Patent ID: 7193712

Claim:
A method of measuring an electromagnetic radiation response property associated with a substrate, the method comprising: producing electromagnetic waves which pass through a first polarized filter before the electromagnetic waves reach the substrate, the first polarized filter having a first optical axis; capturing a portion of the electromagnetic waves after the portion of the electromagnetic waves reflect off the substrate and pass through a second polarized filter, the second polarized filter having a second optical axis, the first optical axis being non-parallel with the second optical axis; determining a first light intensity value associated with a first coordinate of the substrate from the captured portion of the electromagnetic waves; determining a second light intensity value associated with a second coordinate of the substrate from the captured portion of the electromagnetic waves, the second light intensity value being different than the first light intensity value, the second coordinate being different than the first coordinate; and storing a representation of the first light intensity value and the second light intensity value in an electronic storage device; wherein introducing electromagnetic waves comprises termination of a light pulse by a chop circuit, wherein the chop circuit terminates in response to a detection of a predetermined amount of electromagnetic radiation reflected from the substrate.