Two‐frequency Lidar technique for mesospheric Na temperature measurements

We describe a new two‐frequency lidar for measuring Na temperature profiles that uses a stabilized cw single‐mode dye laser oscillator (rms frequency jitter < 1 MH_z) followed by a pulsed‐dye power amplifier (140 MHz FWHM linewidth) which is pumped by an injection‐locked Nd: YAG laser. The laser oscillator is tuned to the two operating frequencies by observing the Doppler‐free structure of the Na D₂ fluorescence spectrum in a vapor cell. The lidar technique and our initial observations of the temperature profile between 82 and 102 km at Ft. Collins, CO (40.6°N,105°W) are described. Absolute temperature accuracies at the Na layer peak of better than ±3 K with a vertical resolution of 1 km and an integration period of approximately 5 min were achieved.