Externally Dispersed Interferometry for Precision Radial Velocimetry

TL;DR

Externally Dispersed Interferometry (EDI) combines a Michelson interferometer with a spectrograph to enhance Doppler velocimetry and high-resolution spectroscopy, enabling precise velocity measurements with lower resolution instruments.

Contribution

This paper introduces EDI as a novel technique that improves spectrograph performance by creating moire fringes, allowing high precision measurements with relaxed optical tolerances.

Findings

EDI produces moire fringes that shift with Doppler effects.

EDI enhances velocity measurement precision with lower resolution spectrographs.

The method is robust against spectrograph blurring and distortions.

Abstract

Externally Dispersed Interferometry (EDI) is the series combination of a fixed-delay field-widened Michelson interferometer with a dispersive spectrograph. This combination boosts the spectrograph performance for both Doppler velocimetry and high resolution spectroscopy. The interferometer creates a periodic spectral comb that multiplies against the input spectrum to create moire fringes, which are recorded in combination with the regular spectrum. The moire pattern shifts in phase in response to a Doppler shift. Moire patterns are broader than the underlying spectral features and more easily survive spectrograph blurring and common distortions. Thus, the EDI technique allows lower resolution spectrographs having relaxed optical tolerances (and therefore higher throughput) to return high precision velocity measurements, which otherwise would be imprecise for the spectrograph alone.