Patent ID: 7224457
Filing Date: 2007-05-29
Classification: G01J,G01N

Abstract:
1. A method for measuring retardation of materials, the method comprising the steps of: providing a light source for transmitting light along a light transmission axis; fixing a polarizer along the light transmission axis in the path of the transmitted light, the polarizer having a polarization transmission direction substantially perpendicular to the light transmission axis; positioning an analyzer along the light transmission axis, the analyzer having a polarization transmission direction substantially perpendicular to the light transmission axis; interposing a first waveplate between the polarizer and the analyzer, the first waveplate being located along the light transmission axis, the first waveplate having a slow axis, the slow axis of the first waveplate being substantially perpendicular to the light transmission axis; determining a first waveplate extinction angle, the first waveplate extinction angle being an angle defined by the slow axis of the first waveplate and the polarization transmission direction of the polarizer, the first waveplate extinction angle being an angle at which extinction of the transmitted light occurs for the first waveplate; orienting the slow axis of the first waveplate at approximately forty-five degrees from the first waveplate extinction angle; interposing a second waveplate between the polarizer and the analyzer, the second waveplate being located along the light transmission axis, the second waveplate having a slow axis, the slow axis of the second waveplate being substantially perpendicular to the light transmission axis; determining a second waveplate extinction angle, the second waveplate extinction angle being an angle defined by the slow axis of the second waveplate and the polarization transmission direction of the polarizer, the second waveplate extinction angle being an angle at which extinction of the transmitted light occurs for the second waveplate; orienting the slow axis of the second waveplate at approximately forty-five degrees from the second waveplate extinction angle; recursively rotating the first waveplate about the light transmission axis, the first waveplate being recursively rotated in predefined angular increments, the recursive rotating of the first waveplate resulting in the slow axis of the first waveplate being at different angles with reference to the polarization transmission direction of the polarizer; and recursively rotating the analyzer about the light transmission axis to substantially minimize light being transmitted through the analyzer, the analyzer being recursively rotated in predefined angular increments, the analyzer being recursively rotated for each of the different angles of the slow axis of the first waveplate.