A test cell for determining expansion or contraction of a sample contained therein includes, a test cell body, a reflective surface within the test cell body, the reflective surface moveable responsive to expansion or contraction of the sample, a displacement sensor system exterior of the cell body, the displacement sensor system having a transmitter for transmitting directed electromagnetic radiation and a sensor for sensing electromagnetic radiation, a lens provided in the cell body, the lens constructed to allow electromagnetic radiation to pass therethrough. The transmitter, reflective surface, and sensor are constructed and positioned such that directed electromagnetic radiation transmitted from transmitter toward reflective surface is reflected from reflective surface toward the sensor. In an exemplary embodiment, the lens is provided in a cell upper plug, with the translating member positioned for linear displacement toward and away from the lens responsive to expansion and contraction of a material sample.