Method and instrument for detection of change of thickness or refractive index for a thin film substrate

A method for optimizing an instrument configured and arranged to detect a change in thickness or refractive index of a thin film substrate, said instrument comprising:

• a light source providing monochromatic light that is linearly polarized, positioned at an angle other than Brewster's angle relative to the substrate;
• an incident polarizer;
• and
• a detector and analyzing polarizer positioned at said angle relative to said substrate at a location suitable for detecting reflected polarized light from said substrate, comprising the step of:
• positioning the analyzing polarizer relative to the incident polarizer so as to minimize polarization rotation or ellipticity of the light reflected from said substrate prior to said change in thickness or refractive index and so as to maximize the change in polarization rotation or ellipticity as measured by the intensity of light reflected from said substrate that is transmitted to said detector upon said change in thickness or refractive index of said substrate.

A method for detecting a change in thickness or refractive index of a thin film substrate comprising, utilizing an optical instrument comprising;

• a source of linearly polarized light positioned at an angle other than Brewster's angle relative to said substrate;
• an incident polarizer;
• a detector and an analyzing polarizer positioned at said angle relative to said substrate at a location suitable for detecting reflected polarized light from said substrate;
• and
• said analyzing polarizer is further positioned to maximize any change in polarization rotation or ellipticity as measured by the change in intensity of light reflected from the substrate that is transmitted to the detector when said thickness or refractive index of said substrate is changed, comprising the steps of:
• a) changing the thickness or refractive index of said substrate;
• and
• b) detecting with said detector said change in intensity of light reflected from said substrate when said substrate is changed in thickness or refractive index.