Abstract: A collimated laser diode associated with a small, short focal length objective lens produces a focused laser beam on the top of a sample glued onto a piezoelectric transducer. This laser beam is horizontally scanned on the surface and its intensity is modulated by a square wave using a TTL signal generator. This system induces acoustic waves in the sample. With a specially designed control circuitry, by combining this acoustic signal and the scanned laser beam, imaging of the subsurface is possible. The transient analysis developed is described and we show how to select cut-away views of the subsurface specimen with some applications in failure analysis of integrated circuits. We present the apparatus, the transient photoacoustic signal theory, and make a comparison between scanning photoacoustic (SPAM) and scanning electron acoustic microscopy (SEAM). !7
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