Method and system for optical evaluation, and optical detector

Abstract

An optical detector 50 comprises a plurality of pixels, each pixel comprising a photodiode operable to detect light incident on that pixel and to generate a signal indicative of an intensity of that light. The plurality of pixels comprises a plurality of pixel pairs, and for each pixel pair, in a configuration mode, the detector is arranged to compare the signal generated by a first pixel of the pair with the signal generated by a second pixel of the pair. The plurality of pixels may comprise an array and the signal indicative of intensity generated by each pixel may be connected to either a first output 52 or a second output 54 depending on the result of the comparison. In an experiment mode, the signals indicative of intensity received at the first output 52 may be summed and those received at the second output 54 may be summed. The difference between the two summed signals may be obtained. The optical detector may be a speckle knife edge detector used in laser ultrasonic evaluation of both rough and smooth surfaces.

Description

technical field [0001] The present invention relates to methods and systems for optical evaluation, and optical detectors for use in such methods and systems. The invention relates particularly, but not exclusively, to the optical detection of ultrasound waves on the surface of a material. Background technique [0002] Ultrasound is widely used to detect material defects, wear, cracks, etc., and has the key advantage of allowing the inspection of optically opaque materials. The problem with traditional (non-laser) ultrasound is that it requires contact sensors to generate and detect ultrasonic waves. This means that the method is not suitable for inaccessible or hazardous environments. Laser hypersonics overcomes these problems by using lasers to generate and detect sound waves. A laser generates sound by heating a sample causing thermal expansion, thereby generating acoustic waves, typically comprising surface acoustic waves (SAW), that propagate across the surface of th...

AI Technical Summary

Problems solved by technology

[0003] Laser ultrasound, however, is not without its own problems, the main one being that when the sample we want to examine is 'rough' like many engineering parts (here, rough only means underpolished, which is not very good mirror), the light is scattered randomly, and conventional optical techniques will not be able to detect the presence of sound waves passing under the beam

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