Laser dye stability. Part 5

Photodegradation parameters that relate bleaching and absorption at the lasing wavelength λ_l have been examined for over 30 different coumarin and quinolone laser dyes in a number of solvents. Quinolone dyes were found to bleach faster than the coumarin dyes. The effect of chemical substituents was found to affect bleaching of the coumarin dyes only to a small (20%) extent in ethanol. The major effect of chemical substituents was in the conversion of a dye to products absorbing at λ_l. Effects of solvent, cover gas, and changes in fluorescent quantum yields are discussed. Of particular interest is the photodegradation parameterA, the ratio of the percent absorption at λ_l to the total input energy per dm³. Combined with τ, the total input energy per dm³ required for a laser to reach half its original intensity, it was found thatAτ=1.2±0.9 for all of the dyes independent of dye concentration in all of the solvents tested. It appears that where bleaching of the dye is only of the order of 10–20%, the absorption at λ_l is 1.2% when our dye laser has reached one-half of its initial output. It is consequently possible to estimate τ values of new dyes by the use ofA terms through the relationshipA ₁τ₁=A ₂τ₂ where τ₁ of Dye 1 has been calibrated in the same dye laser system.