Pixelated Phase-Mask Dynamic Interferometer

We demonstrate a new type of spatial phase-shifting, dynamic interferometer that can acquire phase-shifted interferograms in a single camera frame. The interferometer is constructed with a pixelated phase-mask aligned to a detector array. The phase-mask encodes a high-frequency spatial interference pattern on two collinear and orthogonally polarized reference and test beams. The phase-difference between the two beams can be calculated using conventional N-bucket algorithms or by spatial convolution. The wide spectral response of the mask and true common-path design permits operation with a wide variety of interferometer front ends, and with virtually any light source including white-light.

Phase-stepping interferometry is an established method for measuring a variety of physical parameters ranging from the surface figure of mirrors to the displacement of solid objects.1 Phase-shift interferometers typically have an element in the path of the reference wavefront that introduces three or more known phase steps or shifts. By detecting the intensity pattern with a detector at each of the phase shifts, the phase distribution of the object wavefront can be quantitatively calculated independent of any attenuation in either of the reference or object wavefronts. Both continuous phase gradients and discontinuous phase gradients (speckle waves) can be measured using this technique.