Ultrasonic-based material analysis using an annular impulse beam

Details Ultrasonic-based material analysis using an annular impulse beam Ultrasonic-based material analysis using an annular impulse beam

1997-02-14

1998-08-11

Font, Frank G.

Optics: measuring and testing

By dispersed light spectroscopy

Utilizing a spectrometer

356432, G01B 902

Patent

active

057934894

ABSTRACT:
Disclosed herein is an interferometric-based materials analysis system (10) that employs a novel combination of laser beam shaping and pointing techniques, the use of a low cost, rugged, and compact diode laser (22) as a detection laser, and the use of signal processing techniques that compensate for inherent instabilities and short-term drift in the diode laser. A matched filter processing technique is disclosed for processing interferometrically-obtained data points from a target being analyzed. The matched filter technique is shown to be especially useful for detecting and analyzing Lamb modes within thin targets, such as a silicon wafer undergoing a rapid thermal processing cycle. Also disclosed is a method and apparatus for interferometrically monitoring a target to determine, in accordance with predetermined criteria, an occurrence of a period of time that is optimum for obtaining a data point. In response to detecting such a period an impulse source, such as an impulse laser (14), is triggered to launch an elastic wave within the target so that a data point can be obtained. A plurality of data points so obtained are subsequently processed, such as by the matched filter technique, to determine a property of interest of the target. The property of interest may be, by example, the temperature of the target or the metallurgical status of the target.

REFERENCES:
Scruby et al., "Laser Ultrasonics Techniques and Applications" National Nondestructive Testing Centre, ACA Technology, Harwell Laboratory, pp. 324-351, date not available.

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