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Author: Matthew Michael Suttinger
Publisher:
ISBN:
Category :
Languages : en
Pages : 47
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Book Description
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.
Author: Matthew Michael Suttinger
Publisher:
ISBN:
Category :
Languages : en
Pages : 47
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Book Description
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.
Author: Chao Xu
Publisher:
ISBN:
Category : Lasers
Languages : en
Pages : 128
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Book Description
Recent advances in Terahertz Quantum Cascade Laser (THz QCL) development are pushing this technology ever closer to practical application, particularly within the spectroscopic field. For this reason, optimizing the operation of THz QCL frequency combs, which can potentially provide unprecedented accuracy and stability to the optical spectra in a broad frequency band, is of particular interest to the research community. The THz QCLs frequency comb was only recently realized using two separate techniques: either a broad-gain active region or a group velocity dispersion controlled waveguide. However, due to residual optical dispersion from both the gain medium and the cold waveguide, comb formation in these reported THz QCLs can only sustain a limited current injection region and the observed comb frequency range is much narrower than the bandwidth of the designed gain medium. To overcome these limitations, this thesis targets a new THz QCL frequency comb device design that simultaneously exploits the broadband gain active region and a group velocity dispersion (GVD)-compensated waveguide over an octave frequency band of 2-4 THz. In designing a broadband gain active region, two heterogeneous structures are proposed and simulated, with one combining three different bound-to-continuum (BTC) active regions operating at a temperature of 25 K, and another one consisting of four different resonant-phonon (RP) active regions operating at the liquid nitrogen temperature (77 K) or higher. The simulation results show that both active region designs can provide a broadband and 'flat-top' gain profile covering the frequency range from 2 to 4 THz. To design a group velocity dispersion-compensated waveguide, strategies are explored for simulating chirped Distributed Bragg Reflectors (DBRs) that can serve as THz QCL metal-metal waveguides, and one-dimensional (1D) and three-dimensional (3D) modeling approaches are established and verified. A novel two-section chirped DBR is proposed, which provides substantially-improved group delay compensation over a broadband octave frequency range from 2 to 4 THz. Two THz QCL structures are grown using in-house molecular beam epitaxy and THz QCL devices equipped with a metal-metal waveguides are fabricated in the University of Waterloo Quantum-Nano-Centre clean-room fabrication lab. The experimental results demonstrate that the new THz QCL active region design can operate up to a maximum lasing temperature of 111 K, and with a broad lasing spectrum covering frequencies from 2.36 to 2.86 THz under pulse mode, at temperature of 13 K. The combined theoretical and experimental work would ultimately lead to the demonstration of improved THz QCL frequency comb operation over the broadband range from 2 to 4 THz.
Author: Tasmim Alam
Publisher: Cuvillier Verlag
ISBN: 3736962975
Category : Science
Languages : en
Pages : 132
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Book Description
Quantum cascade lasers (QCLs) are attractive for high-resolution spectroscopy because they can provide high power and a narrow linewidth. They are particularly promising in the terahertz (THz) range since they can be used as local oscillators for heterodyne detection as well as transmitters for direct detection. However, THz QCL-based technologies are still under development and are limited by the lack of frequency tunability as well as the frequency and output power stability for free-running operation. In this dissertation, frequency tuning and linewidth of THz QCLs are studied in detail by using rotational spectroscopic features of molecular species. In molecular spectroscopy, the Doppler eff ect broadens the spectral lines of molecules in the gas phase at thermal equilibrium. Saturated absorption spectroscopy has been performed that allows for sub-Doppler resolution of the spectral features. One possible application is QCL frequency stabilization based on the Lamb dip. Since the tunability of the emission frequency is an essential requirement to use THz QCL for high-resolution spectroscopy, a new method has been developed that relies on near-infrared (NIR) optical excitation of the QCL rear-facet. A wide tuning range has been achieved by using this approach. The scheme is straightforward to implement, and the approach can be readily applied to a large class of THz QCLs. The frequency and output stability of the local oscillator has a direct impact on the performance and consistency of the heterodyne spectroscopy. A technique has been developed for a simultaneous stabilization of the frequency and output power by taking advantage of the frequency and power regulation by NIR excitation. The results presented in this thesis will enable the routine use of THz QCLs for spectroscopic applications in the near future.
Author: Dan Botez
Publisher: Cambridge University Press
ISBN: 1108570607
Category : Technology & Engineering
Languages : en
Pages : 552
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Book Description
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.
Author: Jérôme Faist
Publisher: Oxford University Press
ISBN: 0198528248
Category : Science
Languages : en
Pages : 321
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Book Description
This book describes the physics, fabrication technology, and applications of the quantum cascade laser.
