Dmitri Z. Garbuzov

Continuous-wave operation of λ=3.25 μm broadened-waveguide W quantum-well diode lasers up to T=195 K

Mid-infrared (λ=3.25 μm) broadened-waveguide diode lasers with active regions consisting of 5 type-II “W” quantum wells operated in continuous-wave (cw) mode up to 195 K. At 78 K, the threshold current density was 63 A/cm2, and up to 140 mW of cw output power was generated. A second structure with ten quantum wells operated up to 310 K in pulsed mode.

Ultralow‐loss broadened‐waveguide high‐power 2 μm AlGaAsSb/InGaAsSb/GaSb separate‐confinement quantum‐well lasers

Broadening the waveguides of 2 μm AlGaAsSb/InGaAsSb separate‐confinement multiquantum‐well lasers decreases their internal losses to 2 cm−1, while threshold current densities remain as low as 300 A/cm2. The consequently high cw differential efficiency of 0.36 results in output powers of 1.2 W from 100 μm aperture lasers at 15 °C.

Room‐temperature 2.78 μm AlGaAsSb/InGaAsSb quantum‐well lasers

We describe room‐temperature 2.78 μm AlGaAsSb/InGaAsSb multiquantum well lasers. Pulsed laser operation was observed at 15 °C with a threshold current of 1.1 A (10 kA/cm2), and a maximum power output of 30 mW, and a maximum differential quantum efficiency of 9%. Lasers operated pulsed up to 60 °C with a characteristic temperature of 58 K over the range of 0–40 °C. To date, 2.78 μm is the longest emission wavelength for a room‐temperature III–V laser.

High-power separate-confinement heterostructure AlGaAs/GaAs laser diodes with broadened waveguide

AlGaAs/GaAs graded-index separate-confinement heterostructure single quantum well (GRINSCH-SQW) lasers with different waveguide thickness have been analyzed experimentally and compared with results from modeling using transverse optical field distributions. We have found that for GRINSCH lasers the halfwidth of near-field and far-field patterns depends very weakly on the waveguide thickness due to the focusing of the optical field in the transverse direction by the graded-index waveguide. At the same time, the mode intensity in the cladding layers is reduced by two orders of magnitude as the waveguide thickness is increased from 40 nm to 1200 nm. As a result, a 20% improvement in the differential quantum efficiency ((eta) d) is realized, while the threshold current density remains unchanged. Differential quantum efficiency as high as 78% and output power exceeding 4 W cw have been obtained for broadened waveguide lasers.

A potential remote sensor of CO in vehicle exhausts using 2.3 µm diode lasers

The potential for on-road remote sensing of vehicle exhausts using 2.3 µm diode-laser-absorption-based CO sensors is examined. Using a wavelength-modulation- spectroscopy (WMS) technique, 20 ppm sensitivity with a detection bandwidth of 1.5 kHz is demonstrated in laboratory experiments, which implies the ability to monitor CO emissions from even the cleanest combustion-powered vehicles. The influence of the temperature and composition of the exhaust gas on the inferred CO concentration through both linestrength and linewidth is also investigated and we propose a novel approach to reduce these effects to ±3% in the typical exhaust temperature range of 300-700 K. Thus, sensitive and remote measurements of vehicular CO effluent are possible without knowing the exact temperature or composition of the exhaust. This influence of temperature is further exploited to suggest a two-line CO2-absorption thermometry method with a large temperature sensitivity to identify cold-start vehicles.

2.78 μm InGaAsSb/AlGaAsSb multiple quantum-well lasers with metastable InGaAsSb wells grown by molecular beam epitaxy

Abstract Multiple quantum-well (MQW) lasers with metastable InGaAsSb quantum wells and AlGaAsSb barriers and claddings were grown on n+−GaSb(100) substrates by molecular beam epitaxy. The lasers exhibited a lasing wavelength of 2.78 μm and pulsed operation up to 60°C. Pulsed threshold current of 1.1 A, corresponding to a current density of 9.5 kA/cm2, and maximum output power of 30 mW have been achieved at 15°C for broad-area lasers. The characteristic temperature was 58 K over the temperature range of 0 to 40°C. This is the longest emission wavelength reported for quantum-well lasers operating at room temperature.

