Cryogenic Volume-Phase Holograpic Grisms for MOIRCS

TL;DR

This paper reports the development and successful testing of cryogenic volume-phase holographic (VPH) grisms with ZnSe prisms for near-infrared observations in MOIRCS, demonstrating high efficiency and first astronomical application at cryogenic temperatures.

Contribution

It introduces the first use of cryogenic VPH grisms in astronomy, with fabrication, testing, and successful deployment in MOIRCS for infrared spectroscopy.

Findings

VPH grisms achieved 70-82% efficiency in laboratory tests.

Performance in telescope observations matched laboratory results.

First astronomical application of cryogenic VPH grisms.

Abstract

We have developed high dispersion VPH (volume phase holographic) grisms with zinc selenide (ZnSe) prisms for the cryogenic optical system of MOIRCS (Multi-Object near InfraRed Camera and Spectrograph) for Y-, J-, H- and K- band observations. We fabricated the VPH gratings using a hologram resin. After several heat cycles at between room temperature and 120 K, the VPH gratings were assembled to grisms by gluing with two ZnSe prisms. Several heat cycles were also carried out for the grisms before being installed into MOIRCS. We measured the efficiencies of the VPH grisms in a laboratory, and found them to be 70% - 82%. The performances obtained by observations of MOIRCS with the 8.2 m Subaru Telescope have been found to be very consistent with the results in the laboratory test. This is the first astronomical application of cryogenic VPH grisms.