VECSEL) is a recently developed approach for designing high-power, electrically pumped THz lasers with excellent beam quality and broadband tunability. The key component of the QC-VECSEL is an amplifying reflectarray metasurface, based on a subwavelength array of surface radiating metal-metal waveguide antenna elements loaded with QC-laser gain material. Despite its importance, the gain properties of the QC-metasurface are designed by simulation and have only been verified indirectly through observation of the QC-VECSEL lasing characteristics, or by passive FTIR reflectance measurements at room-temperature. THz time-domain spectroscopy (TDS) has been widely used to investigate gain spectra and laser dynamics of THz QC-lasers based on various ridge waveguide geometries. In this thesis, I describe my construction of a THz TDS system and present the first direct spectral measurement using reflection-mode THz TDS of an amplifying QC-metasurface resonant at 2.6 THz under different conditions. The large surface-radiating aperture of the metasurface (1.5 1.5 mm2 in this case) eases free-space TDS measurements compared to ridge waveguide QC-devices with sub-wavelength sized facets.

Download or read book Design and Characterization of a Double transition Quantum Cascade Laser written by Jingyuan Linda Zhang and published by . This book was released on 2012 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Design and Characterization of Quantum Cascade Lasers written by Maytee Lerttamrab and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Development of Terahertz QCLs written by Sushil Kumar (Ph. D.) and published by . This book was released on 2007 with total page 340 pages. Available in PDF, EPUB and Kindle. Book excerpt: The terahertz or the far-infrared frequency range of the electromagnetic spectrum (...) has historically been technologically underdeveloped despite having many potential applications, primarily due to lack of suitable sources of coherent radiation. Following on the remarkable development of mid-infrared (...) quantum-cascade lasers (QCLs) in the past decade, this thesis describes the development of electrically-pumped terahertz quantum-cascade lasers in GaAs/AlsGal_. As heterostructures that span a spectral range of 1.59 - 5.0 THz (...). A quantum-cascade laser (QCL) emits photons due to electronic intersubband transitions in the quantum-wells of a semiconductor heterostructure. The operation of terahertz QCLs at frequencies below the Reststrahlen band in the semiconductor (...), is significantly more challenging as compared to that of the mid-infrared QCLs. Firstly, due to small energy separation between the laser levels various intersubband scattering mechanisms are activated, which make it difficult to selectively depopulate the lower laser level. Additionally, as electrons gain enough kinetic energy in the upper laser level thermally activated longitudinal-optical (LO) phonon scattering reduces the level lifetime and makes it difficult to sustain population inversion at higher temperatures. Secondly, waveguide design for terahertz mode confinement is also more challenging due to higher free-carrier losses in the semiconducting doped regions at the terahertz frequencies. For successful designs reported in this work, the lower radiative state depopulation is achieved by a combination of resonant-tunneling and fast LO phonon scattering, which allow robust operation even at relatively high temperatures. An equally important enabling mechanism for these lasers is the development of metal-metal waveguides, which provide low waveguides losses, and strong mode confinement due to subwavelength mode localization in the vertical dimension. With these techniques some record performances for terahertz QCLs are demonstrated including the highest pulsed operating temperature of 169 K, the highest continuous-wave (cw) operating temperature of 117 K, and the highest optical power output (248 mW in pulsed and 138 mW in cw at 5 K) for any terahertz QCL. Towards the bigger goal of realizing a 1-THz solid-state laser to ultimately bridge the gap between electronic and optical sources of electromagnetic radiation, QCLs with a unique one-well injection scheme, which minimizes intersubband absorption losses that occur at longer wavelengths, are developed. Based on this scheme a QCL operating at 1.59 THz (A - 189 ym) is realized, which is amongst the lowest frequency solid-state lasers that operate without the assistance of a magnetic field. This thesis also reports on the development of distributed-feedback lasers in metal-metal waveguides to obtain single-mode operation, with greater output power and better beam quality. The subwavelength vertical dimension in these waveguides leads to a strongly coupled DFB action and a large reflection from the end-facets, and thus conventional coupled-mode theory is not directly applicable to the DFB design. A design technique with precise control of phase of reflection at the end-facets is developed with the aid of finite-element analysis, and with some additional unique design and fabrication methods, robust DFB operation has been obtained. Single-mode surface-emitting terahertz QCLs operating up to - 150 K are demonstrated, with different grating devices spanning a range of approximately 0.35 THz around v - 3 THz using the same gain medium. A single-lobed far-field radiation pattern, higher output power due to surface-emission, and a relatively small degradation in temperature performance compared to the Fabry-Perot ridge lasers makes these DFB lasers well suited for practical applications that are being targeted by the terahertz quantum-cascade lasers.

