  We observe and measure the nonequilibrium dynamics of optical vortices as a
function of propagation distance through a nonlinear medium. The precession of
a tilted-core vortex is quantified as is vortex-core sharpening, where the
infinite width of a linear core subsequently shrinks and approaches the healing
length of this nonlinear optical fluid. Experiments are performed with a
variable-length nonlinear medium: a nonlinear fluid in a tank with an output
window on a translating tube. This provides control over the distance the light
propagates in the fluid and allows for the measurement of the dynamics
throughout the entire propagation range. Results are compared to the
predictions of a computational simulator to find the equivalent dimensionless
nonlinear coefficient.
