Special Issue "Quantum Cascade Lasers - Advances and New Applications"

A special issue of Photonics (ISSN 2304-6732).

Deadline for manuscript submissions: closed (31 May 2016)

Special Issue Editor

Guest Editor
Prof. Dr. Manijeh Razeghi

Center for Quantum Devices, Department of Electrical Engineering and Computer Science, Northwestern University, Evanston, IL 60208-312, USA
Website | E-Mail
Interests: quantum devices operating in the deep ultraviolet spectral band; quantum dots; quantum cascade

Special Issue Information

Dear Colleagues,

Certain technologies are enabling. Fiber optics and telecommunication would never have become widespread without compact, inexpensive, and reliable laser diodes and photodetectors, made from InP-based semiconductors. A similar application revolution at longer wavelengths (2 < λ < 300 μm) is underway, thanks to advances in a number of different semiconductor technologies. This spectral region can be used to identify almost any chemical based on structural resonance. This is valuable for everything from medical diagnostics, homeland security, industrial quality control, and even pollution monitoring.

Long wavelength infrared lasers, which used to require cryogenic cooling, are now being developed for high power and high efficiency at room temperature and above. Additional functionality is also being realized, including electrical tuning, surface emission, frequency combs, and photonic integrated circuits. All of these technologies are constantly evolving, and this Special Issue is designed to give a current overview of the state-of-the-art for cascade lasers and applications in the 2–300 μm wavelength range.

Prof. Dr. Manijeh Razeghi
Guest Editor

Manuscript Submission Information

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Keywords

  • Theory and design of quantum cascade lasers
  • New breakthroughs in quantum cascade laser performance
  • Novel material systems for improved performance
  • Nonlinear effects in quantum cascade lasers
  • Broadband gain media design and growth
  • Quantum cascade laser photonic integrated circuits
  • Power scaling of cascade lasers
  • Low cost laser manufacturing techniques
  • Chemical/biomedical applications for cascade lasers
  • Communication applications for cascade lasers
  • Active imaging applications for cascade lasers
  • Defense/homeland security applications for cascade lasers

Published Papers (21 papers)

