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Probing of Materials by Pulsed Photoacousitc Techniques

IP.com Disclosure Number: IPCOM000045314D
Original Publication Date: 1983-Mar-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Coufal, H: AUTHOR [+3]

Abstract

Very short photoacoustic pulses, which are produced by a well-localized nitrogen laser beam giving short but intense pulses of radiation, are used to study substrates, such as a sintered ceramic plate. The substrate is black in color, and is observed to be opaque from the near ultraviolet to the far infrared (measured up to the 100-micron wavelength range), thus making conventional optical diagnostic tools very difficult for the bare or coated substrate. The pulsed photoacoustic technique provides some unique diagnostics for such substrates. The nitrogen laser pulse, of about 1-millijoule energy and 10-nanosecond duration, is focused onto the surface of the substrate to a dimension of about 0.1 mm.

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Probing of Materials by Pulsed Photoacousitc Techniques

Very short photoacoustic pulses, which are produced by a well-localized nitrogen laser beam giving short but intense pulses of radiation, are used to study substrates, such as a sintered ceramic plate. The substrate is black in color, and is observed to be opaque from the near ultraviolet to the far infrared (measured up to the 100-micron wavelength range), thus making conventional optical diagnostic tools very difficult for the bare or coated substrate. The pulsed photoacoustic technique provides some unique diagnostics for such substrates. The nitrogen laser pulse, of about 1-millijoule energy and 10-nanosecond duration, is focused onto the surface of the substrate to a dimension of about 0.1 mm. A small polyvinylidene difluoride foil, of about 2 mm diameter and 30- micron thickness, is spring-loaded against an edge of the substrate to detect the photoacoustic signal. The substrate can be moved by a micrometer translation stage so that the separation between the irradiation point and the foil can be accurately varied.

The signals are observed from the piezoelectric foil for two irradiation positions separated by 0.800 inch. The observed signals show that a short ultrasonic pulse (of about 10-nsec duration) is initially generated. This primary pulse produces several effects: (A) It is reflected a few times by the boundaries of the sample, with the reflected pulses remaining sharp. (B) It is attenuated while...