Optical design of a multi-channel narrow-band imager for Lyman ultraviolet observation of diffuse sources

This paper describes a novel optical design for a multi-channel narrow-band imager observing at the Lyman ultraviolet wavelengths. As one of the key instruments onboard the Census of Warm-Hot Intergalactic Medium, Accretion, and Feedback Explorer space mission, the imager is designed to map the neutral hydrogen Lyman-α line emissions from the intergalactic medium and nearby galaxies. The optical design features an instantaneous field of view (FOV) of 20 arc min in diameter and a moderate and adjustable spectral resolution of 500-2000. A highly dispersive monochromator system is used to split the incident light into several wavelength channels, each with a full-field imaging capability and adjustable bandwidth, and the ensuing imaging optics form the individual channel images on different areas of the same microchannel plate detector. Channel wavelengths are tunable and a continuous wavelength scanning across the entire band of interest is proposed, which yields spectrally resolved 3D images with moderate spectral resolutions.