Efficient tunable UV pulse generation from a green pumped fs-OPCPA

High energy tunable ultrafast UV pulses are of great interest for a variety of applications. These pulses are also required for high repetition rate, fully coherent UV seeded free electron lasers [1] . In the absence of proper laser gain materials, optical parametric chirped pulse amplification (OPCPA) is considered as a foremost technique to generate high power tunable ultra-short laser pulses in various spectral ranges [2] . A typical example is the broadband green pumped OPCPA system driven by frequency doubled Ytterbium based chirped pulse laser amplifiers (CPA). The excellent power scalability of the OPCPAs allows generation of multi-millijoule, few femtosecond pulses with hundreds of watts of average power harnessing high energy and repetition rate commercially available CPA pump systems [3] . The absence of proper nonlinear crystals hinders operating OPCPAs directly in the UV spectral range. Therefore, frequency doubling, tippling or quadrupling of conventional OPCPAs are the usual techniques of generating tunable UV pulses. However, these schemes suffer from the strong two-photon absorption, narrow phase matching bandwidth, and non-linear phase transfer to UV range. As a consequence, for ultra-short pulses the maximum conversion efficiency of such schemes is typically limited to below 10%, and usually accompanied by pulse compression complications.