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

Abstract

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.