High Efficiency Echelle Gratings for the Far Ultraviolet

TL;DR

This paper presents the fabrication and characterization of etched silicon echelle gratings optimized for the far ultraviolet, achieving significant efficiency improvements over traditional gratings, thereby enhancing future UV observatory performance.

Contribution

It introduces a novel silicon etching technique for creating high-efficiency FUV echelle gratings with sharp facets, surpassing traditional manufacturing limitations.

Findings

42% increase in peak order efficiency

83% decrease in interorder scatter

Analysis of residual efficiency sources

Abstract

Modern grating manufacturing techniques suffer from inherent issues that limit their peak efficiencies. The anisotropic etching of silicon facilitates the creation of custom gratings that have sharp and atomically smooth facets, directly addressing these issues. We describe work to fabricate and characterize etched silicon echelles optimized for the far ultraviolet (FUV; 90 - 180 nm) bandpass. We fabricate two echelles that have similar parameters to the mechanically ruled grating flown on the CHESS sounding rocket. We demonstrate a 42% increase in peak order efficiency and an 83% decrease in interorder scatter using these gratings. We also present analysis on where the remaining efficiency resides. These demonstrated FUV echelle improvements benefit the faint source sensitivity and high-resolution performance of future UV observatories.