Influence of a two-photon saturable absorber on ultrashort pulse generation

It is shown theoretically that a two-photon absorber can be used in an ultrashort optical pulse generator to reduce the pulse duration and to increase the reproducibility. If rhodamine 6G is used as the two-photon absorber, the pulse shortening should be observed for a power density (in the case of a ruby laser) exceeding 16 GW/cm² but an even higher density would be required to improve the reproducibility. Experiments in which ruby laser radiation was focused in a two-photon absorber showed that such an absorber had a considerable influence on the generation of ultrashort pulses. The two-photon absorption cross section of rhodamine 6G agreed with the calculated value and with a value obtained earlier by a different method.