Tuning and spectral performance of mid-infrared InAsSb lasers

Tuning and spectral characteristics of 3 mu m wavelength InAsSb lasers were considered in viewpoint of requirements of tunable diode laser absorption spectroscopy (TDLAS). The spectra of lasing, far-field patterns, long term stability, current and temperature tuning performance of CW lasers which are operated at 3.4-3.6 mu m and designed for formaldehyde detection were investigated versus various ambient conditions. A specific characteristic for m-V compound lasers was observed: InAsSb lasers are tuned by direct current to the short wavelength side whereas mode jumps occurred towards longer wavelengths. The lasers showed a good current (up to 950 MHz/mA) and temperature (1.9 GHz/K) tuning. The tuning rate is determined by competition of the electronic and thermal mechanisms of tunability. The thermal shift of the band gap of the active area leads to an average mode tuning rate of about 40 GHz/K. The tuning characteristics were compared with mode jump values to calculate the whole spectral region covered by tunable laser emission. A good stability of the emitted wavelength during a long time period of operating and a lot of cooling-heating cycles could be found, which can be explained by the higher stability of the III-V compound compared to lead-salts. The lasers were suitable for detection of ambient formaldehyde concentration level of 200 pptv @ 1 Hz electronic bandwidth.