  We report the realization of an optical filter based on an optical vortex
mask designed to exclusively detect a weak coherent laser field in the presence
of much stronger spatially-overlapping field. We demonstrate the performance of
such an optical vortex filter to eliminate the strong control field and detect
only a weak optical field's transmission under the conditions of
electromagnetically induced transparency. The attractive feature of such filter
is its insensitivity to optical field frequencies and polarizations, which
makes it applicable for a wide range of coherent processes.
