Fast surface profilometry utilizing structured illumination microscopy based on the time-domain phase-shift technique.

Abstract

Structured illumination microscopy (SIM) has attracted much research interest due to its high accuracy, strong adaptability, and high efficiency. Existing SIM is mainly based on the phase-shift technique, Hilbert transform technique, and global Fourier transform technique. The phase-shift technique is most widely applied for its higher accuracy, and both the phase-shift technique and Hilbert transform technique suffer from lower speed because multiple images are needed to obtain modulation information for each scanning step. The global Fourier transform technique has a higher speed, but the high-frequency information of the sample will inevitably be lost because a filter window is used. As a result, the global Fourier transform technique is limited to smooth surfaces. In this paper, a fast surface profilometry using SIM is proposed. It is based on the time-domain phase-shift technique (SIM-TPT), which combines one-fringe projection and phase shift. In this proposed measurement system, vertical scanning of the object is synchronized with the switching of the phase-shifted fringe pattern. As a result, only one fringe pattern must be projected, which enables a point-to-point processing defined as the local Fourier transform method in this paper to be utilized to extract the modulation information that will preserve the high-frequency information of the image so it can be applied to both smooth and rough surfaces. Compared to conventional SIM, SIM-TPT has a higher speed because it is a simpler system and can be applied to complex structures such as high roughness surfaces and steep edges.