Photon-Correlation Fourier Spectroscopy on CdSe Nanocrystals

The emission spectrum of a single emitter can be artificially widened and blurred due to fluctuations in emission energy, i.e. spectral diffusion. ~This spectral diffusion can be much more rapid than the time required to collect sufficient photons to measure a spectrum. ~We use a new method, Photon-Correlation Fourier Spectroscopy (PCFS), to ``freeze'' spectral diffusion and obtain spectral information of single CdSe nanocrystals on timescales comparable to the lifetime of the emitter.~ This method cross-correlates the two outputs of a Michelson interferometer, providing a histogram of frequency shifts between two photons separated by a given amount of time. ~~We apply PCFS to single nanocrystals in a confocal geometry.~ We also combine PCFS with Fluorescence Correlation Spectroscopy (FCS) to resolve single nanocrystal linewidths from a solution of nanocrystals diffusing under a microscope objective.~