Modal Noise Mitigation through Fiber Agitation for Fiber-fed Radial Velocity Spectrographs

Abstract

Optical fiber modal noise is a limiting factor for high precision spectroscopy signal-to-noise in the near-infrared and visible. Unabated, especially when using highly coherent light sources for wavelength calibration, modal noise can induce radial velocity (RV) errors that hinder the discovery of low-mass (and potentially Earth-like) planets. Previous research in this field has found sufficient modal noise mitigation through the use of an integrating sphere, but this requires extremely bright light sources, a luxury not necessarily afforded by the next generation of high-resolution optical spectrographs. Otherwise, mechanical agitation, which "mixes" the fiber's modal patterns and allows the noise to be averaged over minutes-long exposures, provides some noise reduction but the exact mechanism behind improvement in signal-to-noise and RV drift has not been fully explored or optimized by the community. Therefore, we have filled out the parameter space of modal noise agitation techniques in order to better understand agitation's contribution to mitigating modal noise and to discover a better method for agitating fibers. We find that modal noise is best suppressed by the quasi-chaotic motion of two high-amplitude agitators oscillating with varying phase for fibers with large core diameters and low azimuthal symmetry. This work has subsequently influenced the design of a fiber agitator, to be installed with the EXtreme PREcision Spectrograph, that we estimate will reduce modal-noise-induced RV error to less than 3.2 cm/s.

arXiv commentAccepted by The Astrophysical Journal

References in corpus (15)

• State of the Field: Extreme Precision Radial Velocities
• Multimode optical fiber based spectrometers
• EXPRES: A Next Generation RV Spectrograph in the Search for Earth-like Worlds
• An efficient, compact, and versatile fiber double scrambler for high precision radial velocity instruments
• Suppression of Fiber Modal Noise Induced Radial Velocity Errors for Bright Emission-Line Calibration Sources
• iLocater: A Diffraction-limited Doppler Spectrometer for the Large Binocular Telescope
• Modal noise prediction in fibre-spectroscopy I: Visibility and the coherent model
• Optical fiber modal noise in the 0.8 to 1.5 micron region and implications for near infrared precision radial velocity measurements
• 'Modal-noise' in single-mode fibers: A cautionary note for high precision radial velocity instruments
• Precision near-infrared radial velocity instrumentation II: Non-Circular Core Fiber Scrambler
• Preliminary results on the characterization and performances of ZBLAN fiber for infrared spectrographs
• Fiber scrambling for high-resolution spectrographs. II. A double fiber scrambler for Keck Observatory
• Optimal non-circular fiber geometries for image scrambling in high-resolution spectrographs
• Comparing modal noise and FRD of circular and non-circular cross- section fibres
• The Habitable-zone Planet Finder Calibration System

Cited by in corpus (9)

• Performance Verification of the EXtreme PREcision Spectrograph
• EXPRES I. HD~3651 an Ideal RV Benchmark
• Experimental characterization of modal noise in multimode fibers for astronomical spectrometers
• Excalibur: A Non-Parametric, Hierarchical Wavelength-Calibration Method for a Precision Spectrograph
• The Measured Impact of Chromatic Atmospheric Effects on Barycentric Corrections: Results from the EXtreme PREcision Spectrograph
• High Repetition-Rate Femtosecond Stimulated Raman Spectroscopy with Fast Acquisition
• A Harsh Test of Far-Field Scrambling with the Habitable Zone Planet Finder and the Hobby Eberly Telescope
• Modal noise mitigation for high-precision spectroscopy using a photonic reformatter
• A small actively-controlled high-resolution spectrograph based on off-the-shelf components