# Broadband Dual Frequency Comb Spectroscopy in a Rapid Compression Machine

## TL;DR

This paper demonstrates fiber dual frequency comb spectroscopy for broadband, high-resolution measurements in a rapid compression machine, enabling in situ diagnostics of combustion processes with microsecond temporal resolution.

## Contribution

It introduces an apodization technique to enhance SNR in dual comb spectroscopy, allowing broadband measurements at combustion-relevant timescales in a rapid compression machine.

## Key findings

- Achieved 704 microsecond time resolution during compression
- Measured absorption spectra across 24345 wavelength elements
- Fitted temperature data agrees with adiabatic model

## Abstract

We demonstrate fiber mode-locked dual frequency comb spectroscopy for broadband, high resolution measurements in a rapid compression machine (RCM). We apply an apodization technique to improve the short-term signal-to-noise-ratio (SNR), which enables broadband spectroscopy at combustion-relevant timescales. We measure the absorption on 24345 individual wavelength elements (comb teeth) between 5967 and 6133 cm-1 at 704 microsecond time resolution during a 12-ms compression of a CH4-N2 mixture. We discuss the effect of the apodization technique on the absorption spectra, and apply an identical effect to the spectral model during fitting to recover the mixture temperature. The fitted temperature is compared against an adiabatic model, and found to be in good agreement with expected trends. This work demonstrates the potential of DCS to be used as an in situ diagnostic tool for broadband, high resolution, measurements in engine-like environments.

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Source: https://tomesphere.com/paper/1901.11059