Influence of duty cycle on near-field diffraction of high-density gratings

Near-field intensity distributions of high-density amplitude gratings with period d=2.3λ and different duty cycles illuminated by TE and TM polarized waves are simulated by using the finite-difference time-domain method. Numerical results show that intensity distributions of in the grooves change differently when duty cycle varies for TE and TM polarizations. As duty cycle increases, peak intensity in the middle of the first bright stripes and its locations change obviously. The main reason of location variation of the first bright stripes is the variation of the phase difference between the ±2^nd orders and the 0^th order, which is verified by using rigorous coupled-wave analysis. The investigation of influence of duty cycle on near-field diffraction of high-density gratings should be helpful for practical applications of high-density gratings.