  We demonstrate a novel method to measure the Nth-order (N=1, 2, 3, 4)
interferometric autocorrelation with high sensitivity and temporal resolution.
It is based on the combination of linear absorption and nonlinear detection in
a superconducting nanodetector, providing much higher efficiency than methods
based on all-optical nonlinearities. Its temporal resolution is only limited by
the quasi-particle energy relaxation time, which is directly measured to be in
the 20 ps range for the NbN films used in this work. We present a general model
of interferometric autocorrelation with these nonlinear detectors and discuss
the comparison with other approaches and possible improvements.
