Patent ID: 7911603
Filing Date: 2011-03-22
Classification: G01J,G01N

Abstract:
1. A method of measuring the absolute reflectance spectrum of a workpiece using an optical sensing apparatus having a viewing window facing a workpiece support surface, comprising: obtaining a reflectance spectrum of said viewing window; measuring through said viewing window a reflectance spectrum of a reference sample having a predetermined absolute reflectance spectrum, and normalizing the measured reflectance spectrum of said reference sample with said reflectance spectrum of said viewing window; computing a correction function by combining said absolute reflectance spectrum and the normalized reflectance spectrum of said reference sample; for each one of a succession of production workpieces, measuring a reflectance spectrum of the one production workpiece, normalizing said production workpiece reflectance spectrum with the viewing window reflectance spectrum, and computing the production workpiece absolute reflectance spectrum by combining the normalized production workpiece reflectance spectrum with said correction function.