Research on depth of field expansion of three-dimensional measurement based on digital holographic microscopy

Phase measurement depth for traditional digital holographic Microscopy is limited by the depth of field of the Micro-objective. In order to expand the measurement range, an expanding depth of field of three-dimensional measurement method based on digital holographic microscopy technology is proposed. Firstly, two or more digital holograms can be captured by CMOS camera when the sample is located at different focusing positions. Then, every phase will be reconstructed by angle spectrum algorithm, because every reconstructed phase includes focused phase regions and defocused phase regions, the overlapped focused region between two adjacent reconstructed phases can be recognized by feature extraction. Lastly, the whole profile of sample can be calculated by using the iterative nearest point algorithm. The experiment of micro-array lens shows the proposed method is feasible.