Detailed studies of the dynamics of a continuous wave, visible laser beam propagating in a photopolymerizable
organosiloxane are presented. Experiments carried out at intensities ranging across ten orders of magnitude (3.2 x 10<sup>-5</sup>
Wcm<sup>-2</sup> to 12732 Wcm<sup>-2</sup>) revealed three types of nonlinear behaviour. In the low-intensity regime, the beam
self-trapped and exhibited complex oscillatory behaviour, which signified the excitation of high-order modes in its
self-inscribed waveguide during self-trapping. This is consistent with previous theoretical predictions of self-trapping
in 1-photon systems including photopolymers. In the mid-intensity regime, the beam underwent spatial self-phase
modulation, which elicited spatial diffraction rings. While this phenomenon has been observed in Kerr, liquid crystals
and absorptive materials, it has until now been neither theoretically nor experimentally observed in photopolymers.
Rapid and large refractive index changes induced in the high-intensity regime caused filamentation of the beam. These
studies provide a comprehensive overview of nonlinear light propagation in photopolymers.