Download or read book THz Time Domain Characterization of Amplifying Quantum Cascade Metasurface written by Yue Shen and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Terahertz (THz) quantum cascade lasers (QCLs) are compact electrically pumped unipolar semiconductor laser which can produce a continuous wave radiation of high output power in the range of 1.2 to 5.6 THz. The QC vertical-external-cavity surface-emitting-laser (QC-VECSEL) is an external cavity configuration that supports high-power operation with excellent beam quality and broadband tunability. The key component of the QC-VECSEL is an amplifying reflectarray metasurface, based on a subwavelength array of surface-radiating metal-metal waveguide antenna elements loaded with QC-laser gain material. Despite its importance, up to now the spectral properties of the QC-metasurface have been designed by simulations and have only been verified indirectly through observation of the QC-VECSEL lasing characteristics, or by passive FTIR reflectance measurements at room temperature. Furthermore, design takes place using simulations based upon simplified models for the material loss and the QC-gain, where uncertain Drude model parameters for material losses are used, and the detailed interaction of the intersubband transition with the metasurface is neglected. In the past decade, THz time domain spectroscopy (THz-TDS) has been widely used to investigate gain spectra and laser dynamics of THz QC-lasers based on various ridge waveguide geometries. During my doctoral studies, I designed and built up a reflection-mode THz-TDS system to study amplifying quantum-cascade (QC) metasurface samples as a function of injected current density. The first direct spectral measurements were performed on QC-metasurfaces using reflection-mode THz-TDS. Several different kinds of metasurface were designed that were suitable for study by the THz-TDS system. Extremely strong absorption features for QC-metasurfaces whose resonance frequency designed below 3 THz is measured at zero bias, which is associated with coupling between the metasurface resonance and an intersubband transition within the QC material. In one case, nearly perfect absorption is observed due to the transition from weak to strong light-matter coupling condition. Increase in reflectance are observed as the devices are biased, both due to reduction in intersubband loss and the presence of intersubband gain. Significant phase modulation associated with the metasurface resonance is observed via electrical control for some certain metasurfaces, which may be useful for electrical tuning of QC-VECSEL. These results provide insight into the interaction between the intersubband QC-gain material and the metasurface and modify the design rules for QC-VECSELs for both biased and unbiased regions.

Download or read book Nonlinear Laser Dynamics written by Kathy Lüdge and published by John Wiley & Sons. This book was released on 2012-04-09 with total page 412 pages. Available in PDF, EPUB and Kindle. Book excerpt: A distinctive discussion of the nonlinear dynamical phenomena of semiconductor lasers. The book combines recent results of quantum dot laser modeling with mathematical details and an analytic understanding of nonlinear phenomena in semiconductor lasers and points out possible applications of lasers in cryptography and chaos control. This interdisciplinary approach makes it a unique and powerful source of knowledge for anyone intending to contribute to this field of research. By presenting both experimental and theoretical results, the distinguished authors consider solitary lasers with nano-structured material, as well as integrated devices with complex feedback sections. In so doing, they address such topics as the bifurcation theory of systems with time delay, analysis of chaotic dynamics, and the modeling of quantum transport. They also address chaos-based cryptography as an example of the technical application of highly nonlinear laser systems.

