The light flux of laser based digital projectors is constantly growing. Further, the setup gets more compact. This leads to increasing spatial dependent power densities inside color channel controlling optical systems of high-end laser cinema projectors. It was surprisingly found that high power blue laser irradiation leads to solarization of optical glass, resulting in a decrease of transmission over time. Therefore, SCHOTT started to develop blue laser solarization stable optical glass. A blue laser irradiation setup and spectral photometer measurement facility was established to characterize the solarization effect on optical glass. First very promising results of the development show that it is possible to significantly increase the stability of optical glass against blue laser solarization. This paper discusses the actual status of the development of blue solarization stable optical glass used for digital projection. Solarization results are shown as a function of time and wavelength. Additionally the intensity dependence and saturation of blue laser solarization is addressed.
Blue laser light has unique capabilities for material processing of copper gold or aluminium. The energy absorption efficiency at 450 nm in gold is orders of magnitude higher than the absorption at typical infrared wavelengths. Modern blue laser diodes enable very high energy densities. For focusing the laser beam usually fused silica optics are used. Fused silica is known for the very high solarization stability over wide range wavelengths but optical designs are limited to its specific optical position (refractive index and Abbe number). It would be beneficial for the optical design in terms of performance and flexibility to use optical glass for such applications. Only limited data is available on the solarization behavior of optical glass for high power laser radiation at 450 nm. This paper discusses the requirements on optical materials used for blue laser processing applications regarding long time stability aspects, showing recent results in the development of solarization stable glass optical glasses.
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