Compact snapshot dual-mode interferometric system for on-machine measurement

•No reconfiguration (removing or adding the matching objective in the reference arm) is needed to switch the measurement modes.•The system is very compact in configuration with the dimension of 195 mm × 160 mm × 65 mm.•The stitching method is introduced for measuring large scale surface shape to address the major limitation of the compact configuration. To meet the need of on-machine metrology in optical manufacturing, a compact and snapshot dual-mode interferometric system is proposed for surface shape and roughness measurement. To simplify the measurement process between surface shape and roughness, a novel concept of using optical filters to separate the beam paths in the reference arm is introduced. A pixelated camera with a micro-polarizer array acquires four pi/2 phase-shifted interferograms simultaneously to minimize the environmental disturbance. Besides, the configuration-optimization-based subaperture stitching technique is introduced to extend the measurable aperture range. Both numerical analysis and experiments have been carried out to demonstrate the feasibility of the proposed compact snapshot dual-mode interferometer. The proposed system provides a powerful and portable tool to achieve on-machine surface characterization of various optical elements over a wide range of spatial frequencies and aperture sizes.