Contaminant and defect analysis of optical surfaces by infrared laser induced desorption

Abstract

Infrared laser induced desorption (LID) has been demonstrated for water and other contaminants on nominally transparent substrates. For the samples measured to date, the LID is defect dominated for both small (120 μm) and large (380 μm) spot sizes. For the larger spot sizes, the data for multiple irradiations of the same site (N/1) can be explained using a simple defect model. The surface damage threshold of these materials correlates with the measured LID fluence, i.e., samples and sites with high contaminant fluences damage at low thresholds. Laser cleaned surfaces of CaF2, BaF2, and NaCl which were dosed with H2O at approximately −100 °C showed no evidence of readsorbed water on subsequent LID testing, indicating a passivation of the surface.