Spatially resolved dual-comb sensing with a single electro-optic modulator

Abstract

We demonstrate spatially resolved sensing by a novel approach that combines an infrared camera and a simplified dual-comb illumination arrangement. Specifically, our scheme employs a continuous-wave laser and only one electro-optic modulator to simultaneously create a pair of mutually coherent optical frequency combs, each one with a slightly different line spacing. The system operates by measuring this dual-comb spectrum from a sequence of acquired images, in order to recover the spectral response of every spatial point of a sample. Thanks to its excellent stability, our approach ensures integration times well in excess of 10 s. The result is an utterly simple multi-spectral imager, capable of resolving up to 127 independent comb lines (spectral channels) across 16 k individual spatial positions, with a digitization sampling rate close to 1 kHz. As a proof of concept, we measure spatial variations of the refractive index of a low-reflectivity etalon undergoing a heating process. This sensing unit has a great potential to work as a field-deployable system for the determination of the spatial distribution of external perturbations such as temperature or strain. We comprehensively discuss the current advantages and limitations of our sensing approach, as well as its further developments.