We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.
To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure [email protected]
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Terahertz quantum cascade laser sources based on intra-cavity difference frequency generation are currently the only electrically-pumped monolithic semiconductor light sources providing broadly-tunable terahertz output at frequencies up to 6 THz at room temperature. Relying on the active regions with the giant second-order nonlinear susceptibility and the Cherenkov phase matching scheme, these devices demonstrated drastic improvements in performance in the past several years and can now produce narrow-linewidth single-mode terahertz emission that is tunable from below 1 THz to almost 6 THz with power output sufficient for imaging and spectroscopic applications. This chapter provides a comprehensive overview of this device technology
This chapter reviews the applications of terahertz (THz) quantum cascade lasers (QCLs). THz QCLs have come a long way since their first demonstration in 2002. Although still operating at or close to cryogenic temperatures, their applications have been multiplying steadily over the last decade, helped by the availability of compact commercial THz QCL systems and the growing adoption of the THz QCL technology in the THz scientific community. Currently, the key fields of THz QCL applications are imaging, spectroscopy and sensing.
Laser feedback interferometry, based on the self-mixing (SM) effect in quantum cascade lasers (QCLs), is one of the simplest coherent techniques, for which the emission source can also play the role of a highly-sensitive detector. The combination of QCLs and SM is particularly attractive for sensing applications, notably in the THz band where it provides a high-speed high-sensitivity detection mechanism which inherently suppresses unwanted background radiation. The SM phenomenon in QCLs has been exploited for a wide range of applications, including the measurement of internal laser characteristics, two- and three-dimensional imaging, materials analysis and near-field imaging. This chapter provides an overview of the SM effect in QCLs, and reviews the state of the art in sensing using this technique.
High-power terahertz quantum-cascade lasers (QCLs) are desired for a variety of applications in imaging and spectroscopy. The best performance at practical operating temperatures for single-mode terahertz QCLs is realized with metallic cavities due to a strong plasmonic mode confinement of the optical mode within the cavity. However, such plasmonic lasers suffer from poor beam shapes, low output power, and multi-mode spectral behavior. Development of distributed-feedback (DFB) techniques to improve spectral as well as modal properties becomes indispensable for terahertz QCLs to address targeted applications that typically require single-mode operation, frequency stability and specificity, and optimal far-field beam quality with single-lobed profile and low angular divergence. This chapter describes the theory, design methodologies, and key results from a sampling of a wide variety of DFB techniques that have been implemented in literature for monolithic terahertz QCLs with metallic cavities in both edge-emitting and surface-emitting configurations, either of which have their specific application areas and advantages much-like that for infrared diode lasers.
This chapter reviews typical waveguide and active region designs for quantum cascade lasing in the terahertz (THz) frequency range. Operating principles are analyzed in details with special attention paid to the most recent developments with the state-of-the-art device performance. The maximum operation temperature of THz QCL is still the main obstacle for its wide employment in applications, although it has been lifted to 250 K, allowing cryogenic-free THz coherent radiation for potentially portable applications. Optimization of various limiting factors in the most advanced resonant-phonon designs or the combined designs with scattering-assisted injection scheme could be promising for further breakthroughs in achieving higher temperature operations. The discussions in this chapter mainly focus on the matured GaAs/AlGaAs material system, but the design strategies can be applied to THz QCLs utilizing other material systems, which may overcome the main challenges of the GaAs/AlGaAs material system and achieve better performance in the future.
Optical gas sensing is a promising alternative to analytical, electrochemical and semiconductor sensors that can offer fast responses times, minimal drift, high gas specificity, with zero cross-response to other gases. Quantum cascade lasers represent the optimal choice as mid-IR sources due to their high output power, compactness, narrow spectral linewidth and broad wavelength tunability. Among optical techniques, Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) has been demonstrated to be a leading-edge technology for real-world gas detection applications, thanks to its modularity, ruggedness, portability and real-time operation capability. QEPAS sensors typically achieve gas detection limits of few parts-per billion level. The basic principles of PAS are provided with a discussion on optoacoustic waves generation and detection. Quartz tuning forks physics is presented in detail, covering aspects like flexural modes resonance, including overtone, quality factor and microresonator tubes configuration. Finally, an overview of QCL-based QEPAS gas sensors for real-world applications, like environmental monitoring, breath sensing, leak detection and multi-gas detection is provided.
The advent of optical frequency combs revolutionized many research fields from metrology to high precision spectroscopy. It was recently demonstrated that broadband quantum cascade lasers can operate as frequency combs. As such, they operate under direct electrical pumping at both mid-infrared and terahertz frequencies, reaching powers in the watt range with multi-terahertz bandwidths. As their key application field, they unlock the advantages in speed and accuracy of the dual-comb spectroscopy technique in a frequency range where molecules have their fundamental vibrational and rotational bands. In this Chapter we review the design and basic functioning principles of these devices, the characterization of their coherence properties as well as few example applications.
Quantum cascade lasers are based on Intersubband transitions between quantum confined states in semiconductor heterostructures. The origin of these states is briefly described in this chapter starting with linear combination of atomic orbitals and then proceeding to the k.P theory. The relations between the interband and Intersubband transitions including their oscillator strength and selection rules are established. It is shown that “giant” Intersubband dipole owes its existence to the confinement induced band mixing. Aside from the radiative Intersubband transitions investigated in this chapter, nonradiative transitions also play important roles in QCL operation, hence most relevant of these processes: electron phonon, electron-electron, interface roughness and alloy disorder are also described in detail.
