In TV holography (also called ESPI or DSPI), temporal phase stepping is a common method. It allows quantitative evaluation of high quality interferograms of quasi-static events and of harmonic vibrations. To study transient and rapid events, pulsed lasers with pulses of short duration (about 25 ns) are instead employed. This 'freezes' most mechanical and acoustic events, such as propagating transient bending waves and acoustic fields. A recently developed pulsed TV holography system allows all-electronic recording and evaluation of interferograms. Two object state recordings are captured on subsequent frames using a CCD-camera connected to a PC computer. The time separation can be set from 20 microseconds to 700 microseconds using a double pulsed ruby laser. Phase maps are calculated and unwrapped to give 3D-plots of the deformation or pressure fields. Recordings of bending wave propagation in plates and transient sound fields in air will illustrate the system performance.
Nils-Erik Molin, Nils-Erik Molin,
"Pulsed TV holography system: development and some results", Proc. SPIE 3407, International Conference on Applied Optical Metrology, (29 September 1998); doi: 10.1117/12.323306; https://doi.org/10.1117/12.323306