Room-temperature Quantum Cascade Laser Research Articles

Millimeter-wave generation with a room-temperature nonlinear quantum cascade laser

Millimeter-wave difference frequency generation is reported for a dual-wavelength mid-infrared quantum cascade laser operating at room temperature. To overcome a low mid-infrared-to-terahertz conversion efficiency below 1 THz, a long-wavelength, high-performance mid-infrared quantum cascade laser structure with higher nonlinear susceptivity is adopted. By designing the efficient allocation of mid-infrared pumps to two sections of fabricated distributed feedback grating, a closely separated dual-wavelength (λ1 ∼ 13.53 μm and λ2 ∼ 13.39 μm) laser oscillation was obtained. Consequently, a millimeter-wave emission at a frequency of 231 GHz was successfully observed at room temperature.

Fast-sweeping continuous wave quantum cascade laser operating in an external cavity with polygon mirror.

We report a continuous wave room temperature quantum cascade laser operating in an external cavity in the Littrow configuration with a 10-facet polygon mirror rotating at 24,000 RPM. The quantum cascade laser emission is swept across ∼1520 - 1625 cm-1 wavenumber range in less than ∼45 µs with a sweep repetition rate of 4 kHz. The measured maximum output power at the laser gain maximum, 15°C and 0.86 A driving current is ∼90 mW; the estimated average output power across the 45 µs wavenumber sweep is ∼50 mW. Through its sweep, the laser emits on the sequential Fabry-Perot longitudinal modes of the laser chip cavity with the mode separation of ∼0.5 cm-1. The linewidth of the emitting modes is less than ∼0.05 cm-1. Spectral measurements of the infrared absorption features of a 10 µm thick layer of acetophenone and water vapor in the air have demonstrated the capability of obtaining spectral data in less than 45 µs.

Room‐temperature quantum cascade laser packaged module at ∼8 μm designed for high‐frequency response

A high-speed, room-temperature quantum cascade laser packaged module emitting at 8.14 μm is presented. The cavity length of the laser is as small as 0.5 mm, and the threshold current at 298 K is 110 mA. A matching printed circuit board is inserted into the packaged module to reduce the RC constant. As a result, the rectification response of packaged module is relatively flat upto 2 GHz and the –3 dB cut-off frequency is increased from 0.9 to 2.2 GHz.

Room-temperature quantum-cascade lasers with nonlinear optical difference-frequency generation

Room-temperature quantum-cascade lasers with nonlinear optical difference-frequency generation

Watt-level, high wall plug efficiency, continuous-wave room temperature quantum cascade laser emitting at 7.7µm.

In this article, a InP based strain-balanced In0.58Ga0.42As/In0.47Al0.53As quantum cascade laser emitting at 7.7µm is reported. The active region is based on a slightly-diagonal bound to continuum design with 50 cascade stages and a low voltage defect Δinj of 96 meV. By optimizing the active region and waveguide structure, the waveguide loss αw of 1.18cm-1 are obtained, which contribute to a high wall-plug efficiency (WPE) of 9.08% and low threshold current of only 1.09 kA/cm2 in continuous-wave(CW) operation at 293K. The maximum single facet output power of 1.17W in CW operation and 2.3W in pulsed operation are measured at 293K. The narrow ridge and buried ridge structure epi-side-down-mounted on the diamond heatsink improved the heat dissipation of the device. A beam of pure zero order mode and a broad external-cavity tuning range from 7.16µm to 8.16µm are also achieved.

Room temperature quantum cascade laser with ∼31% wall-plug efficiency

In this article, we report the demonstration of a quantum cascade laser emitting at λ ≈ 4.9 μm with a wall-plug efficiency of ∼31% and an output power of ∼23 W in pulsed operation at room temperature with 50 cascade stages (Ns). With proper fabrication and packaging, this buried ridge quantum cascade laser with a cavity length of 5 mm delivers more than ∼15 W output power, and its wall-plug efficiency exceeds ∼20% at 100 °C. The experimental results of the lasers are well in agreement with the numerical predictions.

Room temperature quantum cascade lasers with 22% wall plug efficiency in continuous-wave operation.

We report the demonstration of quantum cascade lasers (QCLs) with improved efficiency emitting at a wavelength of 4.9 µm in pulsed and continuous-wave (CW) operation. Based on an established design and guided by simulation, the number of QCL-emitting stages is increased in order to realize a 29.3% wall plug efficiency (WPE) in pulsed operation at room temperature. With proper fabrication and packaging, a 5-mm-long, 8-µm-wide QCL with a buried ridge waveguide is capable of 22% CW WPE and 5.6 W CW output power at room temperature. This corresponds to an extremely high optical density at the output facet of ∼35 MW/cm2, without any damage.

High power continuous wave operation of single mode quantum cascade lasers up to 5 W spanning λ∼3.8-8.3 µm.

