Multi-Dimensional Widefield Infrared-encoded Spontaneous Emission Microscopy: Distinguishing Chromophores by Ultrashort Infrared Pulses

Photoluminescence (PL) imaging has broad applications in visualizing biological activities, detecting chemical species, and characterizing materials. However, it is often limited by the total number of independently resolvable chromophores within the detection spectral windows, constraining the information encoded in an image. Here, we report a PL microscopy based on the nonlinear interactions between mid-infrared and visible excitations on matters, which we termed Multi-Dimensional Widefield Infrared-encoded Spontaneous Emission (MD-WISE) microscopy. MD-WISE microscopy demonstrates multiplexity in a three-dimensional space, by distinguishing chromophores that possess nearly identical emission spectra through three independent variables: the temporal delay between the infrared and the visible pulses, and the optical frequencies of the two pulses. More importantly, MD-WISE method operates at widefield imaging conditions, other than the confocal configuration adopted by most nonlinear optical microscopies which require focusing the optical beams tightly to reach high intensity for nonlinear interactions. MD-WISE microscopy is enabled by two mechanisms: 1. Modulating the optical absorption cross sections of molecular dyes by exciting specific vibrational functional groups; 2. Reducing the PL quantum yield of semiconductor nanocrystals through strong field ionization of excitons. By demonstrating the capacity of registering multi-dimensional information into PL images, MD-WISE microscopy has the potential of expanding the number of species and processes that can be simultaneously tracked in high-speed widefield imaging applications.