  The 2nd and 3rd order nonlinear microwave response of a superconducting
YBa2Cu3O7 thin film resonator was synchronously measured using three input
tones. This technique permits the local measurement, and hence mapping, of
intermodulation distortion (IMD) inside the resonator. 2nd and 3rd order IMD
measured with a fixed probe relaxed in remarkably different ways after the
removal of a static magnetic field. The 2nd order IMD relaxed by two different
magnetic processes, a fast process that appears related to bulk remanent
magnetization, and a slow process that fits the description of Bean and
Livingston. The 3rd order IMD relaxes by only one process which is distinct
from the two processes controlling 2nd order relaxation.
