Controlling Polymer Microstructure Through the Coherence of Light

Abstract

<p>This thesis describes modulation instability of a broad beam of partially spatially incoherent laser light propagating in a photopolymerisable organosiloxane. Refractive index changes due to photoinitiated free-radical polymerisation lead to a nonlinear regime in which even weak perturbations in the optical field become amplified. These trigger the spontaneous division of the beam into multiple self-trapped filaments of light. By tuning the spatial coherence of the beam, it was possible to vary the diameter of the self-trapped filaments. Quantitative analyses showed that the relation between filament diameter and spatial incoherence was consistent with a previously developed theoretical model. Because refractive index changes in the photopolymer are irreversible, modulation instability led to a permanent array of self-induced waveguides. In this way, it was possible to control the dimensions of the spontaneously formed polymer microstructure by tuning the incoherence of the optical field.</p>