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Research

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Open AccessArticle Frequency Tuning and Modulation of a Quantum Cascade Laser with an Integrated Resistive Heater
Received: 23 June 2016 / Revised: 25 July 2016 / Accepted: 26 July 2016 / Published: 30 July 2016
Cited by 4 | PDF Full-text (3508 KB) | HTML Full-text | XML Full-text
Abstract
We present a detailed experimental investigation of the use of a novel actuator for frequency tuning and modulation in a quantum cascade laser (QCL) based on a resistive integrated heater (IH) placed close to the active region. This new actuator is attractive for [...] Read more.
We present a detailed experimental investigation of the use of a novel actuator for frequency tuning and modulation in a quantum cascade laser (QCL) based on a resistive integrated heater (IH) placed close to the active region. This new actuator is attractive for molecular spectroscopy applications as it enables fast tuning of the QCL wavelength with a minor influence on the optical output power, and is electrically-controlled. Using a spectroscopic setup comprising a low-pressure gas cell, we measured the tuning and modulation properties of a QCL emitting at 7.8 μm as a function of the active region and IH currents. We show that a current step applied to the IH enables the laser frequency to be switched by 500 MHz in a few milliseconds, as fast as for a step of the current in the active region, and limited by heat dissipation towards the laser sub-mount. The QCL optical frequency can be modulated up to ~100 kHz with the IH current, which is one order of magnitude slower than for the QCL current, but sufficient for many spectroscopic applications. We discuss the experimental results using a thermal model of the heat transfer in terms of cascaded low-pass filters and extract the respective cut-off frequencies. Finally, we present a proof-of-principle experiment of wavelength modulation spectroscopy of a N2O transition performed with a modulation of the IH current and show some potential benefits in comparison to QCL current modulation, which results from the reduced associated amplitude modulation. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Development of a Multi-Objective Evolutionary Algorithm for Strain-Enhanced Quantum Cascade Lasers
Received: 1 June 2016 / Revised: 16 July 2016 / Accepted: 18 July 2016 / Published: 22 July 2016
Cited by 1 | PDF Full-text (524 KB) | HTML Full-text | XML Full-text
Abstract
An automated design approach using an evolutionary algorithm for the development of quantum cascade lasers (QCLs) is presented. Our algorithmic approach merges computational intelligence techniques with the physics of device structures, representing a design methodology that reduces experimental effort and costs. The algorithm [...] Read more.
An automated design approach using an evolutionary algorithm for the development of quantum cascade lasers (QCLs) is presented. Our algorithmic approach merges computational intelligence techniques with the physics of device structures, representing a design methodology that reduces experimental effort and costs. The algorithm was developed to produce QCLs with a three-well, diagonal-transition active region and a five-well injector region. Specifically, we applied this technique to Al x Ga 1 - x As/In y Ga 1 - y As strained active region designs. The algorithmic approach is a non-dominated sorting method using four aggregate objectives: target wavelength, population inversion via longitudinal-optical (LO) phonon extraction, injector level coupling, and an optical gain metric. Analysis indicates that the most plausible device candidates are a result of the optical gain metric and a total aggregate of all objectives. However, design limitations exist in many of the resulting candidates, indicating need for additional objective criteria and parameter limits to improve the application of this and other evolutionary algorithm methods. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Engineering Multi-Section Quantum Cascade Lasers for Broadband Tuning
Received: 1 June 2016 / Revised: 17 June 2016 / Accepted: 17 June 2016 / Published: 27 June 2016
Cited by 3 | PDF Full-text (1730 KB) | HTML Full-text | XML Full-text
Abstract
In an effort to overcome current limitations to electrical tuning of quantum cascade lasers, a strategy is proposed which combines heterogeneous quantum cascade laser gain engineering with sampled grating architectures. This approach seeks to not only widen the accessible spectral range for an [...] Read more.
In an effort to overcome current limitations to electrical tuning of quantum cascade lasers, a strategy is proposed which combines heterogeneous quantum cascade laser gain engineering with sampled grating architectures. This approach seeks to not only widen the accessible spectral range for an individual emitter, but also compensate for functional non-uniformity of reflectivity and gain lineshapes. A trial laser with a dual wavelength core is presented which exhibits electroluminescence over a 750 cm−1 range and discrete single mode laser emission over a 700 cm−1 range. Electrical tuning over 180 cm−1 is demonstrated with a simple sampled grating design. A path forward to even wider tuning is also described using more sophisticated gain and grating design principles. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Quantum Transport Simulation of High-Power 4.6-μm Quantum Cascade Lasers
