  We use a microwave cavity to investigate the influence of a movable absorbing
center on the wave function of an open quantum dot. Our study shows that the
absorber acts as a position-selective probe, which may be used to suppress
those wave function states that exhibit an enhancement of their probability
density near the region where the impurity is located. For an experimental
probe of this wave function selection, we develop a technique that we refer to
as scanning Fourier spectroscopy, which allows us to identify, and map out, the
structure of the classical trajectories that are important for transmission
through the cavity.
