  Any slight variations in the fundamental constants of Nature, which may be
induced by dark matter or some yet-to-be-discovered cosmic field, would
characteristically alter the phase of a light beam inside an interferometer,
which can be measured extremely precisely. Laser and maser interferometry may
be applied to searches for the linear-in-time drift of the fundamental
constants, detection of topological defect dark matter through
transient-in-time effects and for a relic, coherently oscillating condensate,
which consists of scalar dark matter fields, through oscillating effects. Our
proposed experiments require either minor or no modifications of existing
apparatus, and offer extensive reach into important and unconstrained spaces of
physical parameters.
