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 High Power efficiency Terahertz Quantum Cascade Laser Project Supported by the National Basic Research Program of China Grant Nos 2014CB339803 and 2013CB632801 the Special funded Program on National Key Scientific Instruments and Equipment Development China Grant No 2011YQ13001802 04 and the National Natural Science Foundation of China Grant No 61376051 written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Very Low Threshold Operation of Quantum Cascade Lasers Project Supported by the National Basic Research Program of China Grant Nos 2013CB632801 and 2013CB632803 the National Natural Science Foundation of China Grant Nos 61306058 61274094 and 61435014 and the Beijing Natural Science Foundation Grant No 4144086 written by and published by . This book was released on 2015 with total page 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 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 A Broadband Pulsed External Cavity Quantum Cascade Laser Operating Near 6 9 m Supported by the National Natural Science Foundation of China Under Grant Nos 11174098 and 11574107 and the Self Determined Research Funds of Central China Normal University Under Grant No CCNU15A02034 written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book From High Power Terahertz Quantum Cascade Lasers to Terahertz Light Amplifiers written by Tsung-Yu Kao and published by . This book was released on 2014 with total page 208 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

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 Theoretical Investigation on Generating Terahertz Radiation from Gas Plasma Induced by Three color Ultrashort Lasers Project Supported by the Wuhan Applied Basic Research Project China Grant No 20140101010009 the National Natural Science Foundation of China Grant Nos 61177095 61475054 and 61405063 the Natural Science Foundation of Hubei Province China Grant Nos 2012FFA074 and 2013BAA002 the Fundamental Research Funds for the Central Universities China Grant Nos 2013KXYQ004 2014ZZGH021 and 2014QN023 and the Technology Innovation Foundation from Innovation Institute of Huazhong University of Science and Technology China Grant No CXY13Q015 written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 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 High Temperature and High Power Terahertz Quantum Cascade Lasers written by and published by . This book was released on 2007 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Development of III V Terahertz Quantum Cascade Lasers written by and published by . This book was released on 2005 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt: A very successful Phase I project on semiconductor THz laser has been carried out. Several innovative techniques have been demonstrated during the performance of this work. The most significant concept being a different approach to how the laser should be pumped, resulting in more efficient THz output generation. We called this concept Separate Electrical and Waveguide (SEW) structure that circumvents the radiation absorption in the doped waveguide region in a conventional THz device, leading to lower threshold and higher temperature operation. In addition, we have developed an electrical measurement to detect lasing threshold, and a packaging technique for solid, effective thermal contact during movement.

Download or read book High Power Dual End Pumped Actively Q Switched Ho YAG Ceramic Laser Supported by the National Natural Science Foundation of China Under Grant Nos 61308009 61405047 and 50990301 the China Postdoctoral Science Foundation Funded Project Under Grant No 2015T80339 the Fundamental Research Funds for the Central Universities Under Grant No HIT NSRIF 2015042 and the Science Fund for Outstanding Youths of Heilongjiang Province Under Grant No JQ201310 written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract : We present a high-power Ho:YAG ceramic laser pumped at 1908 nm. Using a dual-end-pumped structure, the maximum continuous-wave output power of 48 W is obtained, corresponding to a slope efficiency of 70.4% with respect to the absorbed pump power. At actively Q-switched mode, the maximum average output power of 46 W and the minimum pulse width of 21 ns are achieved at a pulse repetition frequency of 20 kHz, corresponding to a peak power of approximately 109.5 kW. In addition, the beam-quality M 2 factor is found to be 1.4 at the maximum output power.

Download or read book Development of Terahertz Quantum cascade VECSELs written by Christopher Curwen and published by . This book was released on 2019 with total page 184 pages. Available in PDF, EPUB and Kindle. Book excerpt: Terahertz (THz) quantum-cascade lasers (QCLs) are an emerging semiconductor source of compact, high-power THz radiation. Though first realized more than 15 years ago, THz QCLs continue to suffer from poor beam quality and outcoupling efficiency due to the subwavelength nature of the semiconductor ridge-waveguides typically used. In this thesis, a new technique is discussed for obtaining high power and good beam quality from THz QCLs, the THz quantum-cascade external cavity surface emitting laser (QC-VECSEL). The concept of the QC-VECSEL is to use THz QC-gain material to design a millimeter-scale reflective amplifying surface, or metasurface, for free space THz waves and incorporate it into a free-space THz resonant cavity to provide feedback to the amplification and form a laser. In this manner, the beam shape is determined by the external cavity, which supports fundamental Gaussian solutions. Further, the metasurface itself is composed of a subwavelength array (to prevent diffraction) of surface-coupled QC-elements whose properties, such as phase and polarization response, can be engineered on a unit cell basis allowing for a variety of unique experiments. The power output power of the QC-VECSEL can be scaled by either increasing the size of the metasurface, or increasing the density (or fill factor) of QC-elements across the surface. In this work, large area metasurfaces with high fill-factor have been studied and demonstrated up to 1.35 W of peak output power for a QC-VECSEL operating at 3.4 THz at a heat sink temperature of 4 K. A peak wall-plug efficiency of ~2% is demonstrated, but observation of self lasing from the metasurface at high bias (when no external cavity is provided) in combination with a simultaneous roll-off in VECSEL output power suggests even higher efficiency can be achieved with improved suppression of self-lasing modes. The output beam is well fit to a Gaussian distribution with a 4 degree full-width half-maximum divergence angle. In addition to power and beam quality, the QC-VECSEL opens the door to many interesting and unique studies via engineering of the metasurface properties and external cavity. Much of this thesis describes frequency tuning of QC-VECSELs based on broadband metasurfaces by varying the length of the external cavity. By making the external cavity extremely short (comparable to the operating wavelength), we are able to push all other external cavity modes outside of the gain bandwidth of the metasurface and demonstrate more than 20% fractional single-mode tuning around a center operating frequency of 3.5 THz. Because there are almost no diffraction losses at such a short cavity, the size of the metasurface could be reduced, allowing for continuous wave lasing with up to 20 milliwatts of output power at a heatsink temperature of 77 K, though the output power is highly variable as the reflectance of the output coupler has a strong frequency dependence. At the time of writing this, these are record performances in both frequency tuning and high-temperature continuous wave operation for lasers based on THz QC-gain material. The amount of tuning that be achieved with this approach is limited by the phase response of the metasurface, which squeezes the external cavity modes closer together in the spectral domain. Development of metasurfaces with lower electrical power consumption and higher conversion efficiency for the purpose of improving continuous wave performance. A sparse, patch-based metasurface with reduced power consumption is demonstrated, though the design was not optimal and only showed a 20% reduction in current draw compared to the previously demonstrated metasurfaces. Routes towards improving the performance are discussed. The last subject discussed is the design of a mid-infrared (IR) QC-VECSEL. Due to the large metal losses at mid-IR frequencies compared to THz, the technique used to develop THz QC-VECSELs cannot be directly extended to the mid-IR. We propose a scheme based on a diffraction grating to provide surface coupling of the QC-gain material. Progress on experimental realization is discussed, but lasing has not yet been observed.

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 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.