Photo-orientation by multiphoton photoselection

We present evidence of photoselection by polarized multiphoton absorption (MPA) in an azo dye, i.e., Disperse Red 1 (DR1), dispersed in films of poly(methyl-methacrylate). MPA of DR1 at a fundamental of 785 rim, from a pulsed, regeneratively amplified, Ti:sapphire laser, results in photobleaching of the dye, and linearly polarized MPA of DR1 creates anisotropy, a feature that is indicative of orientational hole burning by MPA. The slopes of the early-time evolution of the isotropic absorbance and anisotropy show a dependence on the 3.65 +/- 0.15 power of the excitation laser intensity, and the dynamics of MPA-induced orientation are described by a theoretical model for MPA selective bleaching. (c) 2006 Optical Society of America.