Laser-induced behavior of BK7 mirror in a compound resonator on watt level DUV laser

Abstract

We experimentally present an acousto-optic Q-switched, side-pumped laser generating the watt-level deep-ultraviolet (DUV) output at 266 nm. A quasi-enhanced cavity, containing a BBO crystal as the fourth harmonic generator, was employed in the compact DUV laser system. A DUV laser with the average power of 1.08 W was achieved after careful alignment of the resonator. Our experimental results demonstrated that the DUV power was very sensitive to the misalignment of a cavity mirror. It was attributed to the thermal effect in BK7 mirror induced by high green power, by which the beam radius of green light was compressed in the compound resonator.

Improved beam profile of a 266 nm deep ultraviolet laser employing a multi-mirror-reflected cavity

“…According to [14], the walk-off angle in the BBO crystal is 85 mrad in the Φ direction. Reference [15] mentioned that the optical absorption may cause the thermal effect of the mirrors and then influence the characteristic of the output laser like average power and beam quality. But as seen in figure 5, the output power keeps increasing and the phenomenon is different from the description by [15], thus the thermal effect of mirrors can be ignored and it is proven that the distortion of the beam is mainly caused by the walk-off effect.…”

“…Reference [15] mentioned that the optical absorption may cause the thermal effect of the mirrors and then influence the characteristic of the output laser like average power and beam quality. But as seen in figure 5, the output power keeps increasing and the phenomenon is different from the description by [15], thus the thermal effect of mirrors can be ignored and it is proven that the distortion of the beam is mainly caused by the walk-off effect. In figure 6(b), the improvement of the profile is because with the limited 266 nm transmission (92%) of M6, about 8% of the output laser from mirror M5 is reflected back by mirror M6 and then reflected by M4 towards the output direction.…”