MAPPING OF VIBRATION AMPLITUDES BY TIME-AVERAGE HOLOGRAPHY IN BI12SIO20 CRYSTALS

We report the performance of a holographic set-up with a Bi12SiO20 (BS O) photorefractive crystal for measuring vibration amplitudes in a tim e average holography system. The volume hologram is recorded with the 514.5 nm wavelength of an Ar+ laser. In this set-up the reference beam is sinusoidally phase-modulated with the same frequency of the vibrat ing object. By increasing the value of the phase modulation, the fring es of the time average pattern run along the object surface, so that t he vibration amplitude mapping is carried out. This technique allows t he improvement of the measurement sensitivity compared with convention al time average holography, even for interferograms with poor visibili ty. (C) 1998 Elsevier Science Ltd. All rights reserved.