Continuous-wave Room Temperature Quantum Research Articles

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.

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.

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).

Real-time measurements of atmospheric CO using a continuous-wave room temperature quantum cascade laser based spectrometer

A compact, mobile mid-infrared laser spectrometer based on a thermoelectrically (TE) cooled continuous-wave room temperature quantum cascade laser and TE-cooled detectors has been newly developed to demonstrate the applicability of high sensitivity and high precision measurements of atmospheric CO. Performance of the instrument was examined with periodic measurements of reference sample and ambient air at 1 Hz sampling rate and a 1-hourly calibration cycle. The typical precision evaluated from replicate measurements of reference sample over the course of 66-h is 1.41 ppbv. With the utilization of wavelet filtering to improve the spectral SNR and minimize the dispersion of concentration values, a better precision of 0.88 ppbv and a lower detection limit of ~0.4 ppbv with sub-second averaging time have been achieved without reducing the fast temporal response. Allan variance analysis indicates a CO measurement precision of ~0.28 ppbv for optimal integration time of approximate 50 s. The absolute accuracy is limited by the calibration gas standard. This completely thermoelectrically cooled system shows the capability of long-term, unattended and continuous operation at room temperature without complicated cryogenic cooling.

From CO2 lasers to quantum cascade lasers—A saga of high power infrared lasers

The era of high continuous laser power in the infrared region of the spectrum started with the first demonstration of laser action on the vibrational-rotational transitions of molecules and the invention of the carbon dioxide laser [C. K. N. Patel, “Interpretation of CO2 Optical Maser Experiments,” Phys. Rev. Lett. 12, 588–590 (1964)] in 1964. The progress in the high power molecular lasers was swift and led to an explosion of scientific and practical applications in the infrared. The romance with high power infrared lasers that started with in 1964 is still very much alive today. New types of infrared lasers, notably the quantum cascade lasers (QCLs) are carving out a special niche in this arena. Applications of these lasers abound, both in science and industry. In reviewing the fun and excitement of the past as well as what may be in store for us in the future, I will focus on the current impact of the high power midwave and long wave infrared QCLs [A. Lyakh, C. Pflügl, L. Diehl, Q. J. Wang, Federico Capasso, X. J. Wang, J. Y. Fan, T. Tanbun-Ek, R. Maulini, A. Tsekoun, R. Go, and C. Kumar N. Patel, “1.6 Watt, High Wallplug Efficiency, Continuous-Wave Room Temperature Quantum Cascade Laser Emitting at 4.6 μm,” Appl. Phys. Lett. 92, 111110 (2008)] in many defense and homeland security related applications [C. K. N. Patel, “Laser Photoacoustic Spectroscopy Helps Fight Terrorism: High Sensitivity Detection of Chemical Warfare Agent and Explosives,” Eur. Phys. J. Spec. Top. 153, 1–18 (2008)]. In this paper I will recount some of the key advances in the high power lasers and their applications.

1.6 W high wall plug efficiency, continuous-wave room temperature quantum cascade laser emitting at 4.6μm

A strain-balanced, InP-based quantum cascade laser structure designed for light emission at 4.6μm was grown by metal-organic chemical vapor deposition. A maximum total optical power of 1.6W was obtained in continuous-wave mode at 300K for uncoated devices processed in buried heterostructure geometry with stripe dimensions of 5mm by 9.5μm. Corresponding maximum wall plug efficiency and threshold current density were measured to be 8.8% and 1.05kA∕cm2, respectively. Fully hermetically packaged laser of identical dimensions produced in excess of 1.5W under the same conditions.