Pulsed Submillimeter Laser Program.

This report describes the results of an exploratory development program to investigate various system and component aspects of a pulsed FIR heterodyning laser radar. During the course of this developmental program a number of interrelated subsystems required for a heterodyning FIR radar were investigated. The work focused on optically pumped FIR lasers which utilize a CO2 laser pump source. Pulsed FIR and CO2 pump lasers are required for the primary radar transmitter, and CW FIR and CO2 lasers are needed for the laser radar local oscillator. The transversely excited (TE) CO2 laser which serves as the pulsed FIR laser pump is itself a central component of the radar system and the performance characteristics of a recirculating, high pulse repetition frequency (PRF) TE CO2 as a FIR pump were experimentally examined. A number of different pulsed FIR laser resonators were investigated with the objective of minimizing system size. The requirement for a stable FIR local oscillator imposes certain constraints on the CW CO2 pump source and a stable single mode CO2 pump source has been designed and characterized. A sealed-off CW FIR laser with an Invar stabilized cavity was constructed for use as a local oscillator source. A number of detectors for use at submillimeter wavelength were examined and pulsed and CW detection with two micron Schottky diodes were performed. Because of the extreme sensitivity of the CW FIR laser and pump source to temperature fluctuation a technique for stabilizing the CO2 utilizing the photoacoustic effect in the FIR medium was examined and found to be very promising.