Complex amplitude mapping based on adaptive autofocusing algorithm

Abstract

Since a complex amplitude distribution can be obtained in only a single two-dimensional plane using conventional imaging techniques, it is hard to obtain in-focus complex amplitude of three-dimensional structure (not a thin object) or multiple objects in different depth positions. The disadvantage often turns an obstacle to practical applications such as cell observation, particle measurement, and industrial inspection. To overcome the problem, adaptive autofocusing algorithm (AAA) is proposed. AAA consists of a complex amplitude measurement, numerical propagation, and local sharpness evaluation. In the proposed method, object positions can be determined for each pixel in the complex amplitude distribution using adaptively chosen area size of local sharpness evaluation. The proposed method gives a complex amplitude distribution which focuses on all objects or structure over an entire field of view. An optical experiment is carried out using the transport of intensity equation as a complex amplitude measurement. Performance of the proposed method is confirmed using living leaves of the moss Physcomitrella patens. Experimental results show that the object positions can be determined pixelwise and a focused complex amplitude distribution can be obtained by the proposed method.