Chirped volume Bragg gratings with nonlinear periods generated by two-cylindrical-beam holographic recording for robust ultrashort pulse compression

Chirped volume Bragg gratings (CVBGs) recorded in photo-thermo-refractive (PTR) glass are attractive compact pulse compressors for ultrafast laser systems.Conventional calculations assume a linear grating period and execute single-parameter analysis, limiting prediction of the coupled diffraction and dispersive responses generated by interference between converging and diverging cylindrical beams.Here, we first propose the resulting nonlinear grating period distribution in CVBGs and combine it with a multi-parameter coupled analysis.A PTR-glass CVBG compressor designed and fabricated for a 1030 nm ultrafast fiber laser exhibits an average relative diffraction efficiency of 85.2% over 1025.92-1033.48nm and compresses a 638 ps pulse to 6.98 ps at 3.5 W.An inverse temporal reconstruction shows that the nonlinear-period model reproduces the measured pulse with a 73.1% lower normalized root-mean-square deviation (NRMSD) than that of the linear-period model.The CVBG maintains stable compressed output power and thermal response during two hours of operation.This work removes a key obstacle limiting CVBGs in high-power ultrafast lasers.