Near-field modulation ptychography

Ptychography a quantitative phase imaging technique that can simultaneously achieve high spatial resolution and large field of view. Due to the simplicity in system structure and stability in convergency, it has been applied to a variety of scenarios. However, Ptychography is limited by its data acquisition method, which cannot convert the slowly changing phase into intensity changes for detection. Moreover, in experiments, it is usually necessary to recover samples and probe at each scanning position, thus the problem of "blind ptychography" exists. In addition, high-quality ptychography reconstruction relies on accurate tracking of the scanning position, but high-precision scanning equipment is expensive and difficult to be applied in many engineering fields. In view of the above, this paper proposes a modulation ptychography (MP) solution by adding a diffuser to the ptychography system, which converts the phase retardation into the intensity information. And the diffuser, which is preset in the system, can be used as a fixed component in the system after calibration, so as to solve the problem of blind ptychography. This paper also proposes a gradient correlation position tracking algorithm, which has a sub-pixel accuracy of position tracking for the scanning with overlap rate of 85% and above, which reduces the demand of high-precision positioning system. Simulations and optical experiments carried out to demonstrate the effectiveness of the method. This work will open the way for the application of Ptychography in both fundamental and applied sciences.