A new instrument for measuring low level linear birefringence

Summary form only given. Modern optical instruments, such as semiconductor photolithography equipment, require increasingly low levels of birefringence in lenses, masks and laser windows. Traditional techniques lack the sensitivity required, are cumbersome and time consuming and are not readily adapted for scanning a sample. Hinds Instruments has developed a highly sensitive instrument (Exicor/sup TM/) for rapid automatic scanning of samples of optical materials in two dimensions. This yields both the magnitude and direction of the "average birefringence" for each measurement point. The method employs a HeNe laser, a photoelastic modulator (PEM), calcite polarizers and photoconductive detectors in a unique 2-channel detection system. The two channels measure birefringence at two orthogonal directions 45 degrees apart, giving complete information for determination of the magnitude and direction of birefringence at each measurement point.