Concept and optical design of the cross-disperser module for CRIRES+

TL;DR

This paper details the optical design of a new cross-disperser module for CRIRES+ that significantly enhances spectral coverage and maintains high resolution, enabling more efficient infrared astronomical observations.

Contribution

It introduces the optical design of the CRIRES+ cross-disperser module, allowing a >10-fold increase in spectral coverage while preserving high resolution and long slit capability.

Findings

>10 times increase in spectral coverage

Maintains high spectral resolution (up to R=100,000)

Supports observations of extended sources

Abstract

CRIRES, the ESO high resolution infrared spectrometer, is a unique instrument which allows astronomers to access a parameter space which up to now was largely uncharted. In its current setup, it consists of a single-order spectrograph providing long-slit, single-order spectroscopy with resolving power up to R=100,000 over a quite narrow spectral range. This has resulted in sub-optimal efficiency and use of telescope time for all the scientific programs requiring broad spectral coverage of compact objects (e.g. chemical abundances of stars and intergalactic medium, search and characterization of extra-solar planets). To overcome these limitations, a consortium was set-up for upgrading CRIRES to a cross-dispersed spectrometer, called CRIRES+. This paper presents the updated optical design of the crossdispersion module for CRIRES+. This new module can be mounted in place of the current pre-disperser unit. The new system yields a factor of >10 increase in simultaneous spectral coverage and maintains a quite long slit (10"), ideal for observations of extended sources and for precise sky-background subtraction.