Quantitative phase imaging (QPI) by differential phase contrast (DPC) with partially coherent illumination provides speckle-free imaging and lateral resolution beyond the coherent diffraction limit, demonstrating great potential in biomedical imaging applications. Generally, DPC employs weak object approximation to linearize the phase-to-intensity image formation, simplifying the solution to the phase retrieval as a two-dimensional deconvolution with the corresponding phase transfer function. Despite its widespread adoption, weak object approximation still lacks a precise and clear definition, suggesting that the accuracy of the QPI results, especially for samples with large phase values, is yet to be verified. In this paper, we analyze the weak object approximation condition quantitatively and explicitly give its strict definition that is applicable to arbitrary samples and illumination apertures. Furthermore, an iterative deconvolution QPI technique based on pseudo-weak object approximation is proposed to overcome the difficulty of applying DPC to large-phase samples without additional data acquisition. Experiments with standard microlens arrays and MCF-7 cells demonstrated that the proposed method can effectively extend DPC beyond weak object approximation to high-precision three-dimensional morphological characterization of large-phase technical and biological samples.

Bilayer graphene, which is highly promising for electronic and optoelectronic applications because of its strong coupling of the Dirac–Fermions, has been studied extensively for the emergent correlated phenomena with magic-angle manipulation. Due to the low energy linear type band gap dispersion relationship, graphene has drawn an amount of optoelectronic devices applications in the terahertz region. However, the strong interlayer interactions modulated electron-electron and electron-phonon coupling, and their dynamics in bilayer graphene have been rarely studied by terahertz spectroscopy. In this study, the interlayer interaction influence on the electron-electron and the electron-phonon coupling has been assigned with the interaction between the two graphene layers. In the ultrafast cooling process in bilayer graphene, the interlayer interaction could boost the electron-phonon coupling process and oppositely reduce the electron-electron coupling process, which led to the less efficient thermalization process. Furthermore, the electron-electron coupling process is shown to be related with the electron momentum scattering time, which increased vividly in bilayer graphene. Our work could provide new insights into the ultrafast dynamics in bilayer graphene, which is of crucial importance for designing multi-layer graphene-based optoelectronic devices.

Bayer阵列被广泛地应用于CMOS/CCD (complementary metal oxide semiconductor/charge-coupled device)等前端传感器中，用以对彩色图像进行压缩编码。通过解马赛克算法将Bayer阵列还原为红、绿、蓝彩色阵列，算法性能影响着成像有效分辨率和纹理细节。随着半导体工艺的发展和目标识别等新型应用需求的提出，图像设备向着高分辨率、低延迟的方向发展，原有的解马塞克算法遇到性能瓶颈。提出了一种基于FPGA (field programmable gate array)的实时解马赛克算法，能够准确地提取图像局部梯度方向并以引导实现色彩的插值复原，整体算法仅需7行数据延迟。算法设计充分考虑FPGA的硬件特点，设计了行缓存、梯度算子、梯度方向插值等模块，降低硬件开销。实验表明，本文算法在实现微米级延迟的同时，保持了对图像纹理细节区域的复原效果，在柯达数据集上的平均峰值信噪比达到38.26 dB。

计算光学显微成像技术将光学编码和计算解码相结合，通过光学操作和图像算法重建来恢复微观物体的多维信息，为显微成像技术突破传统成像能力提供了强大的助力。这项技术的发展得益于现代光学系统、图像传感器以及高性能数据处理设备的优化，同时也被先进的通信技术和设备的发展所赋能。智能手机平台作为高度集成化的电子设备，具有先进的图像传感器和高性能的处理器，可以采集光学系统的图像并运行图像处理算法，为计算光学显微成像技术的实现创造了全新的方式。进一步地，作为可移动通信终端，智能手机平台开放的操作系统和多样的无线网络接入方法，赋予了显微镜灵活智能化操控能力与丰富的显示和处理分析功能，可用于实现各种复杂环境下多样化的生物学检测应用。文中从四个方面综述了基于智能手机平台的计算光学显微成像技术，首先综述了智能手机平台作为光学成像器件的新型显微成像光路设计，接下来介绍了基于智能手机平台先进传感器的计算光学高通量显微成像技术，然后介绍了智能手机平台的数据处理能力和互联能力在计算显微成像中的应用，最后讨论了这项技术现存在的一些问题及解决方向。

In recent years, all-inorganic halide perovskite quantum dots (QDs) have drawn attention as promising candidates for photodetectors, light-emitting diodes, and lasing applications. However, the sensitivity and instability of perovskite to moisture and heat seriously restrict their practical application to optoelectronic devices. Recently, a facile ligand-engineering strategy to suppress aggregation by replacing traditional long ligands oleylamine (OAm) during the hot injection process has been reported. Here, we further explore its thermal stability and the evolution of photoluminescence quantum yield (PLQY) under ambient environment. The modified CsPbBr3 QDs film can maintain 33% of initial PL intensity, but only 17% is retained in the case of unmodified QDs after 10 h continuous heating. Further, the obtained QDs with higher initial PLQY (91.8%) can maintain PLQY to 39.9% after being continuously exposed in air for 100 days, while the PLQY of original QDs is reduced to 5.5%. Furthermore, after adhering CsPbBr3 QDs on the surface of a micro SiO2 sphere, we successfully achieve the highly-efficient upconversion random laser. In comparison with the unmodified CsPbBr3 QDs, the laser from the modified CsPbBr3 QDs presents a decreased threshold of 79.81μJ/cm2 and higher quality factor (Q) of 1312. This work may not only provide a facile strategy to synthesize CsPbBr3 QDs with excellent photochemical properties but also a bright prospect for high-performance random lasers.

All-inorganic perovskite has attracted significant attention due to its excellent nonlinear optical characteristics. Stable and low-toxic perovskite materials have great application prospects in optoelectronic devices. Here, we study the nonlinear optical properties of CsPbClxBr3-x (x=1, 1.5, 2) nanocrystals (NCs) glass by open-aperture Z-scan. It is found that the two- (2PA) and three-photon absorption (3PA) intensity can be adjusted by the treatment temperature and the ratio of halide anions. The perovskite NCs glass treated at a high temperature has better crystallinity, resulting in stronger nonlinear absorption performance. In addition, the value of the 2PA parameter of CsPbCl1.5Br1.5 NCs glasses decreases when the incident pump intensity increases, which is ascribed to the saturation of 2PA and population inversion. Finally, the research results show that the 2PA coefficient (0.127cmGW-1) and 3PA coefficient (1.21×10-5cm3GW-2) of CsPbCl1Br2 NCs glass with high Br anion content are larger than those of CsPbCl2Br1 and CsPbCl1.5Br1.5 NCs glasses. This is mainly due to the greater influence of Br anions on the symmetry of the perovskite structure, which leads to the redistribution of delocalized electrons. The revealed adjustable nonlinear optical properties of perovskite NCs glass are essential for developing stable and high-performance nonlinear optical devices.