  The Path-Length Spectra of mesoscopic systems including diffractive
scatterers and connected to superconductor is studied theoretically. We show
that the spectra differs fundamentally from that of normal systems due to the
presence of Andreev reflection. It is shown that negative path-lengths should
arise in the spectra as opposed to normal system. To highlight this effect we
carried out both quantum mechanical and semiclassical calculations for the
simplest possible diffractive scatterer. The most pronounced peaks in the
Path-Length Spectra of the reflection amplitude are identified by the routes
that the electron and/or hole travels.
