Theoretical and experimental studies of tunable ultraviolet-blue femtosecond pulses in a 405-nm pumped type I β-BaB_2O_4 noncollinear optical parametric amplifier and cascading sum-frequency generation

Abstract

Femtosecond laser pulses that are tunable from 380 to 460 nm were directly generated from a 405-nm-pumped type I β-BaB2O4 noncollinear optical parametric amplifier (NOPA). A white-light supercontinuum from a CaF2 plate excited by 810-nm pulses was seeded into the NOPA. A theoretical analysis showed that the near-UV-to-blue radiation generated is attributable to cascaded sum-frequency generation (SFG) of the output of the NOPA and the residual fundamental beam at 810 nm. One can tune the blue–UV light by either changing the orientation of the NOPA crystal or adjusting the angle between the pump and the seeding pulse. The optical conversion efficiency from the 405-nm pump to the tunable SFG radiation is more than 5%.