Recently, nonlinear ultrasound, especially subharmonics, is highly expected to be a tool for detecting and evaluating closed cracks. Considering the above, we have constructed a Subharmonic Phased Array for Crack Evaluation (SPACE). However, the SPACE with piezoelectric array sensor could not receive wideband frequency components because of the frequency characteristics of the sensor. The present array sensor also had problems in that the in-plane information was averaged and the freedom of the system was limited. In this study, to expand frequency bandwidth and to realize flexible array configuration, we propose laser SPACE that could image the defects by scanning laser interferometer, filtering the received waveforms, matching the phase using delay law and extracting feature quantity. This enables us to image the defects using subharmonics or second harmonics and construct a 2 dimension array that provides detailed information of the thickness direction of the crack. In addition, it is a useful tool for designing optimized elements layout of a piezoelectric 2 dimensional array. In this paper, we formulated imaging algorithms of laser SPACE and applied it to a linear defect and a fatigue crack. Closed parts of the fatigue crack were imaged by subharmonic components only. Additionally, by comparing the results with images provided by a piezo SPACE, we demonstrate the advantage of laser SPACE.

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A non-contact and precise longitudinal velocity measurement technique, for temperature measurement in semiconductor processing, was developed using a combination of 100 MHz narrow-band laser ultrasound and a pulse-echo-overlap technique. A diffraction correction method for laser ultrasound, based on a Gaussian weighted circular source — a point detection model, was also developed to enhance the accuracy of echo period measurements. It was shown that the longitudinal velocity in 10mm thick single crystal silicon can be measured with a resolution of better than 0.01% . It was also shown that the temperature of a 0.6mm thick silicon wafer can be evaluated with a resolution higher than 2^oC at 500^oC and 1000^oC.

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