Birefringent member cell gap measurement method and instrument

摘要

A first polarizer and a second polarizer are located in an opposing relationship to each other on the optical axis of incident light with their polarization directions displaced from each other by a predetermined angle. A liquid crystal cell is arranged between the first polarizer and the second polarizer for rotation around the optical axis of the incident light. The incident light is introduced into the first polarizer while the liquid crystal cell is rotated. Transmission light, which is the incident light that has been transmitted successively through the first polarizer, the liquid crystal cell, and the second polarizer, is received by a photo-detector. The ratio between a variable component and a fixed component of the intensity of the transmission light is calculated. The cell gap of the liquid crystal cell is determined from the calculated ratio.