Interferometry systems and methods

An apparatus comprising:

• an interferometer comprising a main cavity and an auxiliary reference surface, the main cavity comprising a partially reflective surface defining a primary reference surface and a test surface,
• the interferometer being configured to direct input electromagnetic radiation to reflect from the auxiliary reference surface, to reflect from the primary reference surface and to reflect from the test surface,
• the interferometer being further configured to direct the electromagnetic radiation reflected from the test surface, the primary reference surface, and the auxiliary reference surface to a multi-element detector to interfere with one another to form an interference pattern,
• wherein the auxiliary reference surface is configured to introduce spatial carrier fringes in the interference pattern at the multi-element detector.

A system comprising:

• a multi-element detector;
• a Fizeau interferometer comprising a primary reference surface and a test surface, the interferometer being configured to interfere electromagnetic radiation reflected from the primary reference surface and electromagnetic radiation reflected from the test surface to form an interference pattern at the multi-element detector;
• a means for generating spatial carrier fringes in the interference pattern at the multi-element detector;
• and
• an electronic controller configured to determine information about the test surface based on the interference pattern and the spatial carrier fringes.