Passive mode-locking of a Coumarin dye laser from 505–520 nm using DOCI as the saturable absorber

We report the passive mode-locking of a flash lamp pumped dye laser operating with a mixture of Coumarin 500^F and Coumarin 504 lasing dyes using DOCI (3,3'-diethyl oxacarbocyanine iodide) as the saturable absorber. We also suggest the formation of a transient photoisomer to be responsible for the mode-locking obtained with DOCI at long wavelengths, where the normal form has a very low absorption cross section.