Optimization and tolerancing of highly dispersive multilayer gratings for laser applications

Abstract

There are several applications for diffraction gratings in laser physics like frequency stabilization, wavelength tuning and temporal pulse shaping. Especially the growing market for femtosecond lasers with increasing pulse energies and peak powers boosts the requirement for highly dispersive diffraction gratings with diffraction efficiencies close to unity and highest damage thresholds imposing the use of purely dielectric materials. These advanced requirements also give rise to new challenges for the grating design. Classical design approaches like gold-coated reflection gratings or monolithic transmission gratings are becoming insufficient. Different approaches utilize dielectric multilayer coatings in conjunction with gratings to achieve high transmission or reflection efficiencies together with high damage thresholds. However, to realize a reasonable and robust design, the optimization of the grating and the multilayer stack has to be completed in one step using rigorous methods because interference of multiply diffracted orders contributes to the overall diffraction efficiencies. Moreover, to make these designs feasible for manufacturing, also a tolerancing is necessary. In our contribution, we present self-developed design tools for multilayer gratings where the optimization of both, grating and multilayer stack are combined in one step using Rigorous Coupled Wave Analysis and standard local and global optimization methods like interior point and genetic algorithms. Moreover, a tolerancing routine is included. New designs are presented for multilayer dielectric reflection and transmission gratings based on our approach, including considerations on tolerancing. Gratings etched through multiple layers are proposed to achieve higher bandwidths with top hat diffraction efficiencies.