Enhancing the sensitivity to small phase changes in double-exposure stroboscopic television holography

We present a new technique for enhancing the sensitivity of double-exposure stroboscopic television holography (TVH) to detect and measure vibrations of small amplitude. The technique is based in the modulation of the phase o f the reference beam in synchronism with the vibration of the measurand and derives from a former technique that we originally contrived for phase eva luation. We propose two variants, characterized by the demodulation process used to generate the secondary correlograms, with different behaviors in t erms of the sensitivity to the sign of the measurand and of the ease in det ecting the presence and shape of the vibration. We have implemented this ne w technique in an electronic speckle-pattern interferometer and compared it s performance with standard TVH techniques; vibrations with amplitudes as s mall as 8 nm have been observed with this setup. (C) 2000 Optical Society o f America OCIS codes: 120.0120, 120.6160, 120.7280.