Analyses of system error in the measurement of liquid crystal empty cell gap by means of interferometry

Influences on system error and relative standard deviation in the measurement of liquid crystal empty cell gap are analyzed in great detail. Great differences exist in system error and standard deviation among measuring methods. Momentum Scanning Interferometry (MSI) using the P wave can keep system error at a small level. ITO and PI layers are the main sources of system error, but their influence on MSI using the P wave is the least among different methods. Based on these analyses, an effective solution, MSI using sloping tiny beam, is presented. It can be used to measure the distribution of cell gap on line and is of high resolution, good repeatability, good stability and high precision.