Dual wavelengths monitoring for optical coatings.

A new monitoring method based on the use of dual wavelengths monitoring is proposed. Firstly, the sensitivity of each layer in an optical coating for the monitoring wavelength is calculated by admittance equations. Then two appropriate monitoring wavelengths are chosen to make sure that every layer has a sensitive terminal point. The thickness error of the layer can be compensated. For quarter-wave multilayer and nonquarter-wave multilayer optical coatings, the advantage of this new monitoring method has been demonstrated by both the theoretical analyses and experimental results.