Fan Zetao, You Xinxiang, Zhang Douguo
Advanced Laser Technology Laboratory of Anhui Province, Department of Optics and Optical Engineering, University of Science and Technology of China, Hefei, Anhui 230026, China.
Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China.
Proc Natl Acad Sci U S A. 2025 Feb 25;122(8):e2423223122. doi: 10.1073/pnas.2423223122. Epub 2025 Feb 20.
Dark-field microscopy is a technique used in optical microscopy to increase the contrast in unstained samples, making it possible to observe details that would otherwise be difficult to see under bright-field microscopy; thus, it has been widely employed in biological research, material science, and medical diagnostics. However, most dark-field microscopy methods cannot overcome the optical diffraction limit and require a bulky dark-field condenser and precise alignment of each optical element. In this study, we introduce a planar photonic device that can produce random speckles for dark-field illumination and improve the optical resolution. This planar device is made of random distribution fibers for injection of a laser beam, a scattering layer to produce random speckles, a one-dimensional photonic crystal (1DPC) to produce a hollow cone of light, and a metallic film to increase the energy efficiency. This planar device can work as a substrate for conventional microscopy. Taking advantage of the hollow cone of light with random speckles generated by the proposed planar device, we achieve a high-contrast, label-free image with a 1.55-fold improvement in spatial resolution. Furthermore, random evanescent speckles can be generated on the 1DPC just through tuning the incident wavelength, which demonstrates the ability for optical surface imaging beyond the diffraction limit. The advantage of this technique is that it does not require complex optical system or precise knowledge of the illumination pattern. This study will expand the potential applications of dark-field microscopy and provide insights into samples that might otherwise be invisible under traditional dark-field microscopy.
暗场显微镜是光学显微镜中使用的一种技术，用于增加未染色样品的对比度，使观察在明场显微镜下难以看到的细节成为可能；因此，它已广泛应用于生物学研究、材料科学和医学诊断。然而，大多数暗场显微镜方法无法克服光学衍射极限，并且需要一个庞大的暗场聚光镜和每个光学元件的精确对准。在本研究中，我们介绍了一种平面光子器件，它可以产生用于暗场照明的随机散斑并提高光学分辨率。该平面器件由用于注入激光束的随机分布光纤、用于产生随机散斑的散射层、用于产生空心光锥的一维光子晶体（1DPC）以及用于提高能量效率的金属膜组成。该平面器件可以用作传统显微镜的基板。利用所提出的平面器件产生的带有随机散斑的空心光锥，我们获得了高对比度、无标记的图像，空间分辨率提高了1.55倍。此外，仅通过调整入射波长就可以在1DPC上产生随机倏逝散斑，这证明了超越衍射极限进行光学表面成像的能力。该技术的优点是不需要复杂的光学系统或对照明图案的精确了解。这项研究将扩大暗场显微镜的潜在应用，并为在传统暗场显微镜下可能不可见的样品提供见解。
