| dc.description.abstract | In this thesis, a novel optics-based autofocusing microscope was developed based on triangulation, knife-edge method, centroid method, astigmatic method and two optical paths. According to the different distance between the sample and the objective lens, the shape of the laser spot also varies and can be detected by a CCD sensor, i.e., the defocus distances can be found.
In this structure of the proposed autofocusing microscope, the light beam is expanded and collimated by means of an expander lens and is then bisected by a knife. The light beam is then passed through BS1, mirror, objective lens and is incident on the sample surface. The laser light reflected from the sample surface passes back through the objective lens, mirror, BS1 and is then incident on a BS2, where it is split into two separate optical paths(Optical Path I and II). Finally, the two separate optical paths are passed through two cylindrical lens, where they are perpendicular to one another and is then incident on CCD1 and CCD2, respectively. The Optical Path I can be used to implement an auto-focus with both a large range of auto-focus distances and low focus accuracy. The Optical Path II can be used to implement an
auto-focus with both a short range of auto-focus distances and high focus accuracy. The two optical paths are combined using a self-written autofocus-processing algorithm to realize an autofocusing microscope.
The simulation and experimental results show that compared to conventional optics-based autofocusing microscopes with biconvex lens, the proposed microscope system has a higher focusing accuracy. In addition, under the same focusing accuracy, the focusing times of the proposed microscope system using two optical paths are less than that of the proposed microscope system using a single optical path. | en_US |