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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Mid-Infrared Fiber-Coupled QCl-QEPAS Sensor

An innovative spectroscopic system based on an external cavity quantum cascade laser (EC-QCL) coupled with a mid-infrared (mid-IR) fiber and quartz enhanced photoacoustic spectroscopy (QEPAS) is described. SF6 has been selected as a target gas in demonstration of the system for trace gas sensing. Single mode laser delivery through the prongs of the quartz tuning fork has been obtained employing a hollow waveguide fiber with inner silver–silver iodine (Ag–AgI) coatings and internal core diameter of 300 lm. A detailed design and realization of the QCL fiber coupling and output collimator system allowed almost practically all (99.4 %) of the laser beam to be transmitted through the spectrophone module. The achieved sensitivity of the system is 50 parts per trillion in 1 s, corresponding to a record for QEPAS normalized noise-equivalent absorption 2.7 9 10-10 W cm-1 Hz-1/2.

External Cavity Quantum Cascade Laser↗
DOE OSTI2016

CW EC-QCL-based sensor for simultaneous detection of H 2 O, HDO, N 2 O and CH 4 using multi-pass absorption spectroscopy

A sensor system based on a continuous wave, external-cavity quantum-cascade laser (CW EC-QCL) was demonstrated for simultaneous detection of atmospheric H 2 O, HDO, N 2 O and CH 4 using a compact, dense pattern multi-pass gas cell with an effective path-length of 57.6 m. The EC-QCL with a mode-hop-free spectral range of 1225-1285 cm -1 operating at similar to 7.8 mu m was scanned covering four neighboring absorption lines, for H 2 O at 1281.161 cm -1 , HDO at 1281.455 cm -1 , N 2 O at 1281.53 cm -1 and CH 4 at 1281.61 cm -1 . A first-harmonic-normalized wavelength modulation spectroscopy with second-harmonic detection (WMS-2f/1f) strategy was employed for data processing. An Allan-Werle deviation analysis indicated that minimum detection limits of 1.77 ppmv for H 2 O, 3.92 ppbv for HDO, 1.43 ppbv for N 2 O, and 2.2 ppbv for CH 4 were achieved with integration times of 50-s, 50-s, 100-s and 129-s, respectively. In conclusion, experimental measurements of ambient air are also reported.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Annual Report for the QCL Calibration Project

Under the Quantum Cascade Laser (QCL) Calibrations project, Pacific Northwest National Laboratory (PNNL) is collaborating with Utah State University and Space Dynamics Laboratory to design, build, and test a QCL calibration source system suitable for insertion into remote sensing platforms. In FY14, the second year of this project, PNNL completed the radiation testing of QCLs using radiation levels that are typical for a space environment. These tests involved both 64-MeV protons, and 1.17-MeV and 1.33-MeV gamma rays. No changes were observed above the measurement uncertainty indicating that QCLs are viable sources for space-based missions. High-level testing was also carried out with gamma rays to determine if QCLs are sensitive to high doses of gamma radiation. After an accumulated dose of 1.5 Mrad(Si), the QCLs continue to demonstrate high performance although a small increase in threshold current, 0.11 ± 0.14% and 0.51 ± 0.15% for M1244D and M664M, respectively, was observed. At this stage, it is unclear if this small increase is from the radiation exposure, because generally it is within the observed experimental uncertainty, which is most likely because of mechanical changes through repeated mounting cycles. There was also some accidental damage to the laser chips and their front facets from the extensive but necessary handling of the devices during these tests. Regardless, the QCLs are robust and should not be susceptible to degradation for most missions.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Implementation of light–matter interaction in NEGF simulations of QCL

The light–matter interaction for the case of stimulated intersubband emission was included through appropriate selfenergy into nonequilibrium Green’s function formalism to simulate electrical and optical characteristics of quantum cascade laser above the lasing threshold.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Thin THz QCL active regions for improved continuous-wave operating temperature

