Patent ID: 6445457
Filing Date: 2002-09-03
Classification: G01B

Abstract:
A method for measuring a material layer thickness comprising:(a) contacting a surface of a material with a first laser pulse at a light wavelength that heats the surface of the material to generate an acoustical pulse that reverberates within the material to periodically displace the surface; (b) directing a second laser pulse having a pulse length greater than the pulse length of the first laser pulse onto the surface of the material that is heated by the first laser pulse at an oblique angle effective to reflect from the surface; (c) placing a detector at a location effective to detect reflections of the second laser pulse from the surface; (d) detecting angular variations in the reflections of the second laser pulse as the surface is displaced; (e) determining the frequency of the angular variations wherein the material thickness is inversely related to the frequency.