Saturated-absorption spectroscopy with low-power difference-frequency radiation

We report high-resolution saturated-absorption spectra recorded by use of a few microwatts of radiation generated in a single pass by difference-frequency mixing. These results were obtained without the use of buildup cavities for the nonlinear mixing or for the saturation spectroscopy. We show high-quality saturated-absorption signals for the fundamental rovibrational band of CO2 near 4.3 mu m. Convenient sources and frequency-conversion devices open new possibilities for sub-Doppler spectroscopy in the infrared. (C) 2000 Optical Society of America OCIS codes: 300.6460, 190.2620, 300.6340, 300.6390, 300.6320.