In this work, we report high power continuous wave room-temperature operation single mode quantum cascade lasers in the mid-infrared spectral range from 3.8 to 8.3 µm. Single mode robustness and dynamic range are enhanced by optimizing the distributed feedback grating coupling design and the facet coatings. High power single mode operation is secured by circumventing the over-coupling issue and spatial hole burning effect. Maximum single-facet continuous-wave output power of 5.1 W and wall plug efficiency of 16.6% is achieved at room temperature. Single mode operation with a side mode suppression ratio of 30 dB and single-lobed far field with negligible beam steering is observed. The significantly increased power for single mode emission will boost the QCL applications in long-range free-space communication and remote sensing of hazardous chemicals.

An adaptive Kalman filtering algorithm based on back-propagation (BP) neural network applied for simultaneously detection of exhaled CO and N2O.

A compact high-resolution spectroscopic sensor using a thermoelectrically (TE) cooled continuous-wave (CW) room temperature (RT) quantum cascade laser (QCL) was demonstrated for simultaneous measurements of exhaled carbon monoxide (CO) and nitrous oxide (N2O). The sampling pressure was optimized to improve the sensitivity, the optimal pressure was determined to be 150 mbar based on an optical density analysis of simulated and measured absorption spectra. An adaptive Kalman filtering algorithm based on back-propagation (BP) neural network was developed and proposed for real-time exhaled breath analysis in order to perform fast and high precision on-line measurements. The detection limits (1σ) of 1.14 ppb and 1.12 ppb were experimentally achieved for CO and N2O detection, respectively. Typical concentrations of exhaled CO and N2O from smokers and non-smokers were analyzed. The experimental results indicated that the state-of-the-art CW-QCL based sensor has a great potential for non-invasive, on-line identification and quantification of biomarkers in human breath.

High-power, continuous-wave, phase-locked quantum cascade laser arrays emitting at 8 µm.

We report a room-temperature eight-element phase-locked quantum cascade laser array emitting at 8 µm with a high continuous-wave power of 8.2 W and wall plug efficiency of 9.5%. The laser array operates primarily via the in-phase supermode and has single-mode emission with a side-mode suppression ratio of ~20 dB. The quantum cascade laser active region is based on a high differential gain (8.7 cm/kA) and low voltage defect (90 meV) design. A record high wall plug efficiency of 20.4% is achieved from a low loss buried ridge type single-element Fabry-Perot laser operating in pulsed mode at 20 °C.

ZnO-based terahertz quantum cascade lasers

High-power terahertz sources operating at room-temperature are promising for many applications such as explosive materials detection, non-invasive medical imaging, and high speed telecommunication. Here we report the results of a simulation study, which shows the significantly improved performance of room-temperature terahertz quantum cascade lasers (THz QCLs) based on a ZnMgO/ZnO material system employing a 2-well design scheme with variable barrier heights and a delta-doped injector well. We found that by varying and optimizing constituent layer widths and doping level of the injector well, high power performance of THz QCLs can be achieved at room temperature: optical gain and radiation frequency is varied from 108 cm −1 @ 2.18 THz to 300 cm −1 @ 4.96 THz. These results show that among II–VI compounds the ZnMgO/ZnO material system is optimally suited for high-performance room-temperature THz QCLs.

Quantum cascade laser based absorption spectroscopy for direct monitoring of atmospheric N2O isotopes

A compact high-resolution spectroscopic sensor using a thermoelectrically (TE) cooled continuous-wave (CW) room temperature (RT) quantum cascade laser (QCL) operating at 4.6 μm, is employed for simultaneous detection of three main isotopic species (14N15N16O, 15N14N16O and 14N14N16O). To enable a high-precision analysis of N2O isotopic species at ambient mixing ratios, a liquid nitrogen-free preconcentration unit is built to trap and load atmospheric N2O. The absorption spectra of 14N15N16O, 15N14N16O, and 14N14N16O between 2188.6 cm−1 and 2189 cm−1 are measured, and the respective ratios of the rare to the abundant isotopologues abundances are demonstrated. Moreover, spectroscopic parameters of pressure-broadening coefficient for selected absorption lines have been determined, and a good agreement is obtained by comparing with HITRAN database.

Part per trillion nitric oxide measurement by optical feedback cavity-enhanced absorption spectroscopy in the mid-infrared

While nitric oxide (NO) is being monitored in various fields of application, there is still a lack of available instruments at a sub-ppb level of sensitivity. We report on the first application of Optical Feedback Cavity-Enhanced Absorption Spectroscopy (OF-CEAS) to NO trace gas analysis, with a room-temperature quantum-cascade laser at 5.26 µm (1900.5 cm $$^{-1}$$ ). A detection limit of 60 ppt is reached in a single measurement performed in 140 ms. The stability of the instrument allows to average for 10 s down to 8.3 ppt, limited by drift of etalon fringes in the spectra. This work opens the path towards new applications notably in breath analysis and environment sciences.