Received: 4 May 2016 / Revised: 5 June 2016 / Accepted: 7 June 2016 / Published: 10 June 2016
Cited by 4 | PDF Full-text (640 KB) | HTML Full-text | XML Full-text
Abstract
We present a quantum transport simulation of a 4.6-μm quantum cascade laser (QCL) operating at high power near room temperature. The simulation is based on a rigorous density-matrix-based formalism, in which the evolution of the single-electron density matrix follows a Markovian [...] Read more.
We present a quantum transport simulation of a 4.6- μ m quantum cascade laser (QCL) operating at high power near room temperature. The simulation is based on a rigorous density-matrix-based formalism, in which the evolution of the single-electron density matrix follows a Markovian master equation in the presence of applied electric field and relevant scattering mechanisms. We show that it is important to allow for both position-dependent effective mass and for effective lowering of very thin barriers in order to obtain the band structure and the current-field characteristics comparable to experiment. Our calculations agree well with experiments over a wide range of temperatures. We predict a room-temperature threshold field of 62 . 5 kV/cm and a characteristic temperature for threshold-current-density variation of T 0 = 199 K . We also calculate electronic in-plane distributions, which are far from thermal, and show that subband electron temperatures can be hundreds to thousands of degrees higher than the heat sink. Finally, we emphasize the role of coherent tunneling current by looking at the size of coherences, the off-diagonal elements of the density matrix. At the design lasing field, efficient injection manifests itself in a large injector/upper lasing level coherence, which underscores the insufficiency of semiclassical techniques to address injection in QCLs. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Heterogeneously Integrated Distributed Feedback Quantum Cascade Lasers on Silicon
Received: 28 April 2016 / Revised: 29 May 2016 / Accepted: 30 May 2016 / Published: 2 June 2016
Cited by 15 | PDF Full-text (4476 KB) | HTML Full-text | XML Full-text
Abstract
Silicon integration of mid-infrared (MIR) photonic devices promises to enable low-cost, compact sensing and detection capabilities that are compatible with existing silicon photonic and silicon electronic technologies. Heterogeneous integration by bonding III-V wafers to silicon waveguides has been employed previously to build integrated [...] Read more.
Silicon integration of mid-infrared (MIR) photonic devices promises to enable low-cost, compact sensing and detection capabilities that are compatible with existing silicon photonic and silicon electronic technologies. Heterogeneous integration by bonding III-V wafers to silicon waveguides has been employed previously to build integrated diode lasers for wavelengths from 1310 to 2010 nm. Recently, Fabry-Pérot Quantum Cascade Lasers integrated on silicon provided a 4800 nm light source for mid-infrared (MIR) silicon photonic applications. Distributed feedback (DFB) lasers are appealing for many high-sensitivity chemical spectroscopic sensing applications that require a single frequency, narrow-linewidth MIR source. While heterogeneously integrated 1550 nm DFB lasers have been demonstrated by introducing a shallow surface grating on a silicon waveguide within the active region, no mid-infrared DFB laser on silicon has been reported to date. Here we demonstrate quantum cascade DFB lasers heterogeneously integrated with silicon-on-nitride-on-insulator (SONOI) waveguides. These lasers emit over 200 mW of pulsed power at room temperature and operate up to 100 °C. Although the output is not single mode, the DFB grating nonetheless imposes wavelength selectivity with 22 nm of thermal tuning. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Rapid and Sensitive Quantification of Isotopic Mixtures Using a Rapidly-Swept External Cavity Quantum Cascade Laser
Received: 31 March 2016 / Revised: 16 May 2016 / Accepted: 17 May 2016 / Published: 23 May 2016
Cited by 6 | PDF Full-text (3944 KB) | HTML Full-text | XML Full-text
Abstract
A rapidly-swept external-cavity quantum cascade laser with an open-path Herriott cell is used to quantify gas-phase chemical mixtures of D2O and HDO at a rate of 40 Hz (25-ms measurement time). The chemical mixtures were generated by evaporating D2O [...] Read more.
