Abstract
We study numerically the second-harmonic generation (SHG) from subwavelength GaAs relief gratings with and without Au nano-stripes on the bottom of grating troughs. The SHG efficiency is calculated by finite element method as a function of grating amplitude, Au-stripes thickness, depth of trough for TE and TM polarized fundamental harmonic. Our results show that a deep subwavelength grating without Au stripes can be considered as a homogeneous film when the grating period is 3.5 times shorter than the wavelength. Such a grating with a certain amplitude enhances the SHG efficiency by about 20 times compared with the efficiency of a crystal with flat surface. The Au-stripes at the grating troughs significantly increase the electromagnetic field concentration in the crystal ridges of the grating due to plasmonic resonance. In this case, the SHG efficiency enhancement is more than 500 times, while the absolute value of SHG efficiency reaches 1.2 × 10−3% when the intensity of pump light is 1 GW/cm2.
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