Intrinsic and photo-induced properties of high refractive index azobenzene based thin films [Invited

E Mavrona,V Apostolopoulos,M Kaczmarek,M Trapatseli,N Podoliak,J.-F Blach,G D’Alessandro,S Mailis,N Tabiryan

doi:10.1364/ome.8.000420

Abstract

We explore the limits of the photosensitive response of thin, 15 to 35 nm, films of complex azobenzene dyes. They show high refractive index, reaching 1.8, and significant photo-induced birefringence. We have successfully recorded strong, birefringent phase gratings with visible light and used the diffraction efficiency measurements to monitor their temporal evolution. The photo-induced gratings in such thin films were found not to be associated with any periodic surface relief, a typical feature in thicker azobenzene layers.

Highlights

Azobenzene based materials exhibit strong, selective photosensitivity and have been explored for different photonic applications [1]
The thickness of different PAAD layers and their uniformity depending on the speed of spincoating are presented in Tab. 1
The Jones matrices simplify considerably and we can consider the PAAD film as an isotropic grating with a refractive index modulation that depends on the polarization of the incident probe beam

Summary

Introduction

Azobenzene based materials exhibit strong, selective photosensitivity and have been explored for different photonic applications [1] They undergo photo-chemical isomerization from the trans form to the less stable cis form, under irradiation with UV and visible light [2] to achieve a photo-stationary composition that is wavelength and temperature dependent. The net effect of prolonged illumination of an azo-based layer is the preferential alignment of its molecules in the direction perpendicular to the incident light local polarization, which has been explored for writing gratings in guest-host liquid crystal systems [8]. This orientation process is reversible [9], but stable in ambient conditions. Such azobenzene layers can optically encode high resolution patterns, which are used as polarization gratings and spiral phase wave-plates [10,11,12]

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Conclusion