Non-degrading CW UV generation in β-barium borate at 257 nm using an elliptical focusing enhancement cavity

Abstract

With a combination of an elevated temperature for the β-barium borate (BBO) crystal and an elliptical focusing cavity we succeeded in eliminating the degradation in BBO during second harmonic generation into the ultraviolet (UV). We were capable of generating over 600 mW continuous-wave UV light at 257 nm with an off-the-shelf crystal for over 8 h without any sign of degradation. Our results indicate that the degradation is caused by color centers generated by two-photon absorption (TPA) strongly increasing the absorption of the fundamental radiation. While the higher crystal temperature reduces the TPA coefficient and the life time of the color centers, elliptical focusing strongly reduces the peak irradiance of the fundamental and thus its absorption.

On identifying critical parameters in an amplification without inversion setup in mercury *

“…The degradation in BBO can be overcome by an elliptical focusing cavity as reported in [22]. Elliptical focusing inside the crystal leads to much smaller peak intensities while still maintaining a high conversion efficiency.…”

“…Elliptical focusing inside the crystal leads to much smaller peak intensities while still maintaining a high conversion efficiency. By using a design process employing evolutionary algorithms described in [23], a novel enhancement cavity was designed that allowed maintaining high UV powers over hours of operation [22]. We were able to utilize the very same design in our experiment.…”

“…We were able to utilize the very same design in our experiment. Therefore, we refer to previous publications [22,23] for further details about the enhancement cavity.…”