Blue-laser solarization of optical glass

Abstract

The decrease of transmittance due to electromagnetic radiation is the so-called solarization. This effect is especially well documented for energetic UV light. Typically, these radiations generate color-centers in the glass that act as absorption sites whose spectral characteristic and magnitude depend strongly on the composition. In a recent work, we demonstrated that high power blue laser light, can also lead to solarization of optical glass. In recent years blue laser based solutions (wavelengths around 450 nm) became more and more present in industrial and commercial applications. Blue laser light has in deed unique capabilities for material processing of copper gold or aluminum. Due to their very high power densities modern blue laser diodes are also a technology of choice for illumination system of high performance digital projection, e.g. for cinema and event applications. Optical glasses are widely used in optical systems of blue light laser applications. From now on, these glasses must meet the stability requirements challenged by the steadily increasing power of blue laser, de facto understanding and mitigating this solarization phenomena is now a prime technical challenge. However, until recently only limited data were available on the specific solarization behavior of optical glass under high power blue laser radiation. To this end, SCHOTT has established a dedicated laser irradiation setup to thoroughly characterize blue laser solarization effects of optical glass. Strategies have been developed to achieve blue laser solarization stable glass for demanding applications. In the present work, we shows the stability of different optical glasses against blue laser solarization and discusses the results of the stabilization approach. Aspects like saturation level of the effect, power density and wavelength dependence are discussed for N-BK7 as an example.