Four-level phase grating generated by combination of two binary gratings through coherent imaging

With the aim of steering as much incident light power in the +1 diffraction order as possible and suppressing the power in the -1 order, we generated an effective four-level grating by coherently imaging a 180 degrees binary-phase grating onto a 90 degrees phase grating. The periods of the gratings were well matched. The measured overall power fractions in the +1 and -1 orders were 54% and 2%, respectively.