Testing optical surfaces using two-frame phase-shifting interferometry

Abstract

Standard phase-shifting interferometry (PSI) generally requires collecting at least three phase-shifted interferograms to extract the physical quantity being measured. Here, we propose a simple two-frame PSI for the testing of a range of optical surfaces, including flats, spheres, and aspheres. The two-frame PSI extracts modulated phase from two randomly phase-shifted interferograms using a Gram-Schmidt algorithm, and can work in either null testing or non-null testing modes. Experimental results of a paraboloidal mirror suggest that the two-frame PSI can achieve comparable measurement precision with conventional multi-frame PSI, but has the advantages of faster data acquisition speed and less stringent hardware requirements. It effectively expands the flexibility of conventional PSI and holds great potential in many applications.