LUO Yong, LI Tuo, LI Gui-lin, SHI Yi-shi*

(1.School of Optoelectronics,University of Chinese Academy of Sciences,Beijing 100049,China； 2.Academy of Opto-Electronics,Chinese Academy of Sciences,Beijing 100094,China； 3.School of Science,Xijing University,Xi′an 710123,China)

Abstract: In a traditional single beam multiple-intensity reconstruction(SBMIR) system, error is accumulated by multiple translational image sensors, which reduces the imaging effect and the effective resolution of the photoelectric imaging system. In this paper, a three-step coherent diffraction imaging system based on parallel plates is proposed. Three different diffraction planes are obtained by inserting or extracting two parallel plates and imaging and restoration reconstruction of complex amplitude objects are achieved. The numerical simulation and experiments show that the system overcomes the error accumulation problem of several translations in the SBMIR system, and one only needs to record three diffraction surfaces to avoid oversampling. The proposed optical system is easy to implement and has high repeatability.

Key words: the single-beam multiple-intensity;coherent diffraction imaging;parallel plates;complex amplitude

1 Introduction

引 言

Coherent Diffraction Imaging(CDI) is a lensless diffraction imaging technique[1-3]that has been rapidly developing with applications in adaptive X-ray imaging and related fields[4-8]. The CDI methods implemented in nowadays involve holography[9-10], wavefront detection reconstruction[11]and Gerchberg-Saxton′s(GS) algorithm for multiple diffraction information surfaces[12-13]. In general, single-step diffraction imaging is not suitable for complex amplitude recovery reconstruction because only one diffraction pattern is recorded. Therefore, an improved GS algorithm was produced[14-15], along with random binary pure phase modulation[16], rotational phase modulation[17], single-beam multi-intensity wavefront reconstruction(SBMIR) and other technical solutions[18-21]. However, among the many schemes, most of them are limited to the use of computers for numerical simulation. Also, specific optical imaging experiments for the schemes have not been implemented and they have no proposed specific experimental procedure. For this reason, further verification is needed to give plausibility to the methods and reproducibility of their experiments. Traditional SBMIR technology has been studied using numerical simulation analysis and specific experimentation. The phase recovery problem has also been solved. SBMIR methodology generally involves fixing a CCD camera on a precision stage and adopts a mechanical stepping mode. This easily causes the experimental image to have problems that result from shaking equipment, thereby reducing image resolution and quality. Furthermore, this technique usually requires that 10-20 diffractive faces be collected and recorded, which introduces the issue of oversampling defects. The above problems lead to difficulty repeating experiments and cause the technology to be less useful in real-world applications.

相干衍射成像(Coherent Diffraction Imaging，CDI)，是一种无透镜衍射成像技术[1-3]，从提出至今快速发展并应用于自适应成像、X射线成像等相关领域[4-8]。CDI的实现方法有基于全息术[9-10]、波前检测重建[11]和多个衍射信息面的Gerchberg-Saxton(GS)算法等[12-13]。通常，单步衍射成像因为只记录一幅衍射图像，无法适用于复振幅的恢复重建，所以基于此类相位恢复重建的问题，通常采用改进型的GS算法[14-15]、随机二元纯相位调制[16]、旋转相位调制[17]、单光束多强度波前重建(SBMIR)等技术方案[18-21]。然而，大部分方法都只局限于利用计算机进行数值模拟，具体的光学成像实验并未实现，也没有提出具体的实验方案。所以方法的实用性及实验的可重复性需要进一步验证。传统的SBMIR技术对数值模拟分析和具体实验都进行了研究，相位恢复问题得到了解决。但是，传统的SBMIR技术大多是将图像传感器CCD固定于精密平移台上，采用机械移动的步进方式，导致实验图像有抖动问题。从而降低了成像分辨率和质量，而且此技术通常需采集记录10～20个衍射面，有过采样的缺陷，上述问题及缺陷导致实验重复性较差，不利于技术方案的实际应用。

In order to solve and avoid the above issues, a three-step coherent diffraction imaging system based on parallel plates is proposed. The position of the CCD camera and the sample is fixed and two parallel plates are inserted in or extracted from the system. By doing so, three intensity information diffraction planes are quickly obtained and the sample pattern is eventually reconstructed by the recovery algorithm. The results of computer numerical simulation and actual optical experiments show that the system effectively avoids and solves the problem with shaking and the oversampling defects that exist in the traditional technical solutions. The proposed method is simple, quick to perform and repeatable while also producing images that are of significantly higher quality

为了解决和避免上述问题及缺陷，本文提出一种基于平行平晶的三步相干衍射成像系统，图像传感器CDD和样品的位置固定不变，采用依次在系统中插入或抽出2块平行平晶的方法，快速获得3幅强度信息衍射图，通过恢复算法最终重建样品图像。计算机数值模拟和实际的光学实验结果表明：该系统有效解决了传统技术方案的抖动问题与过采样的缺陷，最重要的是系统的成像效果显著提升，且具有实验可重复性高，操作简单快捷的特点。……