Optical system including interferometer for enhancing the performance of

Abstract

An interferometer for transmitting a beam of electromagnetic energy toward a target, portions of the transmitted beam reflected by the target being directed onto a detecting surface of a detector element with a local oscillator beam to provide a beat frequency signal representative of, for example, target range. The interferometer comprises a first lens for focusing the target-reflected return beam onto substantially a point on a detecting surface. The interferometer additionally comprises a second lens, for example, for focusing the local oscillator beam through a focal point onto the first lens. The first and second lenses are disposed to align such focal point of the second lens with a focal point of the first lens to thereby direct the local oscillator beam onto the detecting surface of the detector element with a substantially uniform intensity distribution thereon. With such arrangement, the detector element may be implemented as a photoconductive, rather than a photovoltaic, detector with only a minimal net increase in the noise equivalent power (NEP) thereof, such as 5 dB, resulting in similar slight reduction in the signal-to-noise ratio of the interferometer. Since such photoconductive detector element may be cooled by thermoelectric stacks, the requirement for liquid nitrogen coolant is eliminated, thereby significantly reducing the size and weight of the interferometer system.