Abstract

Laser eye protection filters exhibit a moisture shift phenomenon that must be carefully and accurately characterized. This phenomenon is the absorption of moisture in a thin film structure, causing an increase in refractive index for one or more of the materials. Once absorbed, some of the moisture is loosely bonded and can easily be driven off in vacuum or by low temperature heating. Some of the moisture is tightly bonded and can be driven off only with a high temperature bake. We have studied a series of testing techniques involving exposure of samples to vacuum, pressure, heat, and moisture or water to develop testing procedures to accurately evaluate their performance over the extremes of environmental exposure. The effect of loosely bonded moisture can be readily characterized by evaluation parts submerged in water and oven bakes at 80°C purging with dry gas. Characterization of tightly bonded moisture requires higher temperature to drive it out.

© 1992 Optical Society of America