Abstract

Publisher Summary This chapter discusses theoretical and experimental considerations related to the coherent detection in the middle infrared, particularly at the 10.6 μ CO 2 laser wavelength. Coherent (heterodyne) detection is well known in the radio wave, microwave, and optical regions of the electromagnetic spectrum. Recently the technique is extended to the middle infrared as well. Coherent detection differs in several significant respects from direct detection, or simple photon counting. In particular, the increased sensitivity available through its use in the infrared allows the detection of far weaker signals than by means of any other technique. Because the setup employed in these experiments detects the scattered radiation from a diffusely reflecting moving surface, it is, in effect, a miniature prototype CO 2 laser radar. Experiments on the power-spectraldensity and the envelope probability distribution of the homodyne signal are also discussed in the chapter.

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