OPTICALLY PUMPED SUBMILLIMETER LASER HETERODYNE RECEIVERS - ASTROPHYSICAL OBSERVATIONS AND RECENT TECHNICAL DEVELOPMENTS

NASA is planning a series of submillimeter space missions beginning with the Small Explorer Submillimeter Wave Astronomy Satellite, due to be launched in 1995, followed by the Submillimeter Intermediate Mission, and eventually culminating in the observatory-class Large Deployable Reflector. During the 1990's, submillimeter observations at both high mountain sites and on the Kuiper Airborne Observatory and its planned replacement, the Stratospheric Observatory for Infrared Astronomy, will play important active roles in submillimeter observations. The technical challenges faced by experimenters in extending terahertz receiver technology for space operations are daunting. A recent NASA study, the Astrotech 21 Workshop, has pointed out the pressing need for suitable local oscillator (LO) sources for future submillimeter space missions. Optically pumped submillimeter lasers currently provide the only proven LO source for heterodyne receivers in the 600-3000 GHz range. Laser heterodyne receiver systems have been productively used for many years for ground-based and airborne observations. The submillimeter laser, the heart of the system, represents the heaviest and largest component of a heterodyne receiver system. These lasers can now be reduced by a factor of 3-5 in size and weight using new technologies such as RF-excited waveguide CO2 laser pumps and novel submillimeter cavity designs. This paper will review both ground-based and airborne astrophysical applications of laser heterodyne receivers and will present recent technical developments which may allow such systems to be utilized for future space missions.