Broadband trapeziform multilayer dielectric grating for femtosecond pulse compressor: design, fabrication, and analysis

Abstract

Rectangular HfO2 grating fabrication is difficult, so a trapeziform multilayer dielectric pulse compression grating (PCG) has been designed using a genetic algorithm and the Fourier mode method. Simulation results show that a greater than 120 nm wavelength range multilayer dielectric grating (MDG) is obtained with a minus-first-order diffraction efficiency (DE) exceeding 95%. The bandwidth is 136 nm with the minus-first-order DE exceeding 90%. The trapeziform structure shows good tolerances for grating fabrication. The multilayer dielectric is deposited by e-beam evaporation, then the MDG is fabricated by reactive ion beam etching. A 128 nm bandwidth of the MDG for the transverse electric polarization with an efficiency exceeding 90% is obtained, and the maximum DE can reach up to 98.3%. The trapeziform MDG is an ideal PCG for chirped pulse amplification systems with high DE, broad bandwidth and good fabrication tolerances. Laser-induced damage thresholds of 0.53 J cm−2 under 40 fs pulses are experimentally reached with very high and uniform efficiency.