Patent ID: 6381019
Filing Date: 2002-04-30
Classification: G01N

Abstract:
A method for determining at least one characteristic of a sample comprising a substrate and at least one film disposed on or over a surface of the substrate, comprising steps of:placing a mask over a free surface of the at least one film, the mask having a top surface and a bottom surface that is placed adjacent to the free surface of the film, the bottom surface of the mask comprising a plurality of features forming at least one grating; directing optical pump pulses through the mask to the free surface of the film, individual ones of the pump pulses being followed by at least one optical probe pulse, said pump pulses being spatially distributed by said at least one grating for launching a plurality of spatially distributed strain pulses within the film, said strain pulses causing a change in optical constants of the film; detecting a reflected or transmitted portion of said probe pulses, said probe pulses also being spatially distributed by said at least one grating; measuring a change in at least one characteristic of at least one of reflected or transmitted probe pulses due to the change in optical constants; and determining the at least one characteristic of the sample from the measured change in the at least one characteristic of the probe pulses.