Abstract: An apparatus for detecting volumetric leaks includes an arrangement for measuring linear displacement of a surface, including the surface of a liquid. The arrangement includes a beam generator for directing a collimated or coherent beam of energy onto a surface, a non-planar mirror to receive the beam as it reflects from the surface, and a receptor for receiving the beam as it is reflected from the mirror. Changes in position of a footprint of the beam on the receptor correlate to changes in displacement of the surface and accordingly, volumetric changes of a contained liquid. The non-planar mirror amplifies or exaggerates the changes in the position of the footprint relative to linear displacement of the surface so as to enable detection of small displacements of the surface.