Low-stray-light concave holographic gratings processed by combining the methods of photoresist hot-melting and oxygen-ion ashing.

The principal motivation for this paper is to reduce stray light and line roughness in concave holographic gratings (CHG). Compared with other previously reported line-smoothing grating techniques such as dynamic-exposure near-field holography, we successfully improve the line smoothing of CHG to approximately 10 nm from 2 nm. Our method uses optimization technologies and a combination of photoresist hot-melting (PHM) and oxygen-ion ashing (OIA), thereby improving the degree of stray light before and after optimization by one order of magnitude; the level processed by OIA, PHM, and OIA successively is ${7.85} \times {{10}^{ - 5}}$7.85×10. Combining the two technologies, we achieve lower stray light and straighter groove lines for the concave gratings, which is more effective, easy to implement, and incurs a low cost.