Patent ID: 6246483
Filing Date: 2001-06-12
Classification: G01B,G01M

Abstract:
Apparatus for inspecting or testing a sample using shearography techniques including:a laser shearing interferometer including:a source of coherent radiation,line generating means for producing a line of coherent radiation from said source,line scanning means for scanning said line of coherent radiation over said sample,shearing element means for generating two laterally displaced images of the sample, andphase stepping or ramping means for stepping or ramping the phase of one of the two images, anda video camera for viewing images of the sample and for providing corresponding video output signals,an image processor operable to receive the video output signals and to extract therefrom the frame rate of the camera in substantially realtime, signal generating means for providing to said stepping or ramping means and said line scanning means a signal substantially in phase with the frame rate of said camera,decoding means for phase extraction,a vacuum chamber for containing at least the laser shearing interferometer and sample,pressure control means capable of varying the pressure within the vacuum chamber between several pre-determined pressure values, andcontrol unit means for interfacing and synchronising said processor, said signal generating means, said decoding means and said pressure control means.