The infrared imaging spectrograph (IRIS) for TMT: spectrograph design

TL;DR

The IRIS spectrograph for TMT is a hybrid optical instrument designed to operate at the diffraction limit, combining lenslet and image slicer technologies to enable diverse high-resolution infrared observations.

Contribution

This paper introduces a novel hybrid spectrograph design that integrates two advanced IFS technologies for the TMT, optimizing performance and cost.

Findings

Design successfully combines lenslet and slicer IFS technologies.

Provides four different spatial scales for versatile observations.

Achieves high Strehl performance for detailed infrared imaging.

Abstract

The Infra-Red Imaging Spectrograph (IRIS) is one of the three first light instruments for the Thirty Meter Telescope (TMT) and is the only one to directly sample the diffraction limit. The instrument consists of a parallel imager and off-axis Integral Field Spectrograph (IFS) for optimum use of the near infrared (0.84um-2.4um) Adaptive Optics corrected focal surface. We present an overview of the IRIS spectrograph that is designed to probe a range of scientific targets from the dynamics and morphology of high-z galaxies to studying the atmospheres and surfaces of solar system objects, the latter requiring a narrow field and high Strehl performance. The IRIS spectrograph is a hybrid system consisting of two state of the art IFS technologies providing four plate scales (4mas, 9mas, 25mas, 50mas spaxel sizes). We present the design of the unique hybrid system that combines the power of a lenslet spectrograph and image slicer spectrograph in a configuration where major hardware is shared. The result is a powerful yet economical solution to what would otherwise require two separate 30m-class instruments.