Influence of two typical defects on the near-field optical properties of multilayer dielectric compression gratings.

Internal electric-field enhancement is critical for the laser-induced damage properties of multilayer dielectric compression gratings (MDG) in high-energy laser systems. Due to the complex fabrication processes of MDGs, such as coating, interference lithography, etching, and cleaning, different kinds of defects in multilayers or profiles on MDG surfaces can't be practically avoided. Combined with a scanning electron microscope of some MDG samples, line-absence and added node seem to be two typical defects, according to which two defective MDG models are established, and numerical calculations are performed. From simulation results, the defect period and defect depth has little effect on the spectral response of the optical elements. However, they may produce large changes of internal electric-field distribution on the grating surface and even in multilayer structures, thus decreasing the damage threshold of MDG. To obtain a better understanding of the dependence of the internal electric-field enhancement on these defects, this work is focused on the near-field distributions of defective MDGs using the Fourier model method.