A tunable CO₂laser sideband spectrometer

We describe a high-resolution spectrometer for the9-11 wavelength region, which is tunable over 23 GHz wide regions below and above each of some 80 CO2laser lines. An electrooptic modulator mixes the frequency-stabilized CO2laser output (frequency fL) with tunable microwave signals (frequency fM) to produce tunable, spectrally pure (±1 × 10⁻⁸) sidebands in the IR, whose frequenciesfL ± fMare readily determined with high precision (±2 × 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.