We can resolve multiple discrete features within a focal region of m spatial dimensions by first isolating each on the basis of n ≥ 1 unique optical characteristics and then measuring their relative spatial coordinates. The minimum acceptable separation between features depends on the point-spread function in the (m + n)d-dimensional space formed by the spatial coordinates and the optical parameters, whereas the absolute spatial resolution is determined by the accuracy to which the coordinates can be measured. Estimates of each suggest that near-field fluorescence excitation microscopy/spectroscopy with molecular sensitivity and spatial resolution is possible.
© 1995 Optical Society of America
E. Betzig, "Proposed method for molecular optical imaging," Opt. Lett. 20, 237-239 (1995)