Development of a new lateral shearing wavefront analyzer

Optical wavefront analyzers (WFS) play an important role in optical metrology. Previously, our team developed an optical wavefront analysis system called SPARROW ( shear phase analyzer, reflective/reflective optical wavefront), which utilized a right angle phase-shifting mechanism and a thermal resistance wire actuator to integrate opto-mechanical systems for wavefront measurements. The feature of the innovations was its compact size. During the measurement process, the whole SPARROW can be rotated by 90 degrees to obtain the wavefront gradients in two orthogonal directions which prevent it from being used for real-time measurements. To overcome this disadvantage, a beam rotation optical mechanism was proposed to replace the required step of the SPARROW rotation. The un-tested wavefront beam was polarized first and then split into two similar polarized beams. One of the beams along with its polarization was rotated by 90 degrees and the two orthogonal polarizations beams each carried information about the two wavefront directions. Then the rotated and unrotated beams were combined into one beam and it became incident into the phase-shifting mechanism to complete shear interferometry. Finally, the use of a PBS (polarizing beam splitter) separated the beams to achieve wavefront gradient measurements in two orthogonal directions. Therefore, we can reconstruct the wavefront with gradient data and undertake analysis. In addition, the improvement to the reconstruction process by the improvement of the thermal resistance wire actuator can reduce the time required for a single measurement cycle. With a combination of these efforts, a fast wavefront measurement can be obtained.