Crosscorrelation measurements of ultrashort visible pulses: comparison between nonlinear crystals and SiC photodiodes

Crosscorrelation (CC) measurements of tunable sub-20 fs visible pulses from noncollinearly phase matched optical parametric amplifiers are reported. It is found that even 25 and 100 μm thick BBO crystals used as the nonlinear medium possess too small an acceptance bandwidth. For vanishing chirp of the pulses or linear chirp of the same sign, the resulting error in the observed CC width is not very severe, however, for opposing chirp errors larger than a factor of 2 are demonstrated. In contrast, measurements utilizing two-photon photoconductivity in SiC photodiodes are found to be simple and very reliable. The SiC photodiode is well suited for both interferometric autocorrelation measurements on the 10 fs time scale and for CC measurements in the visible.