Optical design for Subaru Nasmyth Beam Switcher

Subaru Nasmyth Beam-Switcher (SNBS) is an instrument designed for Nasmyth platform at Subaru telescope. It is a relay optics system which switches the light downstream of AO188 and LTAO to multiple instruments and allow multiple instruments work simultaneously with Subaru Coronagraphic Extreme Adaptive Optics system(SCExAO). The design has been completed and is now in building phase. The instrument working wavelength range is from 0.5 mu m to 5.3 mu m with field of view of 75 arcsecs in diameter. In this paper, we present its optical design and performance at different exit bays with various adaptive optics(AO) configurations. The wavefront at SCExAO bay is investigated. Tolerance and thermal performance of the switcher is also presented.