A rapidly-swept external-cavity quantum cascade laser with an open-path Herriott cell is used to quantify gas-phase chemical mixtures of D2O and HDO at a rate of 40 Hz (25-ms measurement time). The chemical mixtures were generated by evaporating D2O liquid near the open-path Herriott cell, allowing the H/D exchange reaction with ambient H2O to produce HDO. Fluctuations in the ratio of D2O and HDO on timescales of <1 s due to the combined effects of plume transport and the H/D exchange chemical reaction are observed. Noise-equivalent concentrations (1σ) (NEC) of 147.0 ppbv and 151.6 ppbv in a 25-ms measurement time are determined for D2O and HDO, respectively, with a 127-m optical path. These NECs are improved to 23.0 and 24.0 ppbv with a 1-s averaging time for D2O and HDO, respectively. NECs <200 ppbv are also estimated for N2O, 1,1,1,2–tetrafluoroethane (F134A), CH4, acetone and SO2 for a 25-ms measurement time. The isotopic precision for measurement of the [D2O]/[HDO] concentration ratio of 33‰ and 5‰ is calculated for the current experimental conditions for measurement times of 25 ms and 1 s, respectively. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessCommunication Multimode, Aperiodic Terahertz Surface-Emitting Laser Resonators
Received: 5 April 2016 / Revised: 13 May 2016 / Accepted: 16 May 2016 / Published: 20 May 2016
Cited by 1 | PDF Full-text (6327 KB) | HTML Full-text | XML Full-text
Abstract
Quasi-crystal structures are conventionally built following deterministic generation rules although they do not present a full spatial periodicity. If used as laser resonators, they open up intriguing design possibilities that are simply not possible in conventional periodic photonic crystals: the distinction between symmetric [...] Read more.
Quasi-crystal structures are conventionally built following deterministic generation rules although they do not present a full spatial periodicity. If used as laser resonators, they open up intriguing design possibilities that are simply not possible in conventional periodic photonic crystals: the distinction between symmetric (vertically radiative but low quality factor Q) and anti-symmetric (non-radiative, high Q) modes is indeed here fully overcome, offering a concrete perspective of highly efficient vertical emitting resonators. We here exploit electrically pumped terahertz quantum cascade heterostructures to devise two-dimensional seven-fold quasi-crystal resonators, exploiting rotational order or irregularly distributed defects. By lithographically tuning the lattice quasi-periodicity and/or the hole radius of the imprinted patterns, efficient multimode surface emission with a rich sequence of spectral lines distributed over a 2.9–3.4 THz bandwidth was reached. We demonstrated multicolor emission with 67 mW of peak optical power, slope efficiencies up to ≈70 mW/A, 0.14% wall plug efficiencies and beam profile results of the rich quasi-crystal Fourier spectrum that, in the case of larger rotational order, can reach very low divergence. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Liver Status Assessment by Spectrally and Time Resolved IR Detection of Drug Induced Breath Gas Changes
Received: 31 March 2016 / Revised: 28 April 2016 / Accepted: 30 April 2016 / Published: 20 May 2016
Cited by 3 | PDF Full-text (2320 KB) | HTML Full-text | XML Full-text
Abstract
The actual metabolic capacity of the liver is crucial for disease identification, liver therapy, and liver tumor resection. By combining induced drug metabolism and high sensitivity IR spectroscopy of exhaled air, we provide a method for quantitative liver assessment at bedside within 20 [...] Read more.
The actual metabolic capacity of the liver is crucial for disease identification, liver therapy, and liver tumor resection. By combining induced drug metabolism and high sensitivity IR spectroscopy of exhaled air, we provide a method for quantitative liver assessment at bedside within 20 to 60 min. Fast administration of 13C-labelled methacetin induces a fast response of liver metabolism and is tracked in real-time by the increase of 13CO2 in exhaled air. The 13CO2 concentration increase in exhaled air allows the determination of the metabolic liver capacity (LiMAx-test). Fluctuations in CO2 concentration, pressure and temperature are minimized by special gas handling, and tracking of several spectrally resolved CO2 absorption bands with a quantum cascade laser. Absorption measurement of different 12CO2 and 13CO2 rotation-vibration transitions in the same time window allows for multiple referencing and reduction of systematic errors. This FLIP (Fast liver investigation package) setup is being successfully used to plan operations and determine the liver status of patients. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Modeling the Electro-Optical Performance of High Power Mid-Infrared Quantum Cascade Lasers
Received: 24 March 2016 / Revised: 10 May 2016 / Accepted: 10 May 2016 / Published: 17 May 2016
Cited by 2 | PDF Full-text (4898 KB) | HTML Full-text | XML Full-text
Abstract
Performance modeling of the characteristics of mid-infrared quantum cascade lasers (MIR QCL) is an essential element in formulating consistent component requirements and specifications, in preparing guidelines for the design and manufacture of the QCL structures, and in assessing different modes of operation of [...] Read more.
