  We report on the active stabilization of a Michelson interferometer at an
arbitrary phase angle with a precision better than one degree at $\lambda =
632.8$ nm, which corresponds to an optical path difference between the two arms
of less than 1 nm. The stabilization method is ditherless and the error signal
is computed from the spatial shift of the interference pattern of a reference
laser, measured in real-time with a CCD array detector. We discuss the
usefulness of this method for nanopositioning, optical interferometry and
quantum optical experiments.

Optics