A 12.5 GHz-Spaced Optical Frequency Comb Spanning >400 nm for near-Infrared Astronomical Spectrograph Calibration

TL;DR

This paper presents a highly stable, broad-spectrum optical frequency comb with 12.5 GHz spacing, suitable for precise near-infrared astronomical spectrograph calibration, achieving sub-meter-per-second radial velocity measurement accuracy.

Contribution

It introduces a novel 12.5 GHz-spaced comb with extended wavelength coverage and detailed stability analysis, advancing spectrograph calibration capabilities.

Findings

Wavelength coverage from 1380 nm to 1820 nm achieved

Sidemode suppression between 20 dB and 45 dB

Optical linewidth approximately 350 kHz at 1550 nm

Abstract

A 12.5 GHz-spaced optical frequency comb locked to a Global Positioning disciplined oscillator for near-IR spectrograph calibration is presented. The comb is generated via filtering a 250 MHz-spaced comb. Subsequency nonlinear broadening of the 12.5 GHz comb extends the wavelength range to cover 1380 nm to 1820 nm, providing complete coverage over the H-band transmission widow of Earth's atmosphere. Finite suppression of spurious sidemodes, optical linewidth and instability of the comb have been examined to estmiate potential wavelength biases in spectrograph calibration. Sidemode suppression varies between 20 db and 45 dB, and the optical linewidth is ~350 kHz at 1550 nm. The comb frequency uncertainty is bounded by +/- 30 kHz (corresponding to a radial velocity of +/- 5 cm/s), limited by the Global Positioning System disciplined oscillator reference. These results indicate this comb can readily support radial velocity measurements below 1 m/s in the near-IR.