Laser ultrasonics-based material analysis system and method using matched filter processing

US5604592A · kind A · utility

Assignee

• Textron Defense Systems, Division of Avco Corporation · US

Inventors

• Petros Kotidis · Newton, US
• James Frederick Cunningham · Lincoln, US
• Paul Fred Gozewski · Haverhill, US
• Charles Borsody · Winchester, US
• Daniel E. Klimek · Lexington, US
• Jaime A. Woodroffe · Andover, US

Key dates

• Filing date: Jun 7, 1995
• Grant date: Feb 18, 1997
• Expiry date: Jun 7, 2015

Classification

• Technology area (CPC H): Electricity
• CPC primary: H01S5/02255
• WIPO field: Measurement
• WIPO sector: Instruments

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 techn…