Multiple-reflection beams for simplified heterodyne interferometers

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Abstract
Heterodyne laser probes are very sensitive noncontacting instruments which provide wide bandwidth and high resolution. Most interferometers are based on a symmetrical two-arms structure, but in all cases, bench scientists know many undesirable beams (due to various reflection) often reduce expected signal to noise ratio. So one major problem of laser probe designers consists in spurious beams elimination. In practice, the so called `spurious beams' can successfully be used for new concepts of heterodyne laser probe. We have verified most assemblies could be simplified (the second arm often becomes useless) and alignment is reduced to minimum. Moreover, optical stability is generally better when using He-Ne laser. The only apparent disadvantage seems to be a small decreasing of the signal to noise ratio (typically about 3 dB, but that value depends on the structure).

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