A widely tunable and compact IR laser source emitting in the 9-12 um range based on very efficient phase modulation of CO 2 lasers at microwave frequencies will be constructed and characterized. This laser source consists of a line selecting CO 2 laser, which is stabilized to the 4.3 um emission Lamb-dip, and a traveling-wave CdTe buffered BaAs microstrip electrooptic modulator. With a 20 W microwave drive power, it can provide a continuously tunable IR power output of 10 to 50 mW at frequencies 8 to 18 GHz off-set from the laser carrier frequency. The performance and usefulness of this source will be evaluated and demonstrated by carrying out both direct saturation absorption and hererodyne measurements. The saturation absorption measurements can provide individual line profiles of atomic and molecular transitioons with sub-Doppler resolution. This tunable laser will also be used as a local oscillator in a heterodyne spectrometer which can provide a significant improvement in system sensitivity. An ultra-high resolution and extremely low noise IR heterodyne spectrometer is required for the study of interesting phenomena in the atmospheres of planets occurring in low density, low temperature regions, where sub- Doppler spectral resolution are needed to resolve fully the line shapes and to map spatially the source. The information retrievable from IR heterodyne measurements can accurately determine pressure, temperature, excitation, and molecular abundances of planetary atmospheres. The same technology will find applications in remote sensing measurements of trace gases in the earth's atmosphere.//
