Refractive scanning interferometer

A scanning interferometric system comprising:

• an aperture that receives an incident light beam at a receiving angle;
• a beam splitter configured to split the incident light beam into a first beam and a second beam;
• a first and a second reflector arranged to reflect the first beam and second beam, respectively, towards a combining optical element;
• and
• a refractive Optical Path Difference (rOPD) assembly interposed between the beam splitter and the first reflector;
• wherein the rOPD Assembly comprises a pivotable refractor able to pivot about an axis extending substantially perpendicular to a direction of travel of the first beam in order to induce and alter a difference in path length between the first beam and the second beam, thereby phase-shifting the first beam relative to the second beam;
• and
• the combining optical element is configured to emit an output beam having an interference pattern induced by the phase-shifted first beam and the second beam interfering with one another;
• further wherein the interference pattern contains a phase discrepancy with a magnitude dependent upon the receiving angle of the incident light beam, the phase discrepancy being induced during refraction of the first light beam;
• the aperture has a critical receiving angle, such that incident light having a receiving angle greater than the critical receiving angle subsequently results in the phase discrepancy in the interference pattern of the output beam having magnitude sufficient to render a produced interference pattern illegible, invisible or otherwise undetectable;
• and
• the rOPD Assembly refracts the first light beam an even number of times with the phase discrepancy being a vector sum of a first phase discrepancy induced by a first refraction and a second phase discrepancy induced by a second refraction;
• the rOPD Assembly being configured such that the first phase discrepancy is substantially opposite in direction to the second phase discrepancy, a portion of the first and second phase discrepancies cancelling one another out to decrease magnitude of the phase discrepancy.