We compare the performance of 10 and 5 μm thick metal–metal waveguide terahertz quantum-cascade laser ridges operating around 2.7 THz and based on a 4-well phonon depopulation active region design. Thanks to reduced heat dissipation and lower thermal resistance, the 5 μm thick material shows an 18 K increase in continuous wave operating temperature compared to the 10 μm material, despite a lower maximum pulsed-mode operating temperature and a larger input power density. A maximum continuous wave operating temperature of 129 K is achieved using the 5 μm thick material and a 15 μm wide ridge waveguide, which lased up to 155 K in the pulsed mode. The use of thin active regions is likely to become increasingly important to address the increasing input power density of emerging 2- and 3-well active region designs that show the highest pulsed operating temperatures.

47 OTHER INSTRUMENTATION↗
NASA NTRS2010

Widely Tunable Mode-Hop-Free External-Cavity Quantum Cascade Laser

The external-cavity quantum cascade laser (EC-QCL) system is based on an optical configuration of the Littrow type. It is a room-temperature, continuous wave, widely tunable, mode-hop-free, mid-infrared, EC-QCL spectroscopic source. It has a single-mode tuning range of 155 cm(exp -1) (approximately equal to 8% of the center wavelength) with a maximum power of 11.1 mW and 182 cm(exp -1) (approximately equal to 15% of the center wavelength), and a maximum power of 50 mW as demonstrated for 5.3 micron and 8.4 micron EC-QCLs, respectively. This technology is particularly suitable for high-resolution spectroscopic applications, multi-species tracegas detection, and spectroscopic measurements of broadband absorbers. Wavelength tuning of EC-QCL spectroscopic source can be implemented by varying three independent parameters of the laser: (1) the optical length of the gain medium (which, in this case, is equivalent to QCL injection current modulation), (2) the length of the EC (which can be independently varied in the Rice EC-QCL setup), and (3) the angle of beam incidence at the diffraction grating (frequency tuning related directly to angular dispersion of the grating). All three mechanisms of frequency tuning have been demonstrated and are required to obtain a true mode-hop-free laser frequency tuning. The precise frequency tuning characteristics of the EC-QCL output have been characterized using a variety of diagnostic tools available at Rice University (e.g., a monochromator, FTIR spectrometer, and a Fabry-Perot spectrometer). Spectroscopic results were compared with available databases (such as HITRAN, PNNL, EPA, and NIST). These enable precision verification of complete spectral parameters of the EC-QCL, such as wavelength, tuning range, tuning characteristics, and line width. The output power of the EC-QCL is determined by the performance of the QC laser chip, its operating conditions, and parameters of the QC laser cavity such as mirror reflectivity or intracavity losses. In order to maximize the output power, an analysis and optimization of the EC laser parameters has been performed. The parameters of the beam emitted from the gain medium, such as divergence angle, beam profile, and astigmatism, have been investigated. The gain medium has been fully characterized before and after each stage of modification. The main modification steps are coating one facet of the gain chip with a high reflectivity mirror and the other facet with an anti-reflection layer. Then the chip is mounted in the EC-QCL. The optomechanical design has been reviewed and improved to provide for precise collimation of the strongly divergent beam of the QCL and the tuning diffraction grating.

