| CPC G01B 9/02057 (2013.01) [G01B 11/2441 (2013.01); G01B 2290/70 (2013.01)] | 1 Claim |
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1. A method for improving a contrast of an interferogram in a Fizeau interferometer, wherein the Fizeau interferometer comprising a light source for emitting a light beam that travels along a light path, wherein
a first part of the light path extends between the light source and a reflective test surface positioned on a support of the Fizeau interferometer, wherein
a reference surface is arranged in the first part of the light path between the light source and the support for the test surface, wherein
a second part of the light path extends from the test surface to the reference surface and then to an imaging system of the Fizeau interferometer for measuring light incident from the second part of the light path, wherein
the imaging system is configured for measuring an interferogram generated by interfering a reference light beam and a test light beam, wherein the reference surface is a polarizing partially reflective reference surface, so that the reference light beam is formed by the reference surface through partial reflection and polarization of the light beam emitted by the light source and incident along the first part of the light path, which the reference light beam is reflected by the reference surface towards the imaging system along the second part of the light path, wherein
the reference light beam has a first polarization angle, the test light beam is formed by passing of the light beam, which is incident along the first part of the light path, through the reference surface along the first part of the light path towards the test surface, which the test light beam is polarized by the reference surface and which the test light beam is reflected by the test surface towards the reference surface and then to the imaging system along the second part of the light path, wherein
the test light beam has a second polarization angle, wherein the first polarization angle and the second polarization angle are different, and wherein the Fizeau interferometer further comprises a first polarizer which is placed between the reference surface and the imaging system in the second part of the light path, wherein
the first polarizer is configured to allow light of a third polarization angle to pass towards the imaging system, the first polarizer is a first variable angle polarizer such that the third polarization angle is a variable third polarization angle, and the first polarizer provides control over a beam ratio of the reference light beam and the test light beam at the imaging system to improve a contrast of the interferogram, and
wherein the method comprises:
illuminating the reference surface and the test surface with the light source;
determining the contrast of the interferogram measured by the imaging system;
varying the third polarization angle to vary the contrast of the interferogram; and
improving the contrast of the interferogram by varying the third polarization angle.
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