Performance modeling of the characteristics of mid-infrared quantum cascade lasers (MIR QCL) is an essential element in formulating consistent component requirements and specifications, in preparing guidelines for the design and manufacture of the QCL structures, and in assessing different modes of operation of the laser device. We use principles of system physics to analyze the electro-optical characteristics of high power MIR QCL, including thermal backfilling of the lower laser level, hot electron effects, and Stark detuning during lasing. The analysis is based on analytical modeling to give simple mathematical expressions which are easily incorporated in system-level simulations of defense applications such as directed infrared countermeasures (DIRCM). The paper delineates the system physics of the electro-optical energy conversion in QCL and the related modeling. The application of the performance model to a DIRCM QCL is explained by an example. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Mid-Infrared Quantum-Dot Quantum Cascade Laser: A Theoretical Feasibility Study
Received: 31 March 2016 / Revised: 6 May 2016 / Accepted: 9 May 2016 / Published: 13 May 2016
Cited by 1 | PDF Full-text (465 KB) | HTML Full-text | XML Full-text
Abstract
In the framework of a microscopic model for intersubband gain from electrically pumped quantum-dot structures we investigate electrically pumped quantum-dots as active material for a mid-infrared quantum cascade laser. Our previous calculations have indicated that these structures could operate with reduced threshold current [...] Read more.
In the framework of a microscopic model for intersubband gain from electrically pumped quantum-dot structures we investigate electrically pumped quantum-dots as active material for a mid-infrared quantum cascade laser. Our previous calculations have indicated that these structures could operate with reduced threshold current densities while also achieving a modal gain comparable to that of quantum well active materials. Here, we study the influence of two important quantum-dot material parameters, namely inhomogeneous broadening and quantum-dot sheet density, on the performance of a proposed quantum cascade laser design. In terms of achieving a positive modal net gain, a high quantum-dot density can compensate for moderately high inhomogeneous broadening, but at a cost of increased threshold current density. However, by minimizing quantum-dot density with presently achievable inhomogeneous broadening and total losses, significantly lower threshold densities than those reported in quantum-well quantum-cascade lasers are predicted by our theory. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Recent Advances and Applications of External Cavity-QCLs towards Hyperspectral Imaging for Standoff Detection and Real-Time Spectroscopic Sensing of Chemicals
Received: 31 March 2016 / Revised: 27 April 2016 / Accepted: 30 April 2016 / Published: 13 May 2016
Cited by 20 | PDF Full-text (5798 KB) | HTML Full-text | XML Full-text
Abstract
External-cavity quantum cascade lasers (EC-QCL) are now established as versatile wavelength-tunable light sources for analytical spectroscopy in the mid-infrared (MIR) spectral range. We report on the realization of rapid broadband spectral tuning with kHz scan rates by combining a QCL chip with a [...] Read more.
External-cavity quantum cascade lasers (EC-QCL) are now established as versatile wavelength-tunable light sources for analytical spectroscopy in the mid-infrared (MIR) spectral range. We report on the realization of rapid broadband spectral tuning with kHz scan rates by combining a QCL chip with a broad gain spectrum and a resonantly driven micro-opto-electro-mechanical (MOEMS) scanner with an integrated diffraction grating in Littrow configuration. The capability for real-time spectroscopic sensing based on MOEMS EC-QCLs is demonstrated by transmission measurements performed on polystyrene reference absorber sheets, as well as on hazardous substances, such as explosives. Furthermore, different applications for the EC-QCL technology in spectroscopic sensing are presented. These include the fields of process analysis with on- or even inline capability and imaging backscattering spectroscopy for contactless identification of solid and liquid contaminations on surfaces. Recent progress in trace detection of explosives and related precursors in relevant environments as well as advances in food quality monitoring by discriminating fresh and mold contaminated peanuts based on their MIR backscattering spectrum is shown. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Cascade Type-I Quantum Well GaSb-Based Diode Lasers
Received: 7 April 2016 / Revised: 2 May 2016 / Accepted: 4 May 2016 / Published: 11 May 2016
Cited by 7 | PDF Full-text (1927 KB) | HTML Full-text | XML Full-text
Abstract
Cascade pumping of type-I quantum well gain sections was utilized to increase output power and efficiency of GaSb-based diode lasers operating in a spectral region from 1.9 to 3.3 μm. Carrier recycling between quantum well gain stages was realized using band-to-band tunneling in [...] Read more.
