MEASUREMENT OF TRANSIENT DEFORMATIONS WITH DUAL-PULSE ADDITION ELECTRONIC SPECKLE-PATTERN INTERFEROMETRY

We describe an electronic speckle-pattern interferometry system for an alyzing addition fringes generated by the transient deformation of a t est object. The system is based on a frequency-doubled twin Nd:YAG las er emitting dual pulses at a TV camera field rate (50 Hz). The main ad vance has been the automatic, quantitative analysis of dual-pulse addi tion electronic speckle-pattern interferometry data by the introductio n of carrier fringes and the application of Fourier methods. The carri er fringes are introduced between dual pulses by a rotating mirror tha t tilts the reference beam. The resulting deformation-modulated additi on fringes are enhanced with a deviation filter, giving fringe visibil ity close to that of subtraction fringes. The phase distribution is ev aluated with a Fourier-transform method with bandpass filtering. From the wrapped phase distribution, a continuous phase map is reconstructe d with an iterative weighted least-squares unwrapper. Preliminary resu lts for a thin plate excited by an acoustic shock show the suitability of the system for the quantitative evaluation of transient deformatio n fields. (C) 1998 Optical Society of America OCIS codes: 120.3940, 12 0.6160, 100.5070, 070.2590.