Bae Systems, Inc.

British Aerospace Public Limited Company

Phillip Langley Salter

Steve Carl Jamieson Parker

Steve C J Parker

Steve C Parker

John P Smith

The signal to noise ratio in non-destructive testing or evaluation of a sample (,) by in phase stepped optical inspection systems such as the optical shearography system using a shearing interferometer involves production of correlated speckle images successively stepped in phase by illuminating with coherent radiation a sample in an unstressed state, illuminating the sample with coherent radiation, stressing it incrementally at predetermined stress increments, and generating and capturing correlated speckle images successively stepped in phase of the incrementally stressed sample at the predetermined stress increments, using the phase stepped speckle images of the unstressed and incrementally stressed sample to calculate the phase before and after stressing and differencing the images to extract the incremental phase change, inspecting the magnitude and sign of each incremental phase change and if the phase difference between successive measurements increases by more than &pgr; subtracting 2 &pgr; from the measurement value or if the phase difference between successive measurements decreases by more than &pgr; adding 2 &pgr; to the measurement value, and calculating the phase at each point in each speckle image by summing the nearest neighbour phase differences in the image that are weighted by the square of their respective modulations, where the modulation is a measure of intensity variation with phase variation and normalising the result of this calculation by dividing by the sum of the modulations.

Method for increasing the signal-to-noise ratio in non-destructive testing

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. A pressure control varies the pressure within the vacuum chamber between several predetermined pressure values and a control unit interfaces and synchronizes the processor, the signal generator, the decoder and the pressure control.

Apparatus and method for shearographic inspection and non-destructive testing of articles in a vacuum chamber

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.

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Bristol, United Kingdom

Phillip Langley Salter