Author: Christopher Andrew Sigler
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Scaling the continuous-wave (CW) power of quantum cascade lasers (QCLs) beyond ~5 W has proven difficult, and beam-quality degradation is common when scaling the device volume for high power. The primary objective of this work was to develop methods for spatially-coherent power scaling of mid-infrared-emitting QCLs to high CW powers. Two approaches were investigated: 1) resonant leaky-wave-coupled antiguided phase-locked laser arrays; and 2) grating-coupled surface-emitting lasers (GCSELs). These two approaches can be combined to realize high surface-emitted powers in a spatially and temporally coherent beam pattern. Optical and thermal models of planarized leaky-wave-coupled phase-locked QCL arrays were coupled together to investigate the influence of thermal lensing on modal behavior. Self-focusing under thermally-induced index variations across the array were found to impact the field profile and promote multi-moding due to gain spatial hole burning. Two techniques were found to mitigate this effect: 1) employing anti-resonant reflective-optical waveguide terminations outside the array; and 2) chirping the element width across the array to obtain identical optically-equivalent widths under CW operation, eliminating thermal lensing at a particular operating condition. Five-element phase-locked arrays of 4.7 μm-emitting QCLs were demonstrated which operate in a near-diffraction-limited beam (primarily in the in-phase array mode) to 5.1 W peak pulsed power, in agreement with simulations. Spectrally resolved near- and far-field measurements indicate that the wide spectral bandwidth of the QCL core promotes multi-mode operation at high drive levels. An optimized array design was identified to allow sole in-phase mode operation to high drive levels above threshold, indicating that full spatial coherence to high output powers does not require full temporal coherence for phase-locked laser arrays. Lastly, a novel method for obtaining a single-lobed beam pattern from transverse magnetic (TM)-polarized GCSELs is proposed: resonant coupling of the optical mode of a QCL to the antisymmetric surface plasmon mode of a 2nd-order distributed feedback metal/semiconductor grating results in strong antisymmetric-mode absorption. Lasing in the symmetric mode, resulting in a single-lobed far-field beam pattern from the substrate emission, is strongly favored around resonance. For infinite-length devices, the symmetric mode has negligible absorption loss while still being efficiently outcoupled by the grating.
Author: Alfredo Bismuto
Publisher: LAP Lambert Academic Publishing
ISBN: 9783846588376
Category :
Languages : en
Pages : 208
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Book Description
This work describes the work performed by the author at the ETH Zurich, under the supervision of Prof. Jerome Faist on the optimization of high performance quantum cascade lasers (QCLs) in the Mid-IR spectral region. The main factors influencing laser performance have therefore been analyzed. In particular the optimization of the laser design in order to improve the electron tranport and the optical gain. In addition a detailed analysis of the fabrication process is performed and a novel process scheme is presented for buried heterostructure lasers.
Author: Peter W. Epperlein
Publisher: John Wiley & Sons
ISBN: 1118481860
Category : Technology & Engineering
Languages : en
Pages : 522
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Book Description
This reference book provides a fully integrated novel approach to the development of high-power, single-transverse mode, edge-emitting diode lasers by addressing the complementary topics of device engineering, reliability engineering and device diagnostics in the same book, and thus closes the gap in the current book literature. Diode laser fundamentals are discussed, followed by an elaborate discussion of problem-oriented design guidelines and techniques, and by a systematic treatment of the origins of laser degradation and a thorough exploration of the engineering means to enhance the optical strength of the laser. Stability criteria of critical laser characteristics and key laser robustness factors are discussed along with clear design considerations in the context of reliability engineering approaches and models, and typical programs for reliability tests and laser product qualifications. Novel, advanced diagnostic methods are reviewed to discuss, for the first time in detail in book literature, performance- and reliability-impacting factors such as temperature, stress and material instabilities. Further key features include: practical design guidelines that consider also reliability related effects, key laser robustness factors, basic laser fabrication and packaging issues; detailed discussion of diagnostic investigations of diode lasers, the fundamentals of the applied approaches and techniques, many of them pioneered by the author to be fit-for-purpose and novel in the application; systematic insight into laser degradation modes such as catastrophic optical damage, and a wide range of technologies to increase the optical strength of diode lasers; coverage of basic concepts and techniques of laser reliability engineering with details on a standard commercial high power laser reliability test program. Semiconductor Laser Engineering, Reliability and Diagnostics reflects the extensive expertise of the author in the diode laser field both as a top scientific researcher as well as a key developer of high-power highly reliable devices. With invaluable practical advice, this new reference book is suited to practising researchers in diode laser technologies, and to postgraduate engineering students.
Author: Wolfgang Jantsch
Publisher: American Institute of Physics
ISBN:
Category : Science
Languages : en
Pages : 774
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Book Description
This book features peer-reviewed papers that were presented at the 28th International Conference on the Physics of Semiconductors. This biannual conference presents and discusses all important developments and outstanding recent results in the field of semiconductor physics: one of the most important disciplines in solid state physics. Semiconductor physics provides the scientific basis for the microelectronic device industry.
Author: Ayushi Rajeev
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
When using conventional substrates, such as InP and GaAs, the materials constituting the superlattice (SL) core region of the quantum cascade laser (QCL) are constrained by strain-induced critical-thickness limitations. Metamorphic buffer layers (MBLs) can serve as "virtual substrates" with a designer-chosen surface lattice constant, thus expanding the compositional-design space for a variety of device structures, including short-wavelength QCLs. An optimized short-wavelength (3.4 [mu]m) single-phonon-resonant (SPR)+ miniband extraction QCL design, grown on an [InxGa1-xAs] MBL, is presented along with the optical and thermal device considerations in play. MBLs can be grown with a variety of graded regions such as linear composition grade from GaAs to [InxGa1-xAs] or by employing dislocation filters between Si substrate and InP. QCL and test superlattices' regrowth on these MBLs with the corresponding materials and device analysis, is presented in this work. In addition to the materials limitation for the design of QCL devices, the requirement to have the constituent layers (1-5 nm) to be precisely controlled in the various compositions and thicknesses, is a challenge. Interfacial grading in strained SLs is studied via atom probe tomography for SLs with various layer thicknesses and relative lattice strains. The tip reconstructions are analyzed by fitting the interfaces to diffusion profiles. Mechanisms possible for the observed interdiffusion profile, such as surface segregation and/or bulk diffusion, are discussed. With an understanding of the compositional gradient at the interfaces, together with optimized QCL designs and regrowth on the MBLs, short-wavelength QCLs with high performances can be achieved
