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 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 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 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 Terahertz Quantum Cascade Lasers written by Saeed Fathololoumi and published by . This book was released on 2010 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Mode locking Actif Et Contr le Des Propri t s Spectrales Des Lasers Cascade Quantique T rahertz written by Pierre Gellie and published by . This book was released on 2012 with total page 155 pages. Available in PDF, EPUB and Kindle. Book excerpt: La mise au pint de sources térahertz (THz) dont les propriétés spectrales sont contrôlées est devenu un enjeu important dans plusieurs domaines. Notamment pour des applications comme la spectroscopie de haute résolution, l'imagerie avec haut rapport signal sur bruit ou bien la détection hétérodyne de grande sensibilité. C'est dans ce contexte que se situent mes travaux de thèse. En particulier je me suis penché sur les sources laser à cascade quantique (LCQ) Thz. Dans un premier temps, j'ai montré comment, en modulant un LCQ à une fréquence proche de l'intervalle spectral libre, l'on obtient le verrouillage mutuel des modes du LCQ. Ensuite, j'ai développé une technique de verrouillage de phase du LCQ se basant sur un laser femto-seconde à 1550nm et une détection électro-optique. J'ai ainsi montré que, lorsque la boucle de verrouillage est fermée, la largeur spectrale d'un LCQ à 2.5THZ est inférieure à 1Hz. J'ai ensuite démontré, grâce à une technique optique asynchrone, que l'on peut échantillonner le champ électrique émis par un LCQ fonctionnant en régime de verrouillage de modes. J'ai ainsi pu mesurer une durée impulsion de 10ps pour un LCQ ayant 10 modes longitudinaux au-dessus du seuil, avec un pas d'échantillonnage de 2.3ps. Dans le dernier chapitre de la thèse je me suis intéressé au développement d'une cavité étendue à base d'un LCQ THz. Dans un premier temps, j'ai démontré que la réfléctivité d'une facette d'un LCQ peut être réduite à quelques pourcents en polissant celle-ci à l'angle de Brewster ou bien en déposant une couche antireflet à base de Parylène. Enfin, j'ai développé des LCQ à contre-réaction répartie, afin d'obtenir une émission monomode à haute puissance en régime continu.

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 Design and Simulation of Terahertz Surface Emitting Quantum Cascade Lasers written by Martin F. Schubert and published by . This book was released on 2005 with total page 94 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Frequency Stabilization of a Single Mode Terahertz Quantum Cascade Laser to the Kilohertz Level written by and published by . This book was released on 2009 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: A simple analog locking circuit was shown to stabilize the beat signal between a 2.408 THz quantum cascade laser and a CH2DOH THz CO2 optically pumped molecular laser to 3-4 kHz (FWHM). This is approximately a tenth of the observed long-term (t ~ sec) linewidth of the optically pumped laser showing that the feedback loop corrects for much of the mechanical and acoustic-induced frequency jitter of the gas laser. The achieved stability should be sufficient to enable the use of THz quantum cascade lasers as transmitters in short-range coherent transceivers.

Download or read book Terahertz Quantum cascade Lasers for Spectroscopic Applications written by Benjamin Malte Röben and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 Low Frequency and Circuit Based Quantum Cascade Lasers written by Christoph Walther and published by Sudwestdeutscher Verlag Fur Hochschulschriften AG. This book was released on 2011 with total page 244 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum cascade lasers are unipolar semiconductor lasers based on intersubband transitions in quantum wells. They have shown laser operation from above 100 THz down to the terahertz region and are promising sources for the terahertz region (0.3-10 THz) which is lacking of efficient narrowband radiation sources. A low frequency quantum cascade laser design is developed that faces the emerging challenges when the photon energy approaches the broadening of the energy levels. A record lowest operation frequency of 1.2 THz is demonstrated. A hybrid laser-oscillator for the terahertz is developed in the second part of this work, consisting of an optical gain medium and an electronic resonator. The resonator is an inductor-capacitor resonant circuit. The so called circuit based laser has the property of being a deep sub-wavelength sized microcavity laser. The effective mode volume is among the smallest for electrically pumped lasers. The circuit based resonator in combination with an active region could lead to a class of new devices to generate and manipulate terahertz radiation that exploit cavity quantum electrodynamic effects.

Download or read book The Development and Applications of Terahertz Quantum Cascade Lasers written by Raed Hussain S. Alhathlool and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Development of terahertz quantum cascade lasers as sources for heterodyne receivers written by and published by . This book was released on 2012 with total page 107 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Gain in Terahertz Quantum Cascade Lasers written by M. Houghton and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book High Power and High Efficiency Operation of Terahertz Quantum Cascade Lasers at 3 3 THz Supported by the National Basic Research Program of China Under Grant Nos 2014CB339803 and 2013CB632801 and the National Natural Science Foundation of China Under Grant written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract : A high-power and high-efficiency GaAs/AlGaAs-based terahertz (THz) quantum cascade laser structure emitting at 3.3 THz is presented. The structure is based on a hybrid bound-to-continuum transition and resonant-phonon extraction active region combined with a semi-insulating surface-plasmon waveguide. By optimizing material structure and device processing, the peak optical output power of 758 mW with a threshold current density of 120 A/cm 2 and a wall-plug efficiency of 0.92% at 10K and 404mW at 77K are obtained in pulsed operation. The maximum operating temperature is as high as 115 K. In the cw mode, a record optical output power of 160 mW with a threshold current density of 178 A/cm 2 and a wall-plug efficiency of 1.32% is achieved at 10 K.

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.