Abstract

A cw tunable infrared spectrometer based on the difference-frequency generation (DFG) in a nonlinear crystal AgGaS₂ (l = 25 mm, noncritical type I phase matching) was constructed as shown in Fig. 1. The system was designed for the wavenumber region around 1900–2100 cm⁻¹. In this spectral region the molecular gases like, CO, N₂O, and NO, have pronounced absorption lines excluding interferences from the major atmospheric gases. As pump source we apply an index-guided diode laser and a tunable dye laser. For trace gas detection we replace the dye laser by a second external tunable diode laser. The diode laser frequency could be coarsely tuned by varying the temperature between −10°C and +40°C providing a wavelength tuning of about 10 nm. For the fine tuning we changed the excitation current. The diode laser frequency is stabilized on a reference Fabry-Perot interferometer (FPI 1). The overall stability was better than 30 MHz over 30 min. An infrared output power of typically 15 nW can be achieved with low powers at the crystal surface (diode-laser 5 mW, dye-laser 150 mW).

© 1996 Optical Society of America