Tunable fiber-laser-based picosecond source for the ultraviolet

The development of ultrafast optical sources in the ultraviolet (UV) is of interest for variety of applications from quantum optics to biology. With the scarcity of solid-state lasers in the UV, nonlinear frequency conversion techniques represent a promising route for the generation of such source. In particular, intracavity frequency doubling of optical parametric oscillators (OPO) synchronously-pumped in the green can be an attractive approach to generate tunable high-repetition-rate ultrashort pulses in the UV. However, development of OPOs based on the well-established quasi-phase-matched nonlinear materials such as PPLN is challenging, when pumped in the green, due to photorefractive effect. On the other hand, MgO:sPPLT has proved to be an attractive alternative for green pumping [1]. At the same time, the birefringent nonlinear material, bismuth triborate, BiB₃O₆ (BIBO), possesses unique nonlinear optical properties for frequency conversion from the UV to IR [2]. It offers a relatively high nonlinearity (d_eff~3.2 pm/V) as compared to other widely used borate-based crystals such as LBO and BBO, making it an excellent nonlinear material for UV generation. Thus, the combination of green-synchronously-pumped OPO based on MgO:sPPLT together with internal frequency conversion in BIBO represents a versatile and practical approach to the development of tunable ultrafast sources in the UV.