Laser emission at 253.7  nm using a LaBGeO₅ and a Mg:LiTaO₃ crystal seeded by a 761.1  nm diode laser module

This paper presents single frequency emission at 253.7 nm using a miniaturized diode laser module at 761.1 nm together with a Mg:LiTaO₃ crystal and a LaBGeO₅ crystal in a single-pass configuration. The 761.1 nm pump laser consists of a MOPA with two tapered amplifiers whose emission is coherently combined to generate 5 W in a miniaturized diode laser module. From the pump beam, 1.1 W passes a periodically poled waveguide crystal of stoichiometric LiTaO₃ doped with MgO. The crystal produces a second harmonic beam with an optical power of 18 mW at 380.55 nm achieving a normalized conversion efficiency of 1.6 %/W. Both collinear beams are then used for single-pass sum frequency generation in a periodically poled LaBGeO₅ bulk crystal. Thus, an optical power of up to 5 µW at 253.7 nm was generated with a normalized conversion efficiency of 0.03%/W. The concept has great potential for a compact UVC laser in the near future.