A highly stable monolithic enhancement cavity for second harmonic generation in the ultraviolet

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Abstract
We present a highly stable bow-tie power enhancement cavity for critical second harmonic generation (SHG) into the UV using a Brewster-cut β-BaB2O4 (BBO) nonlinear crystal. The cavity geometry is suitable for all UV wavelengths reachable with BBO and can be modified to accommodate anti-reflection coated crystals, extending its applicability to the entire wavelength range accessible with non-linear frequency conversion. The cavity is length-stabilized using a fast general purpose digital PI controller based on the open source STEMlab 125-14 (formerly Red Pitaya) system acting on a mirror mounted on a fast piezo actuator. We observe 130 h uninterrupted operation without decay in output power at 313 nm. The robustness of the system has been confirmed by exposing it to accelerations of up to 1 g with less than 10% in-lock output power variations. Furthermore, the cavity can withstand 30 min of acceleration exposure at a level of 3 grms without substantial change in the SHG output power, demonstrating that the design is suitable for transportable setups.
Funding Information
  • Deutsche Forschungsgemeinschaft (CRC 1128 geo-Q, CRC 1227 DQ-mat)
  • Leibniz-Gemeinschaft (SAW-2013-FBH-3)

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