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该研究成果以《Geometry symmetry-free and Higher-order Optical Bound States in the Continuum》为题发表在Nature Communication上[Nat. Commun. 12, 4390 (2021)]。苏州大学物理科学与技术学院徐亚东教授、高雷教授和南京航空航天大学伏洋洋副研究员为共同通讯作者；苏州大学物理科学与技术学院博士生周庆佳为论文的第一作者。澳大利亚新南威尔士大学Andrey Miroshnichenko教授、黄陆军博士以及中北大学吴倩楠副教授参与讨论。该工作得到了国家自然科学基金、江苏省自然科学基金、中国博士后科学基金、江苏省优势学科等项目的支持。
Femtosecond laser fabrication of controlled three dimensional structures deep in the bulk of diamond is facilitated by a dual adaptive optics system. A deformable mirror is used in parallel with a liquid crystal spatial light modulator to compensate the extreme aberrations caused by the refractive index mismatch between the diamond and the objective immersion medium. It is shown that aberration compensation is essential for the generation of controlled micron-scale features at depths greater than 200 μm, and the dual adaptive optics approach demonstrates increased fabrication efficiency relative to experiments using a single adaptive element.
This paper reviews the substantial body of literature emerging since 2004 concerning photonic nanojets. The photonic nanojet is a narrow, high-intensity, non-evanescent light beam that can propagate over a distance longer than the wavelength after emerging from the shadow-side surface of an illuminated lossless dielectric microcylinder or microsphere of diameter larger than . The nanojet’s minimum beamwidth can be smaller than the classical diffraction limit, in fact as small as ∼/3 for microspheres. It is a nonresonant phenomenon appearing for a wide range of diameters of the microcylinder or microsphere if the refractive index contrast relative to the background is less than about 2:1. Importantly, inserting within a nanojet a nanoparticle of diameter d perturbs the far-field backscattered power of the illuminated microsphere by an amount that varies as d3 for a fixed . This perturbation is much slower than the d6 dependence of Rayleigh scattering for the same nanoparticle, if isolated. This leads to a situation where, for example, the measured far-field backscattered power of a 3-m diameter microsphere could double if a 30-nm diameter nanoparticle were inserted into the nanojet emerging from the microsphere, despite the nanoparticle having only 1/10,000th the cross-section area of the microsphere. In effect, the nanojet serves to project the presence of the nanoparticle to the far field. These properties combine to afford potentially important applications of photonic nanojets for detecting and manipulating nanoscale objects, subdiffraction-resolution
nanopatterning and nanolithography, low-loss waveguiding, and ultrahigh-density optical storage.
Cell refractive index is a key biophysical parameter, which has been extensively studied. It is correlated withother cell biophysical properties including mechanical,electrical and optical properties, and not only repre-sents the intracellular mass and concentration of a cell,but also provides important insight for various biolog-ical models. Measurement techniques developed earlieronly measure the effective refractive index of a cellor a cell suspension, providing only limited information on cell refractive index and hence hindering its in-depth analysis and correlation. Recently, the emergenceof microfluidic, photonic and imaging technologieshas enabled the manipulation of a single cell and the 3D refractive index of a single cell down to sub-micronresolution, providing powerfultoolstostudycellsbasedonrefractiveindex.Inthisreview,weprovideanoverview of cell refractive index models and measurement techniques includingmicrofluidic chip-basedtechniques for the last 50 years, present the applications and significance of cell refractive index in cell biol-ogy, hematology, and pathology, and discuss future research trends in the field, including 3D imagingmethods, integration with microfluidics and potential applications in new and breakthrough research areas.
Based on full wave simulations, ∼0.3 λ and ∼0.24 λ imaging resolutions can be achieved for incoherent transverse and longitudinal point dipoles, respectively, when the dipoles are on an aluminum oxide base with a fused silica microsphere as the imaging lens. These high spatial resolutions (better than 0.5 λ) can be attributed to almost 90° light acceptance angle of the microsphere and the solid immersion effects from the microsphere/base material. These simulation results can explain the ≳0.3 λ and ≳0.24 λ minimum resolvable center to center separation distance for thin metallic nanostructures and elongated metallic nanostructures, respectively, which is equal to ≳0.1–0.14 λ edge to edge distance observed in previous microsphere imaging experiments.
From the standpoint of the wave theory, we discuss the problem of an optical image formation created by a
virtually converging electromagnetic wave from a light source. We solved a diffraction problem of a point
source in a dielectric sphere. Formulas are obtained describing the virtual image of a point source in dielectric
sphere, in the parameter range where the approximation of geometric optics is not valid. For slits in an opaque
screen, the virtual image in the dielectric sphere allows the resolution of slits spaced from each other at distances much smaller than the diffraction limit λ/2. This explains the previously obtained experimental results
[Z. B. Wang, W. Guo, L. Li, B. Luk’yanchuk, A. Khan, Z. Liu, Z. Chen, and M. H. Hong, Nat. Commun.
2, 218 (2011)] on the super resolution effect with virtual image.
Metasurfaces have recently emerged as a promising technology to realize flat and ultra-thin optical elements that can manipulate light at sub-wavelength scale. The typical design flow of a metasurface involves tedious Finite Difference Time Domain (FDTD) simulations followed by creation of a GDSII layout of the metasurface phase profile, the latter being essential for fabrication purposes. Both these steps can be time-consuming and involve the usage of expensive software. To make the design process more straightforward, we have developed an open-source software called MetaOptics built using Python for designing a generic metasurface optical element. MetaOptics uses the FDTD simulated phase response data of a set of meta-atoms and converts the phase profile of any given optical element into a metasurface GDSII layout. MetaOptics comes with in-built FDTD data for most commonly used wavelengths in the visible and infrared spectrum. It also has an option to upload user-specific dimension versus transmission phase data for any choice of wavelength. In this work we describe the software’s framework and provide details to guide users to design a metasurface layout using MetaOptics.
Advances in consumer display screen technologies have historically been adapted by researchers across the fields of optics as they can be used as electronically controlled spatial light modulators (SLMs) for a variety of uses. The performance characteristics of such SLM devices based on liquid crystal (LC) and digital micromirror device (DMD) technologies, in particular, has developed to the point where they are compatible with increasingly sensitive instrumental applications, for example, Raman spectroscopy. Spatial light modulators provide additional flexibility, from modulation of the laser excitation (including multiple laser foci patterns), manipulation of microscopic samples (optical trapping), or selection of sampling volume (adaptive optics or spatially offset Raman spectroscopy), to modulation in the spectral domain for high-resolution spectral filtering or multiplexed/compressive fast detection. Here, we introduce the benefits of different SLM devices as a part of Raman instrumentation and provide a variety of recent example applications which have benefited from their incorporation into a Raman system.
Cambridge Correlators manufacture a low-cost LC-SLM (∼ £1000) option with relatively lower specifications, which is still highly suitable for optical trapping.21
Digital micro-mirror devices (DMDs) have recently emerged as practical spatial light modulators (SLMs) for applications in photonics, primarily due to their modulation rates, which exceed by several orders of magnitude those of the already well-established nematic liquid crystal (LC)-based SLMs. This, however, comes at the expense of limited modulation depth and diffraction efficiency. Here we compare the beam-shaping fidelity of both technologies when applied to light control in complex environments, including an aberrated optical system, a highly scattering layer and a multimode optical fibre. We show that, despite their binary amplitude-only modulation, DMDs are capable of higher beam-shaping fidelity compared to LC-SLMs in all considered regimes.