Broadband dual-comb hyperspectral imaging and adaptable spectroscopy with programmable frequency combs

TL;DR

This paper introduces a programmable dual-comb spectroscopy platform that dynamically adjusts spectral resolution in real-time without deadtime penalties, enabling fast, adaptable hyperspectral imaging with high signal-to-noise ratio.

Contribution

The authors develop a free-form dual-comb spectroscopy system that allows real-time, penalty-free resolution tuning and hyperspectral imaging, surpassing traditional methods in flexibility and efficiency.

Findings

Spectral resolution varied from 160 MHz to 822 GHz.

Signal-to-noise ratio increases linearly with resolution, up to 5000x.

Achieved 20 Hz hyperspectral movies over 10 THz spectral range.

Abstract

We explore the advantages of a free-form dual-comb spectroscopy (DCS) platform based on time-programmable frequency combs for real-time, penalty-free apodized scanning. In traditional DCS, the fundamental spectral resolution, which equals the comb repetition rate, can be excessively fine for many applications. While the fine resolution is not itself problematic, it comes with the penalty of excess acquisition time. Post-processing apodization (windowing) can be applied to tailor the resolution to the sample, but only with a deadtime penalty proportional to the degree of apodization. The excess acquisition time remains. With free-form DCS, this deadtime is avoided by programming a real-time apodization pattern that dynamically reverses the pulse periods between the dual frequency combs. In this way, one can tailor the spectrometer's resolution and update rate to different applications without penalty. We show operation of a free-form DCS system where the spectral resolution is varied from the intrinsic fine resolution of 160 MHz up to 822 GHz by applying tailored real-time apodization. Because there is no deadtime penalty, the spectral signal-to-noise ratio increases linearly with resolution by 5000x over this range, as opposed to the square root increase observed for postprocessing apodization in traditional DCS. We explore the flexibility to change resolution and update rate to perform hyperspectral imaging at slow camera frame rates, where the penalty-free apodization allows for optimal use of each frame. We obtain dual-comb hyperspectral movies at a 20 Hz spectrum update rate with broad optical spectral coverage of over 10 THz.