Cascade pumping of type-I quantum well gain sections was utilized to increase output power and efficiency of GaSb-based diode lasers operating in a spectral region from 1.9 to 3.3 μm. Carrier recycling between quantum well gain stages was realized using band-to-band tunneling in GaSb/AlSb/InAs heterostructure complemented with optimized electron and hole injector regions. Coated devices with an ~100-μm-wide aperture and a 3-mm-long cavity demonstrated continuous wave (CW) output power of 1.96 W near 2 μm, 980 mW near 3 μm, 500 mW near 3.18 μm, and 360 mW near 3.25 μm at 17–20 °C—a nearly or more than twofold increase compared to previous state-of-the-art diode lasers. The utilization of the different quantum wells in the cascade laser heterostructure was demonstrated to yield wide gain lasers, as often desired for tunable laser spectroscopy. Double-step etching was utilized to minimize both the internal optical loss and the lateral current spreading penalties in narrow-ridge lasers. Narrow-ridge cascade diode lasers operate in a CW regime with ~100 mW of output power near and above 3 μm and above 150 mW near 2 μm. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Widely Tunable Monolithic Mid-Infrared Quantum Cascade Lasers Using Super-Structure Grating Reflectors
Received: 1 April 2016 / Revised: 28 April 2016 / Accepted: 29 April 2016 / Published: 3 May 2016
Cited by 4 | PDF Full-text (2845 KB) | HTML Full-text | XML Full-text
Abstract
A monolithic, three-section, and widely tunable mid-infrared (mid-IR) quantum cascade laser (QCL) is demonstrated. This electrically tuned laser consists of a gain section placed between two super structure grating (SSG) distributed Bragg reflectors (DBRs). By varying the injection currents to the two grating [...] Read more.
A monolithic, three-section, and widely tunable mid-infrared (mid-IR) quantum cascade laser (QCL) is demonstrated. This electrically tuned laser consists of a gain section placed between two super structure grating (SSG) distributed Bragg reflectors (DBRs). By varying the injection currents to the two grating sections of this device, its emission wavelength can be tuned from 4.58 μm to 4.77 μm (90 cm−1) with a supermode spacing of 30 nm. This type of SSG-DBR QCLs can be a compact replacement for the external cavity QCL. It has great potential to achieve gap-free and even further tuning ranges for sensor applications. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Dual-Section DFB-QCLs for Multi-Species Trace Gas Analysis
Received: 31 March 2016 / Revised: 27 April 2016 / Accepted: 28 April 2016 / Published: 30 April 2016
Cited by 10 | PDF Full-text (4790 KB) | HTML Full-text | XML Full-text
Abstract
We report on the dynamic behavior of dual-wavelength distributed feedback (DFB) quantum cascade lasers (QCLs) in continuous wave and intermittent continuous wave operation. We investigate inherent etaloning effects based on spectrally resolved light-current-voltage (LIV) characterization and perform time-resolved spectral analysis of thermal chirping [...] Read more.
We report on the dynamic behavior of dual-wavelength distributed feedback (DFB) quantum cascade lasers (QCLs) in continuous wave and intermittent continuous wave operation. We investigate inherent etaloning effects based on spectrally resolved light-current-voltage (LIV) characterization and perform time-resolved spectral analysis of thermal chirping during long (>5 µs) current pulses. The theoretical aspects of the observed behavior are discussed using a combination of finite element method simulations and transfer matrix method calculations of dual-section DFB structures. Based on these results, we demonstrate how the internal etaloning can be minimized using anti-reflective (AR) coatings. Finally, the potential and benefits of these devices for high precision trace gas analysis are demonstrated using a laser absorption spectroscopic setup. Thereby, the atmospherically highly relevant compounds CO2 (including its major isotopologues), CO and N2O are simultaneously determined with a precision of 0.16 ppm, 0.22 ppb and 0.26 ppb, respectively, using a 1-s integration time and an optical path-length of 36 m. This creates exciting new opportunities in the development of compact, multi-species trace gas analyzers. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Influence of Ethanol on Breath Acetone Measurements Using an External Cavity Quantum Cascade Laser
Received: 31 March 2016 / Revised: 22 April 2016 / Accepted: 24 April 2016 / Published: 27 April 2016
Cited by 7 | PDF Full-text (2379 KB) | HTML Full-text | XML Full-text
Abstract
Broadly tunable external cavity quantum cascade lasers (EC-QCLs) in combination with off-axis integrated cavity enhanced spectroscopy (OA-ICOS) provide high molecular gas sensitivity and selectivity. We used an EC-QCL in the region of 1150–1300 cm−1 in both broadband scan mode, as well as [...] Read more.
