Optical design of LUVIS for SMEX

We are developing the design for the Lyman-Ultraviolet (LUV) Imaging Spectrograph, LUVIS to propose for a small explorer (SMEX) mission. LUVIS will provide true long slit (six arc minute) imaging spectroscopic capability with large spectral resolving power, R. Minimizing the number of optical components to the required minimum of three enables large spectral throughput. The design uses a two-mirror Cassegrain Ritchey-Chretien Optical Telescope assembly (OTA), a single optic Rowland-like spectrometer, and a windowless 50 x 127 mm curved microchannel plate (MCP). The design is optimized over the 102 to 140 nm spectral range providing spectral imaging at R ~ 20K in a single exposure. Lyman-β enhanced Al + LiF mirror and grating coatings with the LiF protected with an atomic layer deposition (ALD) fluoride encapsulating overcoat provide high throughput over that spectral range. Line-of-sight (LOS) jitter control utilizes time-tag photon arrival to compensate field position jitter by re-registering pixel location in post-processing as well as tip/tilt active control of the secondary mirror of the OTA. This paper will describe the design as well as some of the key design trades that defined the design.