Optical EngineeringAdditive-subtractive speckle interferometry: extraction of phase data in noisy environments
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A technique for realizing accurate phase measurement based on additive-subtractive speckle pattern interferometry is presented. Additive fringe patterns corresponding to two deformation states of an object vibrating sinusoidally are first obtained and these are then subtracted from that with zero deformation. The technique requires five frames of additive speckle patterns S0, S1, ... , S4, where S0 is taken with the laser illumination pulsed at instants when the vibration reaches its two zero amplitude positions within one harmonic vibration cycle of the object, and the remaining four (S1 through S4) are taken with the illumination pulses arranged at times when the vibration reaches its maximum and minimum amplitudes. During the acquisition of S1 through S4, the phase of the reference beam is appropriately shifted between the two pulses within each vibration cycle. The phase shifts are synchronized with the pulses. Speckle patterns S1 through S4 are then subtracted from S0 to generate four correlation fringe patterns with relative phase shifts of 0, ?/2, ? and 3?/2, respectively. These fringe patterns are then utilized to derive a phase map using a four-step phase calculation algorithm and quantitative vibration amplitudes can be readily obtained from the phase map. Results obtained from electronic speckle pattern interferometry and shearography are presented, and the ability of the technique to perform in relatively severe noisy environments is demonstrated.