Broadly tunable external cavity quantum cascade lasers (EC-QCLs) in combination with off-axis integrated cavity enhanced spectroscopy (OA-ICOS) provide high molecular gas sensitivity and selectivity. We used an EC-QCL in the region of 1150–1300 cm−1 in both broadband scan mode, as well as narrow scanning mode around 1216 cm−1, respectively, for detection of acetone in exhaled breath. This wavelength region is essential for accurate determination of breath acetone due to the relative low spectral influence of other endogenous molecules like water, carbon dioxide or methane. We demonstrated that ethanol has a strong spectroscopic influence on the acetone concentration in exhaled breath, an important detail that has been overlooked so far. An ethanol correction is proposed and validated with the reference measurements from a proton-transfer reaction mass spectrometer (PTR-MS) for the same breath samples from ten persons. With the ethanol correction, both broadband and narrowband molecular spectroscopy represent an attractive way to accurately assess the exhaled breath acetone. The importance of considering spectroscopic ethanol influence is essential, especially for the narrowband scans, (e.g., 1216 cm−1), for which the error in determining the acetone concentrations can rise up to 39% if it is not considered. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Enhanced Crystal Quality of AlxIn1-xAsySb1-y for Terahertz Quantum Cascade Lasers
Received: 31 March 2016 / Revised: 14 April 2016 / Accepted: 15 April 2016 / Published: 20 April 2016
Cited by 5 | PDF Full-text (4556 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This work provides a detailed study on the growth of AlxIn1-xAsySb1-y lattice-matched to InAs by Molecular Beam Epitaxy. In order to find the conditions which lead to high crystal quality deep within the miscibility gap, Al [...] Read more.
This work provides a detailed study on the growth of AlxIn1-xAsySb1-y lattice-matched to InAs by Molecular Beam Epitaxy. In order to find the conditions which lead to high crystal quality deep within the miscibility gap, AlxIn1-xAsySb1-y with x = 0.462 was grown at different growth temperatures as well as As2 and Sb2 beam equivalent pressures. The crystal quality of the grown layers was examined by high-resolution X-ray diffraction and atomic force microscopy. It was found that the incorporation of Sb into Al0.462In0.538AsySb1-y is strongly temperature-dependent and reduced growth temperatures are necessary in order to achieve significant Sb mole fractions in the grown layers. At 480 C lattice matching to InAs could not be achieved. At 410 C lattice matching was possible and high quality films of Al0.462In0.538AsySb1-y were obtained. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Continuous Emission Monitoring of Tetrafluoromethane Using Quantum Cascade Lasers
Received: 11 March 2016 / Revised: 29 March 2016 / Accepted: 29 March 2016 / Published: 1 April 2016
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Abstract
Recent developments in quantum cascade lasers have enabled the development of new sensors for in-situ applications that have so far only been possible with extractive systems. In this work, a sensor is presented using a unique Wavelength Modulation Spectroscopy approach to measure tetrafluoromethane, [...] Read more.
Recent developments in quantum cascade lasers have enabled the development of new sensors for in-situ applications that have so far only been possible with extractive systems. In this work, a sensor is presented using a unique Wavelength Modulation Spectroscopy approach to measure tetrafluoromethane, a strong greenhouse gas. The sensor was characterized in a laboratory environment indicating a long-term detection limit of 20 ppb·m and a short-term value of well below 10 ppb·m. To demonstrate the feasibility of the sensor in a real-world environment, it was installed at an Alcoa aluminum smelter. A co-located Fourier Transform Infrared Spectrometer allowed direct comparison measurements of both systems. General agreement between the two methods was observed, leading to the conclusion that the developed in-situ quantum cascade laser based sensor has the potential to continuously measure tetrafluoromethane at aluminum smelters. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Lateral Modes in Quantum Cascade Lasers
Received: 18 February 2016 / Revised: 4 March 2016 / Accepted: 18 March 2016 / Published: 22 March 2016
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Abstract
We will examine the waveguide mode losses in ridge-guided quantum cascade lasers. Our analysis illustrates how the low-loss mode for broad-ridge quantum cascade lasers (QCLs) can be a higher-order lateral waveguide mode that maximizes the feedback from the sloped ridge-wall regions. The results [...] Read more.
We will examine the waveguide mode losses in ridge-guided quantum cascade lasers. Our analysis illustrates how the low-loss mode for broad-ridge quantum cascade lasers (QCLs) can be a higher-order lateral waveguide mode that maximizes the feedback from the sloped ridge-wall regions. The results are in excellent agreement with the near- and far-field data taken on broad-ridge-guided quantum cascade lasers processed with sloped ridge walls. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Review

