Application of the nonlinear crystal SrB_4O_7 for ultrafast diagnostics converting to wavelengths as short as 125 nm

We used non-phase-matched second-harmonic generation (SHG) in the highly nonlinear but low-birefringence crystal SrB4O7 for temporal characterization (autocorrelation) of femtosecond UV pulses to convert these pulses to wavelengths as low as 125 nm, close to the transparency limit of SrB4O7. The sensitivity of this method was approximately 1 microJ at the fundamental for a repetition rate of 1 kHz. We also used SHG at longer wavelengths to estimate the three nonlinear coefficients of SrB4O7.