Tunable Optical High‐Order Differential Microscopy for Cell Structure Detection

Abstract Optical differential microscopy is an important tool for the detection and recognition of transparent biological objects. Among it, the first‐order optical differentiation is commonly utilized to aid in fast, label‐free, and contactless detection. However, the characterization of detailed contours for some smooth object areas may be limited, and a higher order operation needs to be executed. A tunable optical high‐order differential microscopy is proposed and implemented, in virtue of electric‐driven liquid crystal (LC). By electrically switching the working state of LC, the differential operation can be flexibly tuned in desired order, such as from zero‐order to first‐order and second‐order differentiations. Using this scheme, clear edge‐enhanced images of different‐contrast objects even transparent biological cells are experimentally acquired under multi‐wavelength cases. Specifically, based on the connection between high‐order differential results and edge features, further gained in‐depth information in the size of light spot and structure of plant cells. The beam waist radius of a laser is determined as 0.35 ± 0.002 mm, and the cell wall thickness is estimated about 3 to 5 microns. These results may open the avenue for biological imaging and microscopic measurement.