# Coherent multi-heterodyne spectroscopy using acousto-optic frequency combs

## TL;DR

This paper introduces a novel acousto-optic frequency comb source for multi-heterodyne spectroscopy, capable of generating over 1500 coherent lines with reconfigurable spacing, enabling high-resolution and rapid molecular spectroscopy.

## Contribution

It presents a new acousto-optic frequency comb generation method that does not require non-linear broadening or external modulation, and demonstrates its application in high-resolution spectroscopy.

## Key findings

- Generated over 1500 coherent comb lines
- Achieved high frequency resolution of 500 kHz
- Demonstrated molecular spectroscopy with sub-millisecond time resolution

## Abstract

We propose and characterize experimentally a new source of optical frequency combs for performing multi-heterodyne spectrometry. This comb modality is based on a frequency shifting loop seeded with a CW monochromatic laser. The comb lines are generated by successive passes of the CW laser through an acousto-optic frequency shifter. We report the generation of frequency combs with more than 1500 mutually coherent lines, without resorting to non-linear broadening phenomena or external electronic modulation. The comb line spacing is easily reconfigurable from tens of MHz down to the kHz region. We first use a single acousto-optic frequency comb to conduct self-heterodyne interferometry with a high frequency resolution (500 kHz). By increasing the line spacing to 80 MHz, we demonstrate molecular spectroscopy on the sub-millisecond time scale. In order to reduce the detection bandwidth, we subsequently implement an acousto-optic dual-comb spectrometer with the aid of two mutually coherent frequency shifting loops. In each architecture, the potentiality of acousto-optic frequency combs for spectroscopy is validated by spectral measurements of hydrogen cyanide in the near-infrared region.

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Source: https://tomesphere.com/paper/1803.07618