Fast determination of saturation intensity and maximum emission rate by single-emitter imaging

We investigate the dependence of the spot size in single-emitter confocal imaging on the degree of saturation. We show that single-emitter spots are broadened and flattened significantly already at excitation intensities well below saturation. The resulting single-emitter spot shapes thus deviate significantly from the excitation point spread function. We show and support by Monte Carlo simulations that fitting of a single spot is sufficient to extract the saturation intensity and the maximum emission rate of a single emitter with high accuracy. Our results will be of interest in all areas of single-emitter studies. (c) 2006 Optical Society of America.