Excitation used to produce luminescence is cancelled using interference with an excitation cancelling beam by controlling or setting a phase difference. An excitation beam and an excitation cancelling beam are produced from a common source and the excitation beam directed quantum light emitter to produce luminescence. A residual excitation beam and the excitation cancelling beam are coupled to interfere destructively so that the luminescence is available for detection or otherwise without substantial portions of the excitation beam.