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Open AccessReview Applying Quantum Cascade Laser Spectroscopy in Plasma Diagnostics
Received: 22 June 2016 / Revised: 19 July 2016 / Accepted: 21 July 2016 / Published: 25 July 2016
Cited by 6 | PDF Full-text (13829 KB) | HTML Full-text | XML Full-text
Abstract
The considerably higher power and wider frequency coverage available from quantum cascade lasers (QCLs) in comparison to lead salt diode lasers has led to substantial advances when QCLs are used in pure and applied infrared spectroscopy. Furthermore, they can be used in both [...] Read more.
The considerably higher power and wider frequency coverage available from quantum cascade lasers (QCLs) in comparison to lead salt diode lasers has led to substantial advances when QCLs are used in pure and applied infrared spectroscopy. Furthermore, they can be used in both pulsed and continuous wave (cw) operation, opening up new possibilities in quantitative time resolved applications in plasmas both in the laboratory and in industry as shown in this article. However, in order to determine absolute concentrations accurately using pulsed QCLs, careful attention has to be paid to features like power saturation phenomena. Hence, we begin with a discussion of the non-linear effects which must be considered when using short or long pulse mode operation. More recently, cw QCLs have been introduced which have the advantage of higher power, better spectral resolution and lower fluctuations in light intensity compared to pulsed devices. They have proved particularly useful in sensing applications in plasmas when very low concentrations have to be monitored. Finally, the use of cw external cavity QCLs (EC-QCLs) for multi species detection is described, using a diagnostics study of a methane/nitrogen plasma as an example. The wide frequency coverage of this type of QCL laser, which is significantly broader than from a distributed feedback QCL (DFB-QCL), is a substantial advantage for multi species detection. Therefore, cw EC-QCLs are state of the art devices and have enormous potential for future plasma diagnostic studies. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessReview Recent Advances in Room Temperature, High-Power Terahertz Quantum Cascade Laser Sources Based on Difference-Frequency Generation
Received: 3 June 2016 / Accepted: 1 July 2016 / Published: 7 July 2016
Cited by 10 | PDF Full-text (2379 KB) | HTML Full-text | XML Full-text
Abstract
We present the current status of high-performance, compact, THz sources based on intracavity nonlinear frequency generation in mid-infrared quantum cascade lasers. Significant performance improvements of our THz sources in the power and wall plug efficiency are achieved by systematic optimizing the device’s active [...] Read more.
We present the current status of high-performance, compact, THz sources based on intracavity nonlinear frequency generation in mid-infrared quantum cascade lasers. Significant performance improvements of our THz sources in the power and wall plug efficiency are achieved by systematic optimizing the device’s active region, waveguide, and chip bonding strategy. High THz power up to 1.9 mW and 0.014 mW for pulsed mode and continuous wave operations at room temperature are demonstrated, respectively. Even higher power and efficiency are envisioned based on enhancements in outcoupling efficiency and mid-IR performance. Our compact THz device with high power and wide tuning range is highly suitable for imaging, sensing, spectroscopy, medical diagnosis, and many other applications. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessReview Progress in Rapidly-Tunable External Cavity Quantum Cascade Lasers with a Frequency-Shifted Feedback
Received: 21 March 2016 / Revised: 11 April 2016 / Accepted: 13 April 2016 / Published: 18 April 2016
Cited by 11 | PDF Full-text (5089 KB) | HTML Full-text | XML Full-text
Abstract
The recent demonstration of external cavity quantum cascade lasers with optical feedback, controlled by an acousto-optic modulator, paves the way to ruggedized infrared laser systems with the capability of tuning the emission wavelength on a microsecond scale. Such systems are of great importance [...] Read more.
The recent demonstration of external cavity quantum cascade lasers with optical feedback, controlled by an acousto-optic modulator, paves the way to ruggedized infrared laser systems with the capability of tuning the emission wavelength on a microsecond scale. Such systems are of great importance for various critical applications requiring ultra-rapid wavelength tuning, including combustion and explosion diagnostics and standoff detection. In this paper, recent research results on these devices are summarized and the advantages of the new configuration are analyzed in the context of practical applications. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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