Nanometer resolution of 2D single-shot low-coherence & comb-based profilometry based on the effect of discrete height of spatial phase modulator surface

A 2D single-shot comb-based interferometer is well known as a powerful tool for inline inspection owing to its high speed, extensive measurement range, and anti-vibration. However, nanometer resolution is still a milestone that has not been achieved in comb-based interferometers owing to the precision limitation caused by the discrete profile of the spatial phase modulator (SPM) device, typically in the range of several micrometers. Therefore, this study confirms 2D single-shot comb-based profilometry at sub-micron and nanometer-scale resolutions. The system first investigates the effect of the discrete limitation of the SPM surface profile and then verifies the submicron detection ability of the optical frequency comb-based setup. It was quantitatively shown that the highest resolution can be obtained by properly setting the step size of the spatial phase modulator and the SPM surface resolution of the imaging optics. The highest profilometry resolution was recorded at 26.4 nm in a short measurement range, while the setup using the optical comb source with millimeters measurement range for industrial application also can achieve a resolution of approximately 259.2 nm. The results demonstrate the system feasibility in overcoming the discrete limitations of the SPM profile. It also demonstrates for the first time that the so-called 2D single-shot comb-based interferometer can achieve nanometer-scale profilometry resolution covering the measurement range from tens of millimeters to sub-micrometer detection.