NIRPS Front-End: Design, performance, and lessons learned

TL;DR

The paper discusses the design, on-sky performance, and lessons learned from the NIRPS Front-End, a high-precision, fiber-fed spectrograph for exoplanet detection using innovative few-mode fibers and adaptive optics.

Contribution

It introduces the NIRPS Front-End design and evaluates its performance, highlighting the use of few-mode fibers with adaptive optics for high-precision radial velocity measurements.

Findings

Successful on-sky performance demonstration

Effective coupling efficiency under poor seeing conditions

Identified challenges with modal noise in few-mode fibers

Abstract

NIRPS (Near Infra-Red Planet Searcher) is an AO-assisted and fiber-fed spectrograph for high precision radial velocity measurements in the YJH-bands. NIRPS also has the specificity to be an SCAO assisted instrument, enabling the use of few-mode fibers for the first time. This choice offers an excellent trade-off by allowing to design a compact cryogenic spectrograph, while maintaining a high coupling efficiency under bad seeing conditions and for faint stars. The main drawback resides in a much more important modal-noise, a problem that has to be tackled for allowing 1m/s precision radial velocity measurements. In this paper, we present the NIRPS Front-End: an overview of its design (opto-mechanics, control), its performance on-sky, as well as a few lessons learned along the way.