Crystal-Configuration Considerations for Higher-Sensitivity Picosecond-Pulse SHG FROG
P. Šušnjar, Travis Jones, R. Trebino
Feb 5, 2020
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Journal
IEEE Journal of Quantum Electronics
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Key Takeaway Key Takeaway: A PPLN crystal is the most efficient nonlinear medium for SHG FROG, with a sensitivity of $2times 10-3$ (mW)2, making it ideal for picosecond pulse characterization.
Abstract
We experimentally compare a thick BIBO crystal, a walk-off compensating configuration of thin BBO crystals, and a thin PPLN crystal for the use as a nonlinear medium in SHG FROG, aiming for increased sensitivity required for complete pulse characterization of low-energy (below pJ) pulses a few picoseconds long at wavelengths near 1030 nm. We investigate the dependence of the spectral bandwidth of the frequency-doubled input ultrashort pulse and the conversion efficiency on focal-spot size in the nonlinear crystal. Both numerical and experimental results confirm an increase of the bandwidth with tighter focusing in a thick BIBO and a more-than-threefold increase of conversion efficiency compared to a thin BIBO crystal. A PPLN crystal is found to be the most efficient among the three, but very thin (< 0.3 mm) crystals would be required to extend the measurement capabilities of SHG FROG to sub-ps pulses. A SHG FROG using a PPLN crystal for characterization of picosecond pulse is demonstrated with a sensitivity of $2\times 10^{-3}$ (mW)2.