Application of antimonide lasers for gas sensing in the 3-4-microm range

Antimonide semiconductor laser devices designed for continuous-wave emission in the 3-4-mum spectral range have been investigated with respect to spectroscopic applications. Representative data on the mode structure, output power, noise characteristics, far-field pattern, and modulation response are presented. Selected laser devices have been applied for methane (CH(4)) and formaldehyde (HCHO) measurements by use of a high-frequency modulated diode laser spectrometer. From an Allan variance analysis of experimental data a detection limit for HCHO of 120 pptv (where 1 pptv = 10(-12) volume mixing ratio) with a 40-s integration time and for CH(4) of 2 ppbv (where 1 ppbv = 10(-9) volume mixing ratio) with 20-s integration time were determined. The results show that, for selected gases, InAsSb lasers can be an alternative to lead-salt diode lasers.