Abstract
To reduce the long data acquisition time of the common mechanical scanning based Ptychographic Iterative Engine (PIE) technique, the digital micro-mirror device (DMD) is used to form the fast scanning illumination on the sample. Since the transverse mechanical scanning in the common PIE is replaced by the on/off switching of the micro-mirrors, the data acquisition time can be reduced from more than 15 minutes to less than 20 seconds for recording 12 × 10 diffraction patterns to cover the same field of 147.08 mm2. Furthermore, since the precision of DMD fabricated with the optical lithography is always higher than 10 nm (1 μm for the mechanical translation stage), the time consuming position-error-correction procedure is not required in the iterative reconstruction. These two improvements fundamentally speed up both the data acquisition and the reconstruction procedures in PIE, and relax its requirements on the stability of the imaging system, therefore remarkably improve its applicability for many practices. It is demonstrated experimentally with both USAF resolution target and biological sample that, the spatial resolution of 5.52 μm and the field of view of 147.08 mm2 can be reached with the DMD based PIE method. In a word, by using the DMD to replace the translation stage, we can effectively overcome the main shortcomings of common PIE related to the mechanical scanning, while keeping its advantages on both the high resolution and large field of view.
Highlights
Compared to imaging techniques based on the intensity detection, phase imaging can obtain higher image contrast especially in imaging the semi-transparent biological samples, and since they can provide another perspective for the sample observation, phase imaging is becoming more and more important for medical examinations and disease diagnoses [1,2]
In comparison with traditional coherent diffraction imaging (CDI) techniques using Gerchberg-Saxton algorithm, Error Reduction algorithm and Hybrid Input Output algorithm, which suffer from shortcomings of small field of view, poor convergence speed and low reliability especially in imaging samples with complex structures, Ptychographic Iterative Engine (PIE) has obvious advantages of high convergence speed, high reliability, speckle free reconstructions and infinitely large field of view in theory, making PIE an outstanding phase imaging technique
To overcome these shortcomings of common PIE techniques, digital micro-mirror device (DMD) based PIE method is proposed to achieve the large field of view (FoV), fast speed data acquisition and high quality reconstruction simultaneously
Summary
Compared to imaging techniques based on the intensity detection, phase imaging can obtain higher image contrast especially in imaging the semi-transparent biological samples, and since they can provide another perspective for the sample observation, phase imaging is becoming more and more important for medical examinations and disease diagnoses [1,2]. Single-shot PIE methods [32,33] fitting for real time measurements often suffer from small FoV (less than 5 mm2), limiting their observation capability, the reconstruction quality especially the signal to noise ratio is still much lower than that of common PIE because of its low data redundancy To overcome these shortcomings of common PIE techniques, digital micro-mirror device (DMD) based PIE method is proposed to achieve the large field of view (FoV), fast speed data acquisition and high quality reconstruction simultaneously. DMD has been used in other imaging techniques including the tomographic phase microscopy and Fourier ptychographic microscopy to realize the phase measurement, where it was adopted mainly to avoid the rotating of the sample or to reduce the position-error of the light source by forming multidirectional illumination on the sample [34,35] Quite different from these two existing techniques, our proposed method uses the on/off switching of the micro-mirrors of DMD to replace the mechanical scanning of the sample in common PIE. The main shortcomings of common PIE were successfully overcome by using a DMD to replace the mechanical translation stage, achieving the large FoV, the high imaging quality and the high imaging speed simultaneously
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