Holographic studies of azobenzene-containing low-molecular-weight organic glasses

Abstract

The formation of phase and surface relief gratings in low-molecular-weight organic glasses containing azobenzene moieties has been studied with holographic methods. Advantages of this class of materials are the simple synthesis, the perfectly amorphous phase, and the possibility of blending them with polymers. Surface relief gratings are formed very efficiently in molecular glasses, and this process can be explained by the gradient force model. Heights up to 610 nm were measured; the temporal evolution of the diffraction efficiency could be reproduced in computer simulations. For technical applications, the surface relief gratings can easily be duplicated by replica molding. Since surface gratings are detrimental to holographic data storage at high densities, it is also possible to suppress their formation by using proper polarizations of the writing beams. Reorientation of the azobenzene groups in the bulk of the glasses and angular multiplexing was demonstrated and the thermal stability of the corresponding phase gratings was studied. Different combinations of molecular cores and substituents at the azobenzene moieties were investigated to find the best systems which yield a high sensitivity and fast grating build-up.