ASA 125th Meeting Ottawa 1993 May

1pPA3. Using piezoelectric film and resonant ultrasound for photoacoustic measurements of very low optical absorption in piezoelectric and dielectric crystals.

M. J. McKenna

Wei-Li Lin

J. D. Maynard

Dept. of Phys., Penn State Univ., University Park, PA 16802

The photoacoustic effect is one of the most sensitive methods for measurements of the low optical absorption in glasses and crystals. Previously, a new photoacoustic technique has been developed, where a cw laser modulated at the acoustic resonant frequency of the sample generates an acoustic signal amplified by the quality factor of the resonance. With typical quality factors in the order of 10[sup 5], this technique is several orders of magnitude more sensitive than conventional pulsed-laser techniques. However, previous applications using noncontact capactive transducers required precise postitioning of the sample, transducers, and seperate sample supports. Recently, this difficulty has been reduced through the use of 9-(mu)m-thick piezoelectric (PVDF) film transducers. By supporting the sample at the corners between the film transducers, the need for separate supports is eliminated, with only a small reduction in the quality factor of the resonance. In addition, a large improvement in the signal-to-noise ratio is observed. Recent measurements on large single crystals of calcium floride and quartz will be discussed. [Work supported by NSF Grant No. DMR-9000549 and by the Office of Naval Research.]