Patent ID: 7719679

Claim:
A method of optically measuring a sample including a substance which at least has a first electronic state and a second electronic state, the second electronic state being an excited electronic state of the substance, the second electronic state having a limited lifetime, and the substance emitting photons out of its second state, the method comprising the steps of: selecting the substance in the sample from a group of substances having a lifetime of the second state of the substance in an order of magnitude of 1 ns; repeatedly temporally directing an electromagnetic signal having a repetition interval of time at least one area of the sample to transfer the substance in the at least one area of sample out of its first electronic state into its second electronic state; optimizing a value of the repetition interval of time of the signal with regard to a yield of photons from the substance, the optimized value being at least 0.1 μs with the lifetime of the second state having an order of magnitude of 1 ns; and detecting photons emitted by at least a part of the substance out of its second state; wherein the optimized value of the repetition interval of time of the signal is longer than a lifetime of a third state of the substance into which a considerable part of the substance in the sample is transferred due to the electromagnetic signal in a parasitic way, the lifetime of the third state being longer than the lifetime of the second state of the substance by at least one order of magnitude, and the substance being transferable with the electromagnetic signal out of its third state into a fourth state out of which the substance does neither return into the first state nor into the second state for an interval of time which is longer than the 100-fold of the lifetime of the third state.