Design of Multilayer Film Polarization-Independent Gratings

Laser beam combining technology currently plays an important role in optical systems. The combined beam grating is the most important realization component inside, so it is necessary to study the beam grating.Conventional metal gratings have high absorbance, and the damage threshold of metal gratings is usually not high.Multilayer dielectric film gratings are necessary for research because they have almost no absorption and high damage thresholds at the same time as high diffraction efficiency.Based on the theory of rigorous coupled wave (RCWA), a multilayer dielectric film grating model is established and a multilayer dielectric film grating with a center wavelength of 1053 nm is designed in the paper After a series of optimal design, the following results are obtained. Ta2O5 and SiO2 are selected as multi-layer material, and the multi-layer structure is S(HL)(boolean AND)12HTA.The groove density is 1480 lines/mm. The profile of grating grooves is rectangular.The duty cycle of surface relief structure is between 0.3-0.4, the groove depth is between 750-850nm, the sum of residual thickness and groove depth is between 930-1030nm.The -1st diffraction average efficiency of the grating is over 95% at the Littrow angle (51.2 degrees).Wavelength bandwidth greater than 40nm.The diffraction efficiency is the same as that of a metal grating.At the same time,the laser induced damage threshold can be improved.