Few-cycle optical pulse characterization under phase-mismatching

The phase-matching bandwidth of nonlinear crystal is of great significance in ultrashort laser pulse characterization. In order to satisfy the phase-matching bandwidth, ultrathin nonlinear crystals are generally required. However, the significantly reduced conversion efficiency, as well as the machining difficulties, limits its applications. Here, we show that sufficient spectrum bandwidth response can be achieved for a thick crystal when the phase-matching wavelength is tuned outside of the spectral window of the measured pulse. By applying this phenomenon to a single-shot second-harmonic generation frequency resolved optical gating (SHG-FROG) device, we successfully characterized a few-cycle pulse using a 150 mu m beta-barium borate (BBO) crystal. The accuracy of the method was verified by comparing the conventional pulse retrieving approach with a 5 mu m BBO crystal, which has a sufficient phase-matching bandwidth. (C) 2021 Optical Society of America

Automated summary

This study shows that a thick crystal can achieve sufficient spectrum bandwidth response when the phase-matching wavelength is tuned outside of the spectral window of the measured pulse, enabling successful characterization of ultrashort laser pulses. The accuracy of the method was confirmed by comparing it with traditional pulse retrieval approaches.