Diffraction efficiency optimization of multilayer dielectric mirror-based gratings for 1030 nm femtosecond lasers

Abstract

Diffraction gratings that do not reach >99% diffraction efficiency (DE) are a major source of losses in chirped pulse amplification systems in current ultrashort pulse lasers. Here, we suggest an optimization route for diffraction gratings based on a commercially available, 1064 nm laser line high reflectivity (HR) multilayer-dielectric mirror. We modeled optical response of 1700lines/mm gratings in Littrow configuration imposed on this typical quarter wavelength-based stack structure. We demonstrate that theoretically DE of 99.995% at a single wavelength and >99% in 1003–1034 nm wavelength range can be achieved using the original dielectric mirror layer setup. The high DE spectral range could be broadened up to 992–1060 nm while still maintaining >99% DE, when the dielectric stack with a thinner topmost layer is considered. In both cases the diffraction grating grooves must span the two topmost layers, including a higher refractive index material, i.e. Nb2O5. Alternatively, >99% DE in 1009–1033 nm wavelength range can be also obtained using a thicker topmost layer. In this case, the grating groove spanning just the SiO2 layer is sufficient. However, twice as deep grooves and an accurate control of the filing factor is required. We show through numerical simulations that this structure is more sensitive to angular positioning error. The modelled electric field distributions showed reduced laser damage probability in the latter case. All investigated structures can sustain the bandwidth of sub-100 fs pulse length laser pulses. The proposed optimization route can serve as a guideline to design any diffraction grating based on commercially available dielectric mirrors.