Coherent Dual Comb Spectroscopy at High Signal to Noise

TL;DR

This paper presents a high-resolution, high signal-to-noise dual comb spectrometer capable of measuring complex molecular responses across a broad 9 THz bandwidth with exceptional accuracy and sensitivity.

Contribution

The authors design and demonstrate a coherent dual-comb spectrometer that achieves high spectral resolution and sensitivity over a wide bandwidth, advancing precision spectroscopy techniques.

Findings

Measured the complex response of hydrogen cyanide over 9 THz bandwidth.

Achieved a spectral resolution of 220 MHz with 41,000 resolution elements.

Attained a peak SNR of 4,000, enabling highly sensitive measurements.

Abstract

Two frequency combs can be used to measure the full complex response of a sample in a configuration which can be alternatively viewed as the equivalent of a dispersive Fourier transform spectrometer, infrared time domain spectrometer, or a multiheterodyne laser spectrometer. This dual comb spectrometer retains the frequency accuracy and resolution inherent to the comb sources. We discuss, in detail, the specific design of our coherent dual-comb spectrometer and demonstrate the potential of this technique by measuring the first overtone vibration of hydrogen cyanide, centered at 194 THz (1545 nm). We measure the fully normalized, complex response of the gas over a 9 THz bandwidth at 220 MHz frequency resolution yielding 41,000 resolution elements. The average spectral signal-to-noise ratio (SNR) is 2,500 for both the fractional absorption and the phase, with a peak SNR of 4,000 corresponding to a fractional absorption sensitivity of 0.025% and phase sensitivity of 250 microradians. As the spectral coverage of combs expands, this dual-comb spectroscopy could provide high frequency accuracy and resolution measurements of a complex sample response across a range of spectral regions.