Far Ultraviolet Scatter Performance from Holographic Gratings

摘要

We present deep scatter measurements on a sinusoidal profile, high groove density, holographically ruled, large format grating. With long exposures and a low-noise detector, we were able to measure scatter at levels of 1 * 10~(-6)/Ly αm at 100 nm. The result has potential impacts in the prospect of high sensitivity measurements of very faint objects at FUV wavelengths. Any instrument sensitive to hydrogen Lyman a, a bright geo-coronal airglow line, must control the scatter to make astrophysically significant measurements. Measurements of very faint emission line source - particularly ones that do not have known redshifts (i.e. wavelength solution), Lyman a scatter may be the dominant source of error. Therefore, characterization of the actual value of scatter is crucial to the success of future missions that will use diffraction-based measures for detecting very faint targets.