  It is shown that coherent scatterings by an ordered vortex lattice are
critically enhanced for quasi particles moving in cyclotron orbits on the Fermi
surface through vortex core regions, thus generating significant quasi-periodic
oscillating contributions to the SC free energy as a function of the inverse
magnetic field. The mean frequency of the oscillation provides a fingerprint of
the vortex lattice geometry. Vortex-lattice disorder, tends to suppress this
oscillatory component.
