ABSTRACT
The feedback or self-mixing configuration of interferometry (SMI) deserves special consideration for its unique properties of minimum-part count, compactness and simplicity of use. Injection at low feedback level is first analyzed, and a He-Ne based instrument is developed. Then, feedback at medium level is studied by the Lang-Kobayashi equation and the three-mirror model, and a laser-diode SMI is worked out, by half fringe counting, and its precision and accuracy are evaluated. An SMI vibrometer is then developed, on the idea of the half-fringe locking through a feedback servo loop, obtaining sensitivity better than 100 pm and linear response up to 0.1mm. The vibrometer is applied to: detection of the modes of a structure, measurement of mechanical hysteresis, and MEMS diagnostics. Further applications of SMI described in the chapter include: absolute distance measurement, angle and radius of curvature measurement, detection of weak optical echoes, CD readout, measurement of physical quantities (linewidth, alpha factor of lasers), and measurement of biological signals (blood pulsation, respiratory sounds).
