The inventive method for optically measuring a sample consists in temporarily repeatedly transmitting an electromagnetic signal (2) to the sample in such a way that a substance contained in the sample is transferred from a first electronic state (1) into a second electronic state (3), wherein at least one part of said substance in the second state (3) emits photons which are used for carrying out the optical measurement of the sample, the signal (2) is transmitted to the same sample area at a certain repetition interval and said repetition interval of the signal (2) is adjusted with a lifetime of the second state (3) of the substance having an order of magnitude of 1 ns on a value of at least 0.1 .mu.s which is optimized with respect to photon yield from the substance.