Interferometry using a laser as radiation source, amplifier and detector

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Abstract
The photon induced current changes in a DC laser produced by optical feedback from an external cavity are shown to be a convenient means of monitoring interference in the laser interferometer. Experiments are carried out using a helium-neon laser operated at 0.6328 and 3.39 mu m wavelengths with variation in path length of the external cavity produced by piezoelectric movement of the external mirror. The frequency response of the voltage fringes appearing across the laser tube is shown to be somewhat less than that of the conventional optical fringes; however in the present case fringing frequencies of 500 kHz were readily observed. Closer investigation using very narrow optical fringes showed that the frequency response of the voltage fringes was determined by their 4 mu s decay time. This technique could be a great asset to laser interferometry in the infrared where radiation detectors are expensive and of low sensitivity.

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