  We report on interferometric autocorrelation measurements of broadband
supercontinuum light in the anomalous dispersion regime using two-photon
absorption in a GaP photodetector. The method is simple, low-cost, and provides
a direct measure of the second-order coherence properties, including
quantitative information on the coherence time and average duration of the
supercontinuum pulses as well as on the presence of temporally coherent
sub-structures. We report measurements in regimes where the supercontinuum is
coherent and incoherent. In the former case, the interferometric measurements
are similar to what is observed for mode-locked laser pulses while in the
latter case the interferometric measurements and coherence properties are shown
to have characteristics similar to that of a stationary chaotic light source.
