We describe an electronic speckle-pattern interferometry system for analyzing addition fringes generated by the transient deformation of a test object. The system is based on a frequency-doubled twin Nd:YAG laser emitting dual pulses at a TV camera field rate (50 Hz). The main advance has been the automatic, quantitative analysis of dual-pulse addition electronic speckle-pattern interferometry data by the introduction of carrier fringes and the application of Fourier methods. The carrier fringes are introduced between dual pulses by a rotating mirror that tilts the reference beam. The resulting deformation-modulated addition fringes are enhanced with a deviation filter, giving fringe visibility close to that of subtraction fringes. The phase distribution is evaluated with a Fourier-transform method with bandpass filtering. From the wrapped phase distribution, a continuous phase map is reconstructed with an iterative weighted least-squares unwrapper. Preliminary results for a thin plate excited by an acoustic shock show the suitability of the system for the quantitative evaluation of transient deformation fields.
© 1998 Optical Society of America
[Optical Society of America ]
(070.2590) Fourier optics and signal processing : ABCD transforms
(100.5070) Image processing : Phase retrieval
(120.3940) Instrumentation, measurement, and metrology : Metrology
(120.6160) Instrumentation, measurement, and metrology : Speckle interferometry
David I. Farrant, Guillermo H. Kaufmann, Jon N. Petzing, John R. Tyrer, Bob F. Oreb, and David Kerr, "Measurement of Transient Deformations With Dual-Pulse Addition Electronic Speckle-Pattern Interferometry," Appl. Opt. 37, 7259-7267 (1998)