Quasi-Talbot effect of the high-density grating in near field.

On the basis of the finite-difference time-domain technique, the diffraction of the high-density grating in the near field is developed, and the gray-scale pattern of the diffraction intensity distribution of a one-dimensional grating is presented. A detailed analysis shows that the near-field diffraction of the grating is the result of the diffraction of a single slit, the interference of two evanescent waves from neighboring slits, and the interference of the homogeneous waves from the slits. Through many numerical calculations, the condition for obtaining the quasi-Talbot imaging of the grating in the near field is explored, i.e., the period of the grating d is larger than the incident wavelength lambda but smaller than 4lambda. The influence of the opening ratio of the grating on the quasi-Talbot imaging of the grating in the near field is also discussed. This study of the near-field diffraction of the high-density grating may be helpful for understanding the diffraction characteristics of subwavelength structures, and the quasi-Talbot imaging of the high-density grating will contribute to the application of the grating in near-field photolithography.