Light-induced spiral mass transport in azo-polymer films under vortex-beam illumination

TL;DR

This paper reports the discovery of spiral relief patterns on azobenzene polymer films induced by focused Laguerre-Gauss beams, revealing new insights into light-induced mass transport mechanisms influenced by optical vortex properties.

Contribution

The study introduces a novel observation of spiral reliefs formed by vortex-beam illumination and proposes a surface interference model explaining this phenomenon.

Findings

Spiral relief patterns depend on vortex topological charge.

Reliefs are sensitive to wavefront handedness.

The model explains the interference of optical field components.

Abstract

When an azobenzene-containing polymer film is exposed to a non-uniform illumination, a light-induced mass migration process may be induced, leading to the formation of relief patterns on the polymer free surface. Despite a research effort of many years and several proposed models many aspects of this phenomenon remain not well understood. Here we report the appearance of spiral-shaped relief patterns on the polymer under the illumination of focused Laguerre-Gauss beams, having helical wavefront and an optical vortex at their axis. The induced spiral reliefs are sensitive to the vortex topological charge and to the wavefront handedness. These findings are unexpected, because the "doughnut"-shaped intensity profile of Laguerre- Gauss beams contains no information about the wavefront handedness. We propose a model that explains the main features of this phenomenon from the surface-mediated interference of the longitudinal and the transverse components of the optical field. These results may find applications in optical micro- and nanolithography and optical-field.