Method and apparatus for detecting photoacoustic signal

Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system

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356432, 73602, G01N 2188, G01N 2125

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active

051361728

ABSTRACT:
A method and apparatus are disclosed for detection of surface defects and internal defect information of a sample, such as a semiconductor device, using the photoacoustic effect. Operationally, an intensity-modulated laser beam is provided having a predetermined desired frequency. The intensity-modulated laser beam is focused on the sample thereby inducing said photoacoustic effect inside the sample which is detected in two-dimensional directions of the sample so as to compose a two-dimensional photoacoustic image of the excited sample. Surface and internal information of the sample is then extracted from the two-dimensional photoacoustic image and an inverse filtering factor is in turn computed on the basis of a thermal impulse response of the particular sample for compensating degradation of the resolution of the actual photoacoustic image obtained. Lastly, the computed inverse filtering factor is then applied to the detected photoacoustic image to arrive at an image having greatly improved resolution.

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A. D. Poularikas et al., Signals and Systems, 1985, p. 242.
Masanori Hangyo, et al., "Photoacoustic Microscope", Department of Applied Physics, Faculty of Engineering OSAKA University, (Hihakai Kensa, Nondestructive Testing), vol. 36, No. 10, Oct. 1987, pp. 730-736.
P. Cielo, et al., "Laser Generation of Convergent Acoustic Waves and Applications to Materials Evaluation", IEEE 1986 Ultrasonics Symposium, pp. 515-526.

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