  The interaction of light beams with resonant structures has led to the
development of various optical platforms for sensing, particle manipulation,
and strong light-matter interaction. In the current study, we investigate the
manifestations of the bound states in continuum (BIC) on the in plane and out
of plane shifts (referred to as Goos-Hanchen (GH) and Imbert-Fedorov (IF)
shifts, respectively) of a finite beam with specific polarization incident at
an arbitrary angle. Based on the angular spectrum decomposition, we develop a
generic formalism for understanding the interaction of the finite beam with an
arbitrary stratified medium with isotropic and homogeneous components. it is
applied to the case of a Gaussian beam with p and circularly polarized light
incident on a symmetric structure containing two polar dielectric layers
separated by a spacer layer. For p-polarized plane wave incidence one of the
coupled Berreman modes of the structure was recently shown to evolve to the
bound state with infinite localization and diverging quality factor coexisting
with the other mode with large radiation leakage (Remesh et al. Optics
Communications, 498:127223, 2021). A small deviation from the ideal BIC
resonance still offers resonances with very high quality factors and these are
exploited in this study to report giant GH shifts. A notable enhancement in the
IF shift for circularly polarized light is also shown. Moreover, the reflected
beam is shown to undergo distortion leading to a satellite spot. The origin of
such a splitting of the reflected beam is traced to a destructive interference
due to the left and right halves of the corresponding spectra.
