Rapid and high-resolution chemical sensing using linear and nonlinear dual frequency comb spectroscopy

In recent years dual-comb spectroscopy (DCS) has emerged as a powerful method that can obtain linear absorption spectra of different analytes rapidly and with high spectral resolution. However, an important limitation of DCS is that the linear spectra obtained cannot distinguish between a three-level system with two resonant frequencies f₁ and f₂, and a mixture of two independent two-level systems with the same frequencies. This information is important for chemical sensing applications. In order to make this distinction, multidimensional coherent spectroscopy can be used but it requires long acquisition times and uses complex apparatus. Here we propose a different approach that uses a simple acquisition scheme and does not require the measurements of full multidimensional coherent spectra. This approach is based on photon echo spectroscopy and the dual-comb spectroscopy detection technique and enables the measurement of linear and nonlinear (photon-echo) signals from a sample of interest rapidly and with high spectral resolution. We show that the measured nonlinear signal contains spectroscopic information that, in conjunction with a linear signal, can be used to identify analytes in a mixture without measuring a full multidimensional coherent spectrum.