Simultaneously Photoacoustic Measurement of Carbon Dioxide and Nitrous Oxide Using a Quantum Cascade Laser

In this paper a photoacoustic senor for carbon dioxide and nitrous oxide detection is described which uses a quantum cascade laser. The sensor relies on a 4.43 μm continuous-wave room temperature quantum-cascade laser source and a homemade photoacoustic cell based on a cylindrical acoustic resonator. Primary laboratory tests have been performed for estimation of the achievable detection limits and possible applications for in situ and real time atmosphere measurements. It is demonstrated that the minimum detectable concentration of 13CO2 and N2O under laboratory conditions is 8 ppbv and 0.45 ppbv, respectively.

Ultra-broadband room-temperature terahertz quantum cascade laser sources based on difference frequency generation.

We present ultra-broadband room temperature monolithic terahertz quantum cascade laser (QCL) sources based on intra-cavity difference frequency generation, emitting continuously more than one octave in frequency between 1.6 and 3.8 THz, with a peak output power of ~200 μW. Broadband terahertz emission is realized by nonlinear mixing between single-mode and multi-mode spectra due to distributed feedback grating and Fabry-Perot cavity, respectively, in a mid-infrared QCL with dual-upper-state active region design. Besides, at low temperature of 150 K, the device produces a peak power of ~1.0 mW with a broadband THz emission centered at 2.5 THz, ranging from 1.5 to 3.7 THz.

Simultaneous atmospheric CO, N2O and H2O detection using a single quantum cascade laser sensor based on dual-spectroscopy techniques

A single continuous wave (CW) room-temperature (RT) quantum cascade laser (QCL) sensor based on dual spectroscopic techniques was demonstrated and developed for simultaneous measurement of atmospheric carbon monoxide (CO), nitrous oxide (N2O) and water vapor (H2O). The newly developed detection scheme combines the benefits of absolute concentration measurements using calibration-free direct absorption spectroscopy (DAS) with higher sensitive wavelength modulation spectroscopy (WMS), which offers the possibility of calibration-free trace gases concentration detection with a 3–4 fold improvement in measurement precision and a significant decrease in optimal signal averaging time. By using the DAS calibrated WMS-2f detection scheme, Allan deviation analysis indicates that measurement precision of 1.64ppb for CO, 1.15ppb for N2O and 50.4ppm for H2O was achieved with a 1-s integration time, which can be further improved to 0.21ppb, 0.18ppb and 5.65ppm by averaging up to 75s.

Generation of Kerr combs centered at 4.5 μm in crystalline microresonators pumped with quantum-cascade lasers.

We report on the generation of mid-infrared Kerr frequency combs in high-finesse CaF2 and MgF2 whispering-gallery-mode resonators pumped with continuous-wave room-temperature quantum cascade lasers. The combs were centered at 4.5 μm, the longest wavelength to date. A frequency comb wider than one half of an octave was demonstrated when approximately 20 mW of pump power was coupled to an MgF2 resonator characterized with quality factor exceeding 10(8).

Simultaneous measurement of NO and NO(2) by dual-wavelength quantum cascade laser spectroscopy.

The concept of a multi-wavelength quantum cascade laser emitting at two or more spectrally well-separated wavelengths is highly appealing for applied spectroscopy, as it allows detecting several species with compact and cost-efficient optical setups. Here we present a practical realization of such a dual-wavelength setup, which is based on a room-temperature quantum cascade laser emitting single-mode at 1600 cm-1 and 1900 cm-1 and is thus well-suited for simultaneous NO and NO2 detection. Operated in a time-division multiplexed mode, our spectrometer reaches detection limits of 0.5 and 1.5 ppb for NO2 and NO, respectively. The performance of the system is validated against the well-established chemiluminescence detection while measuring the NOx emissions on an automotive test-bench, as well as upon monitoring the pollution at a suburban site.

室温连续中红外量子级联激光器驱动电源的研制

室温连续中红外量子级联激光器驱动电源的研制

Site-selective nitrogen isotopic ratio measurement of nitrous oxide using a TE-cooled CW-RT-QCL based spectrometer

The feasibility of laser spectroscopic isotopic composition measurements of atmospheric N2O was demonstrated, although making them useful will require further improvements. The system relies on a thermoelectrically (TE) cooled continuous-wave (CW) room temperature (RT) quantum cascade laser source emitting wavelength of around 4.6μm, where strong fundamental absorption bands occur for the considered specie and its isotopomers. The analysis technique is based on wavelength modulation spectroscopy with second-harmonic detection and the combination of long-path absorption cell. Primary laboratory tests have been performed to estimate the achievable detection limits and the signal reproducibility levels in view of possible measurements of 15N/14N and 18O/16O isotope ratios. The experiment results showed that the site-selective 15N/14N ratio can be measured with a precision of 3‰ with 90s averaging time using natural-abundance N2O sample of 12.7ppm.