Submillimeter receivers: local oscillators and mixers

Abstract

With submillimetric (SUBMM) devices, lasers and mixers, the classical microwave techniques may be extended up to the SUBMM range. The best choice for the local oscillator seems to be the optically pumped FIR laser because of the high number of active lines, output power and frequency stability. For the last one, values as low as delta sub y (tau) = 2 x 10 to - 13 power tau to the -1/2 power for tau less than or equal to 20 and a minimum measured value delta sub y (100 ms) = 2 x 10 to the -12th were obtained for the CH3OH pumped laser. For a high IF bandwidth, high multiplication order and high frequency operation, the classical mixers used in microwaves may be extended to the SUBMM as well as to the IR spectrum. Some of them have sensitivities to the quantum limit. Since an analysis of the optical wave propagation in the atmospheric for inclement weather operation has shown the useful windows on the SUBMM range, a SUBMM receiver appears to be very promising to operate in the battlefield on fog, rain and snow as active imaging system.