Coherent, multi-heterodyne spectroscopy using stabilized optical frequency combs

TL;DR

This paper demonstrates a method using stabilized optical frequency combs for rapid, high-precision multi-heterodyne spectroscopy that captures the full complex spectrum of a molecular gas across a wide bandwidth.

Contribution

It introduces a technique that measures the full complex spectrum of molecular gases with high accuracy using stabilized optical frequency combs and multi-heterodyne detection.

Findings

Measured 155,000 comb lines across 1495-1620 nm range

Achieved phase spectrum consistent with Kramers-Kronig relations

Provided rapid, wideband complex spectral measurements

Abstract

The broadband, coherent nature of narrow-linewidth fiber frequency combs is exploited to measure the full complex spectrum of a molecular gas through multi-heterodyne spectroscopy. We measure the absorption and phase shift experienced by each of 155,000 individual frequency comb lines, spaced by 100 MHz and spanning from 1495 nm to 1620 nm, after passing through a hydrogen cyanide gas. The measured phase spectrum agrees with Kramers-Kronig transformation of the absorption spectrum. This technique can provide a full complex spectrum rapidly, over wide bandwidths, and with hertz-level accuracy.