Pulse broadening of deep ultraviolet femtosecond laser from second harmonic generation in KBe2BO3F2 crystal

Pulse broadening of deep ultraviolet (DUV) femtosecond (fs) laser in the KBe2BO3F2 (KBBF) crystal is experimentally investigated for the first time. Here, the 210 nm DUV fs light is produced by second harmonic generation (SHG) of a frequency doubled fs Ti:sapphire laser in a KBBF crystal with prism coupled device (KBBF–PCD). The DUV pulse width measurement is carried out with the approach of intensity cross-correlation based on frequency generation (DFG). Experiment result shows that the output 210 nm with 866 fs pulse width is significantly wider than its fundamental wave at 420 nm with 176 fs when the conversion efficiency is optimized. It also reveals that the estimated value by the previous method might underestimate the DUV pulse width because of neglecting the second and third-order nonlinear mechanisms in the KBBF–PCD.