Calculate the molar concentration of the solution essential to obtain the value of 10 molecules per µm2. (For this calculation we suppose that the transfer of the dye molecules from solution to the sample surface by evaporation of the solvent is homogeneous on the whole wetted area.)
The sample is illuminated with the 543.5 nm-line of a green He-Ne laser. The excitation power is adjusted so that the illuminated area (100 nm in diameter) is hit by 3 · 1010 photons per second.