This chapter provides an overview of a class terahertz quantum cascade lasers based upon amplifying electromagnetic metasurfaces. The metasurface comprises two-dimensional arrays of sub-wavelength surface radiating antenna elements, in which the antennas are loaded with the quantum cascade laser gain material. Several types devices are described: (a) vertical-external-cavity surface-emitting-lasers (VECSELs) in which the amplifying metasurface is paired with external optics to form a laser cavity; (b) monolithic metasurface lasers in which the metasurface array self-oscillates in a coherent supermode; and (c) metasurfaces which operate below threshold as free-space terahertz amplifiers. The metasurface approach allows the realization of large-area radiating apertures while preserving the sub-wavelength sized of the individual metallic waveguide antenna elements. This has resulted in significantly improved performance and functionality in many categories, including lasers with high-quality beam patterns, high-efficiency lasers with scalable output powers, broadband spectral tunability of single-mode emission, and free-space amplification of terahertz beams.
Quantum cascade lasers (QCLs) emitting in the 4-10 micron wavelength range are treated with emphasis on key issues not covered in previous books on QCLs. The foremost issue discussed: what does it take to achieve continuous-wave (CW) operation to multi-watt powers in a highly efficient manner, is of interest to a wide range of applications. A comprehensive review of the temperature dependence of the electro-optical characteristics of QCLs is presented by including elastic scattering and carrier-leakage triggered by elastic and inelastic scattering, thus accounting for all mechanisms behind the device internal efficiency. Maximizing the CW wall-plug efficiency via conduction-band and elastic-scattering engineering, and photon-induced carrier transport is treated in detail. Then coherent-power scaling is discussed for both one- and two-dimensional (2-D) structures with emphasis on the optimal solution: high-index-contrast (HC) photonic-crystal (PC) lasers. Grating-coupled surface-emitting lasers are also treated with emphasis on those needed for 2-D HC-PC lasers; that is, devices most likely to operate in diffraction-limited, single-lobe beam pattern to multi-watt CW output powers
Laser spectroscopy in the mid-infrared (IR) and terahertz (THz) spectral regions is of particular interest since it gives access to the fundamental rovibrational bands of many molecules as well as to molecular rotational bands and lattice vibrations in solid-state samples. Among all modern laser technologies, optical frequency combs have emerged as the most promising sources for high-resolution spectrometers with broadband spectral coverage. We provide an overview of recent advancements in electrically pumped quantum- and interband-cascade-laser (QCL and ICL) frequency combs operating in the mid-IR and THz regions as an important step towards field applications with truly integrated and scalable frequency-comb technology. We also discuss dual-comb spectroscopy techniques that offers fast chemical sensing without the need for optomechanical tuning or dispersive spectrometers, and provide an overview of the spectroscopic capabilities provided by QCL and ICL dual-comb spectrometers. Measurement approaches and recent experimental implementations of mid-IR and THz dual-comb spectroscopy of chemicals by various research groups using QCL and ICL frequency-comb technology are discussed
The chapter reviews long wavelength mid-infrared quantum cascade lasers (QCLs) emitting between 15 and 28 μm. Historically, 15 μm was a border wavelength above which the QCL performances dramatically degraded, which was partly due to an increase in optical losses in the devices with approaching the Reststrahlen band. This intrinsic limitation caused by multi-phonon absorption sets forbidden or favorable spectral areas depending on the employed materials. The chapter considers specific properties of long wavelength mid-infrared QCLs based on different materials, as well as more general issues related to the QCL design in this long-wavelength frontier of the mid-infrared. The discussed results are presented in the chronological order for each QCL material system, which allows the reader to follow the advances in the field.
Discover how mid-infrared and terahertz photonics has been revolutionized in this comprehensive overview of state-of-the art quantum cascade lasers (QCLs). Combining real-world examples with expert guidance, it provides a thorough treatment of practical applications, including high-power continuous-wave QCLs, frequency-comb devices, quantum-electronic transport and thermal transport modeling, and beam shaping in QCLs. With a focus on recent developments, such as frequency noise and frequency stabilization of QCLs, grating-outcoupled surface-emitting mid-infrared QCLs, coherent-power scaling of mid-IR and THz QCLs, metasurface-based surface-emitting THz QCLs, self-mixing in QCLs, and THz QCL sources based on difference-frequency generation, it also features detailed theoretical explanations of means for efficiency maximization, design criteria for high-power continuous-wave operation of QCLs, and QCL thermal modeling, enabling you to improve performance of current and future devices. Paving the way for new applications and further advancements, this is an invaluable resource for academics, researchers, and practitioners in electrical, opto-electronic, and photonic engineering.
Chapter devoted to the basic quantum properties of entanglement and separability. Introduces the Schmidt decomposition for pure states and the positive partial transpose criterion for mixed states as entanglement witnesses. Introduces the famous Einstein–Podolsky–Rosen paradox and its implementation in terms of qubits, then the Bell inequality, quickly reviewing the experimental demonstrations that quantum mechanics violates this inequality. Gives examples of the use of entanglement in a quantum algorithm to accelerate an information task, namely a database search (Grover algorithm) and the possibility of teleportation of a quantum state.