Wysocki, Gerard↗
DOE OSTI2014

Analysis of geometric phase effects in the quantum-classical Liouville formalism

We analyze two approaches to the quantum-classical Liouville (QCL) formalism that differ in the order of two operations: Wigner transformation and projection onto adiabatic electronic states. The analysis is carried out on a two-dimensional linear vibronic model where geometric phase (GP) effects arising from a conical intersection profoundly affect nuclear dynamics. We find that the Wigner-then-Adiabatic (WA) QCL approach captures GP effects, whereas the Adiabatic-then-Wigner (AW) QCL approach does not. Moreover, the Wigner transform in AW-QCL leads to an ill-defined Fourier transform of double-valued functions. The double-valued character of these functions stems from the nontrivial GP of adiabatic electronic states in the presence of a conical intersection. In contrast, WA-QCL avoids this issue by starting with the Wigner transform of single-valued quantities of the full problem. As a consequence, GP effects in WA-QCL can be associated with a dynamical term in the corresponding equation of motion. Since the WA-QCL approach uses solely the adiabatic potentials and non-adiabatic derivative couplings as an input, our results indicate that WA-QCL can capture GP effects in two-state crossing problems using first-principles electronic structure calculations without prior diabatization or introduction of explicit phase factors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Electrical tuning of a terahertz quantum cascade laser based on detuned intersubband absorption

A mechanism to electrically tune the frequency of terahertz quantum cascade lasers (QCLs) is developed that allows for tuning, while the QCL is operated close to its peak bias and temperature. Two optically coupled but electrically isolated cavities are used in which the bias of a control cavity tunes the resonant-mode of the coupled QCL cavity independent of the QCL's operating bias. Approximately 4 GHz electrical tuning is realized for a 3.6 THz distributed-feedback QCL operating in pulsed mode at 58 K in a Stirling cooler. The single-mode QCL emits near-constant peak-power in the range of 5$-$5.3 mW through the tuning range and radiates in a narrow single-lobed beam with a far-field divergence of ~4°×11°. The superlattice structure of the QCL is designed to implement a low-voltage intersubband absorption transition that is detuned from that of its gain transition, the strength of which could be controlled sensitively with applied voltage utilizing resonant-tunneling injection of electrons in the absorption subband. Finally, the tuning is realized by the application of small bias voltages (~6$-$7 V) and requires a narrow bias range (~1 V, ~40 A/cm 2 ) to traverse across the entire tuning range, and the method should be generally applicable to all intersubband lasers including mid-infrared QCLs.

42 ENGINEERING↗
DOE OSTI2021

Quantum cascade laser with monolithically integrated passive waveguide

A photonic integrated circuit device includes a passive waveguide section formed over a substrate, a quantum cascade laser (QCL) gain section formed over the substrate and adjacent to the passive waveguide section, and a taper section disposed between and in contact with each of the passive waveguide section and the QCL gain section. In some embodiments, the passive waveguide section includes a passive waveguide core layer disposed between a first cladding layer and a second cladding layer. In some examples, the QCL gain section includes a QCL active region disposed between a first confinement layer and a second confinement layer, where the QCL active region has a lower index of refraction than each of the first and second confinement layers. In some embodiments, the taper section is configured to optically couple the QCL gain section to the passive waveguide section.

Jung, Seungyong↗
DOE OSTI2015

Investigation of giant Kerr nonlinearity in quantum cascade lasers using mid-infrared femtosecond pulses

We study the Kerr nonlinearity of quantum cascade lasers (QCLs) by coupling resonant and off-resonant mid-infrared (mid-IR) femtosecond (fs) pulses into an active QCL waveguide. We observe an increase in the spectral width of the transmitted fs pulses as the coupled mid-infrared (mid-IR) pulse power increases. This is explained by the self-phase modulation effect due to the large Kerr nonlinearity of QCL waveguides. We further confirm this effect by observing the intensity dependent far-field profile of the transmitted mid-IR pulses, showing the pulses undergo self-focusing as they propagate through the active QCL due to the intensity dependent refractive index. We experimentally estimate the nonlinear refractive index n{sub 2} of a QCL to be ∼8 × 10{sup −9 }cm{sup 2}/W using the far-field beam profile of the transmitted pulses. The finite-difference time-domain simulations of QCL waveguides with Kerr nonlinearity incorporated show similar behavior to the experimental results.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Spectral modification of the laser emission of a terahertz quantum cascade laser induced by broad-band double pulse injection seeding

