Crystal-Configuration Considerations for Higher-Sensitivity Picosecond-Pulse SHG FROG

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 ×10 −3 (mW) 2 .

High-Sensitivity, Simple Frequency-Resolved-Optical-Gating Device

“…Based on these measurements, we estimate the spot size using the 100mm lens to be 27µm±2µm. Using the methods discussed in [26] and [27] we estimate in Fig. 3(a) the spectral resolution and in Fig.…”