Abstract

For spectroscopy and atmospheric monitoring of trace gases applications which require a continuous-wave (cw) coherent tunable source, infrared (IR) wavelength range can be covered by two principle technologies: (1) lead-salt; (2) nonlinear frequency conversion. The former operates mostly at the temperature below 77 k (for 4.2-15 μm using diffused-junction homogeneous structure ) or up to 120 k (for 3-10.5 μm with double heterostructure) with typical output power of ~100 pW and tuning range per diode of ~100 cm^-1. Based on nonlinear frequency mixing of two lasers in a crystal, difference-frequency generation (DFG) can be realized for the IR region: 3-9 μm with AgGaS₂ and 9-16 μm with GaSe ^[1-2]. As an alternative to diode lasers, DFG IR sources offer large spectral tunability, ultranarrow linewidth, and moderate output power of 1-50 μW.

© 1998 IEEE