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Analysis of optical damage in germanium induced by a continuous wave laser.

To analyze optical damage of germanium (Ge) induced by a continuous wave (CW) laser, numerical and experimental studies were carried out. Temperature and solid-liquid phase transition with laser conditions were estimated by numerical simulation. In our experiments, we examined morphological changes with hillocks, material changes in the GeO2 layer by oxidation, and new crystal domains formed by recrystallization. The material damage process was explained. Transmittance reduction was also observed in the mid-infrared region. We confirmed that hillock formation, oxidation, and recrystallization through resolidification are critical factors in damaging the optical performance of Ge with a CW laser.