Broadband Two-Dimensional Infrared Spectroscopy with Signal Detection in Visible Range by Nonlinear Chirped-Pulse Upconversion

The paper presents a technique for broadband two-dimensional infrared spectroscopy with signal detection in visible range by nonlinear chirped-pulse upconversion. This approach helps to avoid direct measurement of the mid-infrared signal that requires cryogenic technology, and instead uses low-cost high-sensitivity multichannel silicon linear arrays. This leads to a reduction by two orders of magnitude of the measurement time of a single two-dimensional spectrum, which makes it possible to observe the fast dynamics of complex molecular compounds. The use of a quasi-phase-cycling achieved by sub-cycle delay modulation suppresses scattering background by almost two orders of magnitude and increases the measurement speed twice compared to optical chopping. Numerical simulation using the density matrix formalism and analysis of its evolution based on the solution of the Bloch–Redfield equation effectively reproduces the features of the two-dimensional infrared spectrum of inorganic octacarbonyl dicobalt compound.