New room temperature CW InGaAsSb/AlGaAsSb QW ridge diode lasers and their application to CO measurements near 2.3 μm

In this work the spectral characteristics of a new type of mid-infrared diode laser are discussed and an application for CO trace gas detection is demonstrated. The InGaAsSb/AlGaAsSb QW diode lasers operating in the spectral range of 2.0 - 2.7 micrometer in continuous wave (CW) regime at room temperature (RT) were developed last year. Earlier, the spectral range of RT CW operation for diode lasers was limited by 2.0 - 2.1 micrometer. The extension of wavelength to 2.7 micrometer was achieved for InGaAsSb/AlGaAsSb quantum well (QW) lasers by employing for QWs new quasi-ternary InGaSb(As) compositions that are out of the miscibility gap for InGaAsSb materials. Single spatial mode ridge lasers emitting at 2.2 - 2.7 micrometer have parameters similar to those of the infrared lasers with (lambda) less than 2 micrometer widely used for spectroscopic application. At operating currents about 80 - 200 mA and temperatures up to +50 degrees Celsius, these lasers emit CW output power of several milliwatts. Investigation of the laser spectra has revealed the current and temperature ranges where a single longitudinal mode dominates with side mode suppression of 22 - 25 dB. The dominant mode can be tuned in wavelength by varying current or temperature. The lasers were used to record high-resolution CO absorption lineshapes (2v band near 2.3 micrometer) in a static cell (14.9-cm path). Probed CO transitions were selected for applications to in situ measurements in high- temperature combustion flows. In general, the measured CO absorption lineshapes agreed with theoretical Voigt profiles calculated using the HITRAN database to within 2%. For a minimum detectable absorbance of 0.01% and a 1-meter long path, the CO measurement sensitivity for the probed R30 transition near 2.302 micrometer was 5 - 10 ppm at 1000 K. This value is about two orders of magnitude better than the sensitivity reported for CO detection with conventional diode lasers that probe transitions in the 3v band near 1.56 micrometer.

High-power broadened-waveguide InGaAsSb/AlGaAsSb quantum well diode lasers emitting at 2 μm

We review our recent progress in the design and operation of 2-micrometer InGaAsSb/AlGaAsSb quantum-well diode lasers. The devices have InGaAsSb quantum-well active regions and AlGaAsSb cladding layers, and all were grown lattice-matched to GaSb substrates using molecular-beam epitaxy. The broadened- waveguide (BW) design produces internal losses as low as 2 cm-1, which leads to external quantum efficiencies as high as 53%. Single-quantum-well lasers with 200-micrometer apertures and 2-mm-long cavities exhibit output powers of 1.9 W CW and 4 W quasi-CW. The lowest threshold current densities are 115 A/cm2. Small arrays of similar multi-quantum-well- diodes emit 10.6 W CW. The broadened-waveguide design should improve the performance of all mid-infrared diode lasers.

Tunable single-frequency III-V semiconductor diode lasers with wavelengths from 0.76 to 2.7 μm

We have fabricated single-frequency diode lasers from a number of III-V semiconducting compounds. These diode lasers were specifically designed for laser absorption spectroscopy. Their emission wavelengths span the internal of 0.76 to 2.7 micrometers . Water vapor, CO, CO2, NH3, CH4 HF, and O2 have been detected using them. After a brief review of their physical structure and principles of operation, we present representative output characteristics of these lasers, along with a discussion of several important applications.

Mid-infrared W quantum-well lasers for noncryogenic continuous-wave operation

We review the recent progress of electrically injected and optically pumped mid-IR lasers based on antimonide quantum wells with the type II W configuration. W quantum-well diodes have achieved cw operation up to 195 K at lambda = 3.25 mum. Optically pumped devices that employ the diamond pressure bond heat sink have reached 290 K at 3 mum and 210 K at 6 mum. Pulsed power conversion efficiencies of up to 7% at 220 K have been attained by use of an optical pumping injection cavity approach, in which an etalon cavity for the pump beam significantly enhances its absorptance. The angled-grating distributed-feedback configuration has been used to obtain near-diffraction-limited output for an optical pumping stripe width of 50 mum.