The research presented first introduces Digital Phase Demodulation concepts and shows initial experimental results from a heterodyne interferometer. The initial results show that the heterodyne sensor system is capable of measuring displacements greater than 1.5 wave lengths of light and has a single shot resolution better than 3 nm. Thus Digital Phase Demodulation will allow a single instrument to monitor displacements produced by low amplitude, high frequency ultrasound and by high amplitude, low frequency vibrations.; Next, a laser cavity is injection locked to a small portion of its own light which is diffusely backscattered into the laser cavity by a moving object. The laser cavity provides both large amplification of the backscattered light and gain control while the backscattered light forces the laser cavity to resonate with the frequency and phase of the return light in a stable manner. The backscattered light from the object can be collected by the laser cavity without the help of any focussing optics. Thus Injection Locked Laser sensors relax the requirements for a precise and robust optical alignment necessary for industrial applications. This dissertation introduces Injection Locked Laser theory, develops two Injection Locked Laser sensors, and presents measurements from the sensors while monitoring vibrational and ultrasonic displacements.
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