Solarization effects in optical glass from UV to blue

Abstract

The decrease of transmittance due to electromagnetic radiation is called solarization. UV radiation generates color-centers in the glass that act as absorption sites. The spectral characteristic and level of solarization depends mainly on the composition. In microlithography applications optical glasses are used that are optimized for UV irradiations at 365 nm with minimized solarization effects. The solarization behavior of optical glass at SCHOTT is usually characterized using a Philips mercury high-pressure gas-discharge lamp type HOK-4/120 or a 365 nm LED. A method for solarization classification is described in the Japanese JOGIS standard 04-2019. Results are shown and discussed in comparison for several UV transmitting optical glasses and glasses used in i-line lithography applications. In recent years blue laser applications became more and more present in industrial and commercial applications. It was surprisingly found that high power blue laser irradiation also leads to solarization of optical glass. Therefore SCHOTT established a blue laser irradiation setup and spectral photometer measurement facility to characterize blue laser solarization effects on optical glass. Additionally stabilization strategies have been applied to stabilize optical glass against blue laser solarization. This paper discusses the actual status of the developments.