Preliminary results on the characterization and performances of ZBLAN fiber for infrared spectrographs

TL;DR

This paper presents preliminary findings on the use of ZBLAN fibers for infrared spectrographs, focusing on their impact on spectral quality and modal noise at high spectral resolution.

Contribution

It introduces the application of ZBLAN fibers in infrared spectrographs and reports initial results on their effects on spectral quality and modal noise.

Findings

Modal noise is more prominent at longer infrared wavelengths.

ZBLAN fibers influence the spectral quality in high-resolution infrared spectrographs.

Preliminary results suggest potential for fiber-fed infrared spectroscopy improvements.

Abstract

Present telescopes and future extremely large telescopes make use of fiber-fed spectrographs to observe at optical and infrared wavelengths. The use of fibers largely simplifies the interfacing of the spectrograph to the telescope. At a high spectral resolution (R>50,000) the fibers can be used to achieve very high spectral accuracy. GIANO is an infrared (0.95-2.5\mu m) high resolution (R=50,000) spectrometer[1] [2] [3] that was recently commissioned at the TNG telescope (La Palma). This instrument was designed and built for direct feeding from the telescope [4]. However, due to constraints imposed on the telescope interfacing during the pre-commissioning phase, it had to be positioned on the rotating building, far from the telescope focus. Therefore, a new interface to the telescope, based on IR-transmitting ZBLAN fibers with 85 \mu m core, was developed. In this article we report the first, preliminary results of the effects of these fibers on the quality of the recorded spectra with GIANO and with a similar spectrograph that we set-up in the laboratory. The effects can be primarily associated to modal-noise (MN) that, in GIANO, is much more evident than in optical spectrometers, because of the much longer wavelengths.