Abstract: Disclosed is an apparatus and method for inspecting or testing a sample using shearography techniques. A laser shearing interferometer includes: a source of coherent radiation, a line generator producing a line of coherent radiation from said source, a line scanner scans the line of coherent radiation over the sample, a shearing element generates two laterally displaced images of the sample, and phase stepper or ramper steps or ramps the phase of one of the two images. A video camera views images of the sample and provides corresponding video output signals. An image processor receives the video output signals and extracts therefrom the frame rate of the camera in substantially realtime. A signal generator provides the stepper and the line scanner, a signal substantially in phase with the frame rate of the camera, a decoder is used for phase extraction and a vacuum chamber contains the laser shearing interferometer and the sample under test.

Abstract: A sample (1) is inspected or tested by illumination in which a line of coherent radiation (2) is scanned across the sample (1) with zero shear in the direction of scan. Two laterally displaced images of the sample (1) are generated which are phase stepped by stepping or ramping the phase of one of the two images during each of the line scans so that successive lines are incremented in phase to encode temporally information about the sample in one frame. The encoded information is decoded by running a vertical convolution mask (17) over the encoded frame image.