Single-mode distributed-feedback GaAs/AlGaAs quantum well lasers for laser absorption spectroscopy

Abstract

Laser absorption spectroscopy using III-V semiconductor laser diodes has several advantages for gas sensing applications, as compared with traditional methods employing tunable dye laser and II-VI (e.g., lead salt) laser sources. These advantages include room-temperature operation, reduced cost, and compact size. Limited coverage of spectroscopy wavelengths by high-performance III-V lasers has prevented their widespread application to gas sensing. At those fixed wavelengths, performance of commercially available devices has been limited by multimode emission and/or inadequate wavelength tuning and mode hops. These spectra can, however, be greatly improved by incorporating frequency-selective structures. We have developed single-mode distributed-feedback (DFB) GaAs/AlGaAs quantum well lasers applicable to laser spectroscopy of molecules absorbing in the wavelength interval from 760 to 840 nm. These devices exhibit low threshold current ( 40%), high output power (> 25 mW), and narrow linewidth (< 3.0 MHz). The lasers display smooth, continuous, single-mode wavelength tuning over 5 nm. Typical temperature and current wavelength-tuning coefficients are 0.065 nm/ degree(s)C and 0.0075 nm/mA (approximately -3.5 GHz/mA), respectively. In preliminary tests, they have been applied to the detection of H2O vapor and O2 gas.