WAVELENGTH DEPENDENCE OF THE NONLINEAR ABSORPTION PROPERTIES OF LASER-DYES IN SOLID AND LIQUID SOLUTIONS

Nonlinear transmission properties of laser dyes rhodamine 6G in solid and liquid solution and pyrromethene 557 and 556 in liquid solution in the ultraviolet and visible spectral regions have been studied using nanosecond laser pulses. The dyes behave as saturable absorbers when i rradiated a 534 nm, but their transmittance exhibits no intensity depe ndent behavior or decreases with increasing laser intensity at 337 and 308 nm irradiation wavelengths. A five-level theoretical model incorp orating excited-state absorption and stimulated emission was used to c ompute the dependence of transmittance with intensity in the studied s olutions and to estimate the absorption cross sections of the first ex cited single state of the dye molecules. The different nonlinear behav ior of the studied dyes depending on the irradiation wavelength can be understood in terms of the relative values of the absorption cross se ctions of the ground and first excited singlet state at the irradiatio n wavelength. (C) 1998 Elsevier Science B.V. All rights reserved.