From Waves to Photons
While quantized light was crucial to the development of quantum mechanics, uniting descriptions of the photoelectric eﬀect and blackbody radiation, it was the chemist G.N. Lewis who ﬁrst coined the term photon to describe the unit of electromagnetic energy. Physical chemists usually ensemble-average over the heterogeneous properties of individual photons, and our spectroscopic tools are typically built on a semi-classical description of light-matter interactions. While these wave descriptions of light are extremely powerful, (and allowed us to develop heterodyne and interferometric methods adapted radio spectroscopy) considering the properties of individual photons may allow for new forms of contrast as we monitor chemical reactions and energetic flow in materials.
We will develop heterodyne and inteferometric methods which combine intuition from nonlinear spectroscopies, to photon statistics. Photon correlation can answer fundamental questions about chemical and nanoscale heterogeneity. To accomplish this, I use detectors and electronics which can can time single photons, and use sophisticated post-processing (such as second an higher order correlations) to reveal spectroscopic observables, including lineshapes, spectral diffusion, and chemical kinetics. These techniques complement nonlinear spectroscopies and can be accomplished at low flux, on single molecules or dilute solutions, or even on weakly emissive materials.