  In this work we study the walk-off of the beam from the interrogation spot
during rotation in surface plasmon resonance experiments using prism-based
coupling such as the widespread Kretschmann configuration. The impossibility of
maintaining a stationary footprint on the sensing surface with a fixed rotation
axis can be of high importance. This would be specially so if samples are not
homogeneous such as in arrays for multiplexing. By theoretically analyzing the
behavior of the walk-off during rotation around an arbitrary fixed axis, we
find an optimal and simple configuration to minimize this effect. The proposed
setup is experimentally tested to verify the results and to show its ease of
implementation. Interestingly, the conclusions reached may also be applied to
other techniques employing reflection prisms.
