echelon grating

echelon-grating的词性：
n.（名词）

1. A diffraction grating made of parallel glass plates, each of which extends slightly beyond the next, used to examine extremely fine structures.
梯状光栅：用来检查极小结构的衍射光栅，由平行的玻璃片组成，每块玻璃片都比邻近一块长出一点