A dual cavity Fabry-Perot device for high precision Doppler measurements in astronomy

TL;DR

This paper introduces a dual cavity Fabry-Perot interferometer designed for high-precision wavelength calibration and stability tracking in astronomical spectrographs, achieving sub-10$^{-10}$ m differential length stability for accurate Doppler measurements.

Contribution

It presents a novel dual cavity FPI design with optimized mounting to enhance stability and suppress length variations, enabling precise Doppler measurements in astronomy.

Findings

Achieved fractional length change of about 1.5×10$^{-12}$ with optimized mounting.

Identified conditions to suppress relative length variations below 10$^{-10}$ m.

Demonstrated potential for Doppler measurement accuracy at 10 cm/s.

Abstract

We propose a dual cavity Fabry-Perot interferometer as a wavelength calibrator and a stability tracking device for astronomical spectrograph. The FPI consists of two adjoining cavities engraved on a low expansion monoblock spacer. A low-finesse astro-cavity is intended for generating a uniform grid of reference lines to calibrate the spectrograph and a high-finesse lock-cavity is meant for tracking the stability of the reference lines using optical frequency standards. The differential length changes in two cavities due to temperature and vibration perturbations are quantitatively analyzed using finite element method. An optimized mounting geometry with fractional length changes $\Delta L/L \approx 1.5\times 10^{-12}$ is suggested. We also identify conditions necessary to suppress relative length variations between two cavities well below 10$^{-10}$~m, thus facilitating accurate dimension tracking and generation of stable reference spectra for Doppler measurement at 10 cms$^{-1}$ level.