Rotational relaxation and triplet-state effects in the cw dye laser

In a cw dye laser apparatus we measure first the fluorescence depolarization in the usual manner, and then the ratio of laser threshold pump powers for the laser polarization parallel and perpendicular to the linearly polarized pump source. From these two measurements we can obtain the important triplet-state parameter KT ≡ kSTτTσT/ σe, as well as the rotational relaxation time for the dye. For Rhodamine 6G in water with Triton X-100, we find KT=0.35 ± 0.02, while with Ammonyx-LO KT=0.25 ± 0.02. These additives also slow down the rotational relaxation of the dye molecule by more than an order of magnitude compared to common organic solvents.