Optical saturation measurements of fluorophores in solution with pulsed femtosecond excitation and two-dimensional CCD camera detection.

We present a new method for the measurement of saturation of the optical transition of fluorescent molecules in solution, which is based on detection with a CCD camera of a two-dimensional projection of the three-dimensional, spatially nonuniform fluorescence intensity distribution as generated in a bulk solution of the fluorophore by excitation with focused femtosecond optical pulses. Essential to the method is (a) a combination of information from a measurement in saturation and one not in saturation and (b) for the measurement in saturation, the simultaneous observation of both saturated and nonsaturated regions of the fluorescence intensity distribution. The experimental setup is straightforward and good agreement is found between the theory and the experimental data.