  We describe theoretically the process of multi-beam reflection in a
two-dimensional electron system with a lateral potential barrier. Due to
spin-orbital interaction, the reflection process leads to the formation of
three beams with different spin polarizations. The efficiency of spin
conversion can become small for smooth lateral barriers. Nevertheless, we
demonstrate that the spin-conversion effect remains strong for realistic
lithographical potentials and spin-orbit interactions in etched lateral
nano-structures. The system with a lateral barrier suggests useful applications
as a spin-filtering device. The expected quasi-classical adiabatic behavior
without spin conversion is found in the system with a very strong spin-orbit
interaction. We also consider the quasi-classical motion of electrons in a
system with boundaries in a magnetic field and two magnetic focusing
geometries.
