We report the two-photon induced photoisomerization of 3-[1-(1,2- dimethyl-1H-indol-3-yl)-ethylidene]-4-isopropylidene-dihydro-furan- 2,5-dione (1), a photochromic compound with (lambda) maxequals385nm, using 775 fs pulses. The resulting photoisomer has a (lambda) maxequals582 nm. The kinectic rate contant for the isomerization reaction w as measured at two different intensities (two different powers), showing a quadratic dependence with respect to the pump intensity. Results of pump-probe solution phase experiments and guest/host polymer thin film interferometric imaging studies are shown. A two-photon absorption molecular cross-section (sigma) 2equals10.3 x 10- 45 cm4 s/photon was measured using Z-scan, supporting a two photon induced isomerization process.
Zscan technique is a powerful method to determine the sign and magnitude of the nonlinear refractive index of optical materials [1]. In this technique the sample is illuminated by a focused Gaussian beam. An aperture is placed between the sample and the detector, and the light transmitted through the aperture is monitored as the sample is moved along the propagation path of the beam through the focal region. The transmittance of another probe beam that is distorted with the refractive index changes caused by the illuminating beam, may be measured as well in the so called two-color extension of this technique [2,3]
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