Adaptive optics for high resolution spectroscopy: A direct application with the future NIRPS spectrograph

TL;DR

This paper presents an adaptive optics system designed for the NIRPS spectrograph to improve high-resolution near-infrared spectroscopy by reducing instrument size and cost, enabling better radial velocity measurements.

Contribution

It introduces a novel AO module for the NIRPS spectrograph that efficiently feeds multi-mode fibers, enhancing spectral resolution and stability for faint M-type stars.

Findings

AO system achieves 50% energy coupling into 0.4" fiber for I=12 stars

Designed AO system operates effectively in 0.98-1.8 μm range

Potential to reduce spectrograph size and improve stability

Abstract

Radial velocity instruments require high spectral resolution and extreme thermo-mecanical stability, even more difficult to achieve in near-infra red (NIR) where the spectrograph has to be cooled down. For a seeing-limited spectrograph, the price of high spectral resolution is an increased instrument volume, proportional to the diameter of the primary mirror. A way to control the size, cost, and stability of radial velocity spectrographs is to reduce the beam optical etendue thanks to an Adaptive Optics (AO) system. While AO has revolutionized the field of high angular resolution and high contrast imaging during the last 20 years, it has not yet been (successfully) used as a way to control spectrographs size, especially in the field of radial velocities. In this work we present the AO module of the future NIRPS spectrograph for the ESO 3.6 m telescope, that will be feed with multi-mode fibers. We converge to an AO system using a Shack-Hartmann wavefront sensor with 14x14 subapertures, able to feed 50% of the energy into a 0.4" fiber in the range of 0.98 to 1.8 $\mu m$ for M-type stars as faint as I=12.