Abstract
Optical noise is inherent in fringes obtained with the electronic speckle pattern interferometer (ESPI) system. When used in the subtraction mode the optical noise is readily decreased and high contrast fringes may be seen. However, if fast dynamic events are studied a pulsed laser may be used in order to capture particular moments of such an event. A fast repetition rate, 60 pulses per second, Nd:YAG diode seeded laser is introduced in the ESPI system. This laser has twin cavities allowing the firing of two pulses with a minimum time separation, between them, of less than 10 ns. Thus two pulses can be fired within a single TV frame (TV frame rate is 30 Hz) of the ESPI system, interrogating at two different moments in time the fast dynamic event under observation. This process creates a speckle pattern for each pulse, and since two pulses are fired within a single TV frame an addition fringe pattern is obtained, assuming the event has produced a physical measurable change. This addition fringe pattern has an amount of optical noise that is approximately twice that of a subtraction fringe pattern. Results are presented where the addition fringe pattern contrast may be enhanced by using real time electronic filtering.
Published Version
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