Polarization interferometer

A polarization interferometer for determining a surface roughness of a test object, comprising:

• an illumination source that produces light having multiple wavelengths;
• polarization interferometer optics that split the light into two orthogonally polarized beams comprising a reference beam and a test beam, wherein the test beam is incident on and is returned from the test object, the polarization interferometer optics recombine the test beam and the reference beam into a combined beam;
• at least one spectral filter that spectrally filters the combined beam into two spectral channels, a first spectral channel having a first center wavelength and a second spectral channel having a second center wavelength, wherein the first center wavelength and the second center wavelength are different;
• two pixelated polarization phase sensors configured to capture images of the two spectral channels at a same time, wherein the two pixelated polarization phase sensors are configured to produce a phase map of a surface of the test object corresponding to an equivalent wavelength for the first center wavelength and the second center wavelength;
• and
• a computer configured to determine the surface roughness of the test object based on the phase map, wherein the surface roughness of neighboring height variations are greater than 20 nanometers (nm) root mean square (RMS).