Laser Induced Self-Action Phenomena in a Photopolymerisable Medium

Abstract

<p>The nonlinear propagation of a visible, continuous wave laser beam in a photopolymerizable organosiloxane was studied at intensities ranging across 10 orders of magnitude (3.2x10-5 to 12732 W /cm2). The process was characterised in detail through spatial intensity profiles of the beam, temporal monitoring of its width and peak intensity combined with optical microscopy of the resulting self-induced structures.</p> <p>These observations revealed a rich diversity of dynamic phenomena during nonlinear light propagation in different intensity regimes including (i) optical self-trapping (ii) in situ sequential excitation of high-order modes (corresponding to optical fiber modes) in self-written cylindrical waveguides, (iii) variations in modal composition during the transition of self-written waveguides from single to multimode guidance, (iv) generation of spatial diffraction rings that propagated over long distances (>Rayleigh length), (v) transformation of the Gaussian beam into an unstable single ring, which collapsed into azimuthally symmetric filaments and (vi) complete beam filamentation.</p> <p>Extensive and quantitative analyses of spatial beam profiles provided insight into the mechanisms underlying each of these phenomena, particularly the significance of the spatial profile (gradient) of refractive index changes induced in the medium. The experimental findings were consistent with results of numerical simulations of nonlinear light propagation in the corresponding intensity range that were implemented through the beam propagation method with the software BeamPROP™. The results of these comprehensive series of experimental and theoretical studies provide a deep understanding of the dynamics of nonlinear light propagation in a photopolymerizable medium and are consistent with some predictions of earlier theoretical models.</p>