A tunable CO2laser sideband spectrometer

Abstract

We describe a high-resolution spectrometer for the 9-11 \mu m wavelength region, which is tunable over 23 GHz wide regions below and above each of some 80 CO 2 laser lines. An electrooptic modulator mixes the frequency-stabilized CO 2 laser output (frequency f L ) with tunable microwave signals (frequency f M ) to produce tunable, spectrally pure ( \pm1 \times 10^{-8} ) sidebands in the IR, whose frequencies f_{L} \pm f_{M} are readily determined with high precision ( \pm2 \times 10^{-7} ). The design of traveling wave and resonant modulators and associated tuners is given and discussed. The usefulness of the instrument for high resolution absorption spectroscopy and as a tunable local oscillator for heterodyne spectroscopy is demonstrated.