Study on the Development of Laser Instrumentation Beyond the Coherence Length of Laser Diode

An unequal arm interferometer beyond the coherence length of laser diode led to the development of laser instrumentation which is studied theoretically and experimentally in this paper. By using a low-cost diode laser having 650 nm wavelength and short coherence length, a modified Michelson’s interferometer is constructed for the measurements of various physical parameters for long distance measurements. The coherence length is not an abrupt distance. Beyond the coherence length the fringe contrast reduces gradually and becomes indistinguishable. Using better detection techniques, the fringe visibility can be improved to a greater extend. This paper further investigates the other applications of lasers beyond the coherence length.