Enabling long-range exciton transport remains a significant challenge in artificial light-harvesting. This challenge stems, in part, from the lack of a characterization method that can follow an exciton on a sub-micron length scale with femtosecond temporal resolution. Access to these length and time scales will enable new insight into the design principles necessary to approach these challenges. We present optical resonance imaging (ORI), an optical analog of magnetic resonance imaging (MRI) that will enable widefield ultrafast microscopy with sub-diffraction-limited capabilities. ORI recovers an image from a heterodyne-detected, third-order, nonlinear photon-echo measurement. As opposed to traditional photon-echo measurements, the third pulse in the ORI pulse sequence has significant pulse-front tilt that produces a temporal gradient in the stimulated emission of a photon echo signal. We circumvent the diffraction limit of the optics by mapping the lateral spatial coordinate of the sample to the emission time of the signal. A coherent image can be resolved by using interferometric heterodyne detection to measure the precise arrival time of signal field on a detector. ORI thus maps space to time in analogy to how MRI maps space to energy. In addition, by scanning the times between pulses, exactly as in a typical third-order photon-echo measurement, we can extract spectral information analogously to 2D electronic spectroscopy. This allows us to correlate the spatial position of the exciton with its initial and final energies.<br/><br/>We discuss here the experimental implementation and widefield exciton imaging of thin films of dyes and nanocrystals. The current microscope achieves sub-5 μm resolution from a 100 μm diffraction limited spot and a sub-15 fs temporal resolution. The widefield nature enables rapid image acquisition without the use of raster scanning. We will also discuss how superresolution images are theoretically possible. This technique decouples resolution from the wavelength of light used, and the resolution is ultimately limited by the degree of pulse-front tilt and the temporal width of the photon echo. It will be shown that high-numerical-aperture optics can produce 240 nm resolution with 800 nm light.

Optical resonance imaging: An optical analog to MRI with sub-diffraction-limited capabilities

253rd National Meeting (2017)

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