Experimental realization of Talbot array illumination for a 2-dimensional phase grating

摘要

We present the result of a multiple phase level Talbot array illuminator (TAI) based on two dimensional phase grating. The grating was fabricated on glass by a Deep Reactive Ion Etching (DRIE) system with optimized gas combination recipe. The opening ratio of the grating is ~0.71 with a phase step of n. The experimental study on Talbot array illuminations (TAI's) of this fabricated device in near-field region was carried out using a He-Ne laser. The TAI's were observed at the positions 2.81 mm, 8.59 mm, 14.28 mm, and 20.57 mm along the light propagation direction. The computer simulations of wave field distribution in near field region at different fractional Talbot distances have been generated. These simulated results are in reasonably good agreement with our experimental observed results. Our analysis on Talbot array illumination (TAI's) shows that the multiple harmonic phase modulations are transformed into intensity modulations at 1/8, 3/8, 5/8, and 7/8 fractional Talbot position. We have observed three different grating images, viz., attenuated, phase contrast, and diffraction contrast images. We also show the presence of a considerable amount of phase change at the edge of each phase sublevel that enhances the contrast of differential phase contrast imaging. Therefore, the phase contrast signal can be detected at a fractional position using single phase grating without the need of phase stepping.