A tunable diode-laser spectrometer for the MIR region near 7.2 μm applying difference-frequency generation in AgGaSe2

The design and first experiments with a tunable high-resolution cw difference-frequency spectrometer applying non-critical phasematching type I (90 degrees) in AgGaSe2 and two diode lasers as pump sources are presented. A single-mode Fabry-Perot-type tunable diode laser (TDL) and an external-cavity diode laser (ECL) were combined to generate radiation in the mid-infrared region near 7.2 mu m. With a TDL at a wavelength of approximately 1290 nm and an ECL emitting between 1504 and 1589 nm it was possible to carry out spectroscopic experiments concerning SO2 at five different phasematching points between 1350 and 1400 cm(-1) by fixing the wavelength of one pump laser and tuning the wavelength of the other. With an input power of 8 mW for the single-mode Fabry-Perot-type diode laser and 6 mW for the external-cavity laser an output power of about 10 nW was generated. Using the tuning capabilities of the external-cavity laser a spectral region up to 5 cm(-1) could be covered within one scan. Measurements of SO2 absorption lines at low pressure demonstrate the high-resolution features of the spectrometer. Moreover, these data provide new direct experimental phasematching data for the rarely investigated spectral region at 7.2 mu m.