We demonstrate by injection seeding that the spectral emission of a terahertz (THz) quantum cascade laser (QCL) can be modified with broad-band THz pulses whose bandwidths are greater than the QCL bandwidth. Two broad-band THz pulses delayed in time imprint a modulation on the single THz pulse spectrum. The resulting spectrum is used to injection seed the THz QCL. By varying the time delay between the THz pulses, the amplitude distribution of the QCL longitudinal modes is modified. By applying this approach, the QCL emission is reversibly switched from multi-mode to single mode emission.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2010

Piezo activated mode tracking system for widely tunable mode-hop-free external cavity mid-IR semiconductor lasers

A widely tunable, mode-hop-free semiconductor laser operating in the mid-IR comprises a QCL laser chip having an effective QCL cavity length, a diffraction grating defining a grating angle and an external cavity length with respect to said chip, and means for controlling the QCL cavity length, the external cavity length, and the grating angle. The laser of claim 1 wherein said chip may be tuned over a range of frequencies even in the absence of an anti-reflective coating. The diffraction grating is controllably pivotable and translatable relative to said chip and the effective QCL cavity length can be adjusted by varying the injection current to the chip. The laser can be used for high resolution spectroscopic applications and multi species trace-gas detection. Mode-hopping is avoided by controlling the effective QCL cavity length, the external cavity length, and the grating angle so as to replicate a virtual pivot point.

Wysocki, Gerard↗
DOE OSTI2013

Detection and measurement of electroreflectance on quantum cascade laser device using Fourier transform infrared microscope

We demonstrate the use of a Fourier Transform Infrared microscope system to detect and measure electroreflectance (ER) from mid-infrared quantum cascade laser (QCL) device. To characterize intersubband transition (ISBT) energies in a functioning QCL device, a microscope is used to focus the probe on the QCL cleaved mirror. The measured ER spectra exhibit resonance features associated to ISBTs under applied electric field in agreement with the numerical calculations and comparable to observed photocurrent, and emission peaks. The method demonstrates the potential as a characterization tool for QCL devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

A widely tunable 10-μm quantum cascade laser phase-locked to a state-of-the-art mid-infrared reference for precision molecular spectroscopy

We report the coherent phase-locking of a quantum cascade laser (QCL) at 10-μm to the secondary frequency standard of this spectral region, a CO{sub 2} laser stabilized on a saturated absorption line of OsO{sub 4}. The stability and accuracy of the standard are transferred to the QCL resulting in a line width of the order of 10 Hz, and leading to the narrowest QCL to date. The locked QCL is then used to perform absorption spectroscopy spanning 6 GHz of NH{sub 3} and methyltrioxorhenium, two species of interest for applications in precision measurements.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Single mode terahertz quantum cascade amplifier

A terahertz (THz) optical amplifier based on a 2.9 THz quantum cascade laser (QCL) structure has been demonstrated. By depositing an antireflective coating on the QCL facet, the laser mirror losses are enhanced to fully suppress the lasing action, creating a THz quantum cascade (QC) amplifier. Terahertz radiation amplification has been obtained, by coupling a separate multi-mode THz QCL of the same active region design to the QC amplifier. A bare cavity gain is achieved and shows excellent agreement with the lasing spectrum from the original QCL without the antireflective coating. Furthermore, a maximum optical gain of ∼30 dB with single-mode radiation output is demonstrated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2005

Frequency and Phase-lock Control of a 3 THz Quantum Cascade Laser

We have locked the frequency of a 3 THz quantum cascade laser (QCL) to that of a far-infrared gas laser with a tunable microwave offset frequency. The locked QCL line shape is essentially Gaussian, with linewidths of 65 and 141 kHz at the -3 and -10 dB levels, respectively. The lock condition can be maintained indefinitely, without requiring temperature or bias current regulation of the QCL other than that provided by the lock error signal. The result demonstrates that a terahertz QCL can be frequency controlled with l-part-in-lO(exp 8) accuracy, which is a factor of 100 better than that needed for a local oscillator in a heterodyne receiver for atmospheric and astronomic spectroscopy.

Betz, A. L.↗