Design and characterization of high-performance autofocusing microscope with zoom in/out functions

Autofocusing is a critical function in on-line or off-line automated vision inspection in the manufacturing fields. Accordingly, design of high-performance autofocusing microscopes is an important issue. The present group recently developed a novel laser-based autofocusing microscope comprising two optical paths, which provided a large linear autofocusing range and a rapid response with no reduction in the focusing accuracy (Liu et al. in Appl Phys B 109:259–268, 2012). In the present study, the focusing response of the developed autofocusing microscope is further improved by replacing the two optical paths with one tunable optical zoom system. The proposed autofocusing microscope is characterized numerically by means of commercial software ZEMAX simulations and is then verified experimentally using a laboratory-built prototype. The simulation and experimental results show that compared to the developed autofocusing microscope with two optical paths, the proposed autofocusing microscope achieves a rapid focusing response (less than 3.5 s) under the same autofocusing range (±1500 μm) and focusing accuracy (focusing accuracy of ≤1 μm, repeatability of ±1 μm). Consequently, it confirms the proposed autofocusing microscope has potential for automated vision inspection and optical applications.