Download or read book Beam Pattern Engineering of Metamaterial Terahertz Quantum cascade Devices written by Philip Wing-Chun Hon and published by . This book was released on 2013 with total page 199 pages. Available in PDF, EPUB and Kindle. Book excerpt: Generation and detection of microwave radiation is done with electronic systems where the underyling processes involve oscillating free charges (such as on an antenna or within a transistor or diode). On the higher energy side of the spectrum, generation and detection of near infrared and visible radiation is achieved via quantum transitions with emission wavelengths that are dictated by the material. Solutions moving up towards the THz regime using microwave based solutions are limited by carrier transit time and RC time-constant limitations. Techniques and solutions moving down toward the THz regime using photonic techniques have emission wavelengths naturally limited by the band gap of the material. However, THz quantum-cascade (QC) lasers, which are an extension of photonic concepts to lower energies, have artificially engineered energy levels and hence emission wavelengths. THz QC-lasers have been demonstrated to operate at frequencies between 1.2 and 5.0 THz and the best high-temperature operation is based upon the metal-metal (MM) waveguide configuration, in which the multiple-quantum well active region is sandwiched between two metal cladding layers, typically separated by 2-10 [mu]m. Soon after the demonstration of MM waveguide QC-lasers, it was recognized that the beam pattern from a conventional cleaved-facet Fabry Pérot (FP) ridge cavity produced a highly divergent beam pattern, characterized by concentric rings in the far field. This thesis presents work on a new approach to tailor the beam pattern of THz MM waveguide QC-devices. Namely, dispersion engineering using metamaterials based on the composite right/left-handed (CRLH) transmission line formalism is adapted to the MM waveguide configuration to realize an entirely new class of devices. Dispersion, radiative loss, and radiation patterns are presented for many newly designed 1-D and 2-D THz QC transmission line metamaterial designs. The first ever active 1-D THz QC transmisison line metamaterial is experimentally characterized and its radiation pattern and polarization closely match theoretical and full-wave finite element method (FEM) simulated predictions. Proven microwave techniques such as circuit, antenna cavity modeling and array factor theory are used to understand the radiative properties of conventional THz QC-lasers. We predict far-field beam patterns and polarizations, approximate cavity quality factors, and associate these properties with individual surfaces or structures of the device. The analysis technique is also applied to the project's 1-D and 2-D THz CRLH QC-devices yielding qualitative agreement with experiments. The first THz design, analysis and experimental verification of a metasur face comprised of an array of passive THz QC transmission lines is presented. By using the cavity model, array factor, circuit and electromagnetic theory a surface impedance model is developed to characterize the metasurface. The surface impedance model reveals waveguide mode dependent radiative coupling with the light line and capacitve/inductive surface impedance. Polarization dependent angle-resolved Fourier transform infrared reflection spectroscopy measurements match the model and full-wave FEM predictions, further assisting the understanding of such devices. To address the broader goal of a directive and scalable THz QC-device, thefeasibility of a 2-D metamaterial inspired QC-laser and an active reflectarray is considered. Finally, preliminary work on a technology enabling active metasurface reflector for a QC vertical external cavity surface emitting laser is discussed.

Download or read book Mid infrared Quantum Cascade Lasers Modeling Fabrication and Characterization written by Luyao Xu and published by . This book was released on 2013 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the past 20 years, mid-infrared Quantum Cascade Lasers (mid-IR QCLs) have been experiencing rapid development and have become practical mid-IR sources for a variety of applications. There is particular technological interest in high efficiency lasers designed for the midwave infrared (MWIR) atmospheric window (3-5 [mu]m) and longwave infrared (LWIR) atmospheric window (8-13 [mu]m). This work presents a systematic study over mid-IR QCLs, including theoractical modeling, device fabrication and characterization. An effective bandstructure calculation method is implemented in this work for active region modeling. A standard process for fabricating mid-IR QCLs has been developed, based on which both LWIR (~ 9 [mu]m) and MWIR (~ 4 [mu]m) QCLs have been successfully demonstrated. Comprehensive testing results are analyzed and discussed, yielding valuable information about the current device design.

Download or read book Theoretical and Computational Design of Terahertz Frequency Quantum Cascade Lasers written by Adam Todd Cooney and published by . This book was released on 2009 with total page 598 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Intersubband Transitions In Quantum Structures written by Roberto Paiella and published by McGraw Hill Professional. This book was released on 2006-05-04 with total page 455 pages. Available in PDF, EPUB and Kindle. Book excerpt: Investigates and outlines the experimental technique of intersubband transitions as a solution. Covers topics such as: intersubband emission in silicon-based quantum structure, quantum dot infrared photodetectors, antimonide, quantum cascade lasers for the 3-5m atmospheric window and more.

Download or read book Handbook of Laser Technology and Applications written by Chunlei Guo and published by CRC Press. This book was released on 2021-06-23 with total page 711 pages. Available in PDF, EPUB and Kindle. Book excerpt: This comprehensive handbook gives a fully updated guide to lasers and laser systems, including the complete range of their technical applications. The first volume outlines the fundamental components of lasers, their properties and working principles. The second volume gives exhaustive coverage of all major categories of lasers, from solid-state and semiconductor diode to fiber, waveguide, gas, chemical, and dye lasers. The third volume covers modern applications in engineering and technology, including all new and updated case studies spanning telecommunications and data storage to medicine, optical measurement, defense and security, nanomaterials processing and characterization.

Download or read book Handbook of Terahertz Technologies written by Ho-Jin Song and published by CRC Press. This book was released on 2015-04-15 with total page 606 pages. Available in PDF, EPUB and Kindle. Book excerpt: Terahertz waves, which lie in the frequency range of 0.1-10 THz, have long been investigated in a few limited fields, such as astronomy, because of a lack of devices for their generation and detection. Several technical breakthroughs made over the last couple of decades now allow us to radiate and detect terahertz waves more easily, which has trigg

Download or read book Optics Letters written by and published by . This book was released on 2002 with total page 806 pages. Available in PDF, EPUB and Kindle. Book excerpt: