- 标题
- 摘要
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- 实验方案
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Characterizing daytime wind profiles with the wide-field Shack–Hartmann wavefront sensor
摘要： Knowledge of the vertical spatio-temporal distribution of the wind speed and direction is essential for optimizing the performance of adaptive optics systems. An extension of SLODAR (slope detection and ranging) can be used for wind profiling by tracking the time-delayed cross-correlation peaks obtained from the slope of the Shack–Hartmann wavefront sensor. This wind-profiling method works well in situations where the cross-correlation peaks can be individualized, but in many cases the isolated cross-correlation peaks for each turbulent layer are difficult to find in the 2D cross-correlation maps, which can result in difficulties when estimating the wind profiles. To address this problem, we propose a method to measure the wind speed and direction of each layer. The method distinguishes isolated peaks more easily and is valid for multiple peaks, even for a weak response. Instead of tracking peaks in 2D cross-correlation maps, the proposed method traces a series of cross-correlation peaks in the curves of 1D slices through the maps from different directions, and finally determines the wind speed and direction according to the frozen-flow hypothesis. This method is verified with simulations, in which the input wind profiles are recovered accurately. Furthermore, this method is applied to 47 data sequences from the 1-m New Vacuum Solar Telescope at Fuxian Solar Observatory. The wind profiles are estimated from the ground up to 12 km, and the experimental results show that all layers move with a relatively low speed.
关键词： Sun: granulation,atmospheric effects,instrumentation: adaptive optics
更新于2025-09-23 15:23:52
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Contact Lenses || Optics and Lens Design
摘要： Some aspects of contact lens design and optics are rarely applied nowadays, as they are less relevant to modern practice, but readers may still need to refer to them. They are available at: https://expertconsult.inkling.com/, whereas the more relevant topics are included here. The appendix, available at: https://expertconsult.inkling.com/, also describes various equations that are used in contact lens work, while the online resources include programs relating to both the optics and to lens design. There are two main aspects to be considered when dealing with the optics of contact lenses: the effects on the wearer of the optical differences from spectacles and the necessity for the practitioner to understand the components which affect the back vertex power (BVP) of the contact-lens/liquid*-lens system. There is some overlap of these two aspects, but for the sake of convenience they are discussed separately in the first two sections of the chapter. In the second section a set of approximate rules is included, the use of which should permit practitioners to make quick and reasonably accurate estimates of changes in power caused by altering certain lens parameters. The Cartesian sign convention2 is used throughout. For further understanding of the basic principles involved, readers are referred to the works of Bennett (1985), Tunnacliffe (1993), Freeman and Hull (2003), Douthwaite (2006) and Rabbetts (2007).
关键词： Lens Design,Astigmatism,Optics,Bifocal Contact Lenses,Power Variations,Contact Lenses,Ocular Refraction,Aberrations,Spectacles
更新于2025-09-23 15:23:52
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Influence of experimental parameters on linear, nonlinear optical and ultrafast dynamics properties of In doped ZnO nanorods
摘要： In-doped ZnO (IZO) nanorods have been successfully synthesized by chemical vapour deposition method. The structure, morphology and linear optical properties of IZO nanorods have been characterized. The excitation intensity and temperature - dependent the photoluminescence of IZO nanorods were analyzed. The nonlinear optical absorption properties were studied by using the Z-scan technique with same wavelengths at different laser pulses and energies. IZO nanorods showed two-photon absorption (TPA) mechanism at 532 nm. In the low-energy pulse regime, IZO nanorods showed TPA induced ground state saturable absorption (SA). However, with increasing the energy pulse regime, an apparent TPA induced reverse-saturable absorption (RSA) was observed. The ultrafast dynamics properties of IZO nanorods were investigated by the pump-probe technique under different laser parameters. The femtosecond transient absorption spectra show that the few decades picosecond component has been assigned to the shallow donor mixed with donor bound recombination, and the slowed components represent the decay from donor–acceptor pair recombination.
关键词： Zinc oxide,Nonlinear optics properties,Photoluminescence,Chemical vapour deposition
更新于2025-09-23 15:23:52
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Nonlinear Diffraction in Asymmetric Dielectric Metasurfaces
摘要： Metasurfaces provide new and promising mechanisms to control and manipulate light at the nanoscale. While most metasurfaces are designed to operate in the linear regime, it was recently shown that such metasurfaces may also generate nonlinear signal, by manipulating the higher order susceptibility terms. As such, metasurfaces can generate additional harmonics, without the need for light propagation, as typically occur in nonlinear crystals. While such demonstrations typically rely on the nonlinear properties of metals, we hereby report the design, fabrication and experimental characterization of a resonant dielectric metasurface made of amorphous silicon to create and manipulate second harmonic light and control its diffraction patterns. As shown in the paper, the second harmonic generation of light follows selection rules which rely on the asymmetry of the meta-atom. Given the fact that silicon crystals are centrosymmetric, the generation of second harmonic signal in amorphous silicon is intriguing. In fact, second harmonic signal is generated mostly from the surface of the meta atom. It is the use of nanostructures that increases the surface to volume ratio and enables second harmonic generation. Additionally, the meta atom is designed to exploit its spectral resonances in the principal and the second harmonic frequencies for providing electromagnetic field enhancement which assist in boosting up the generation of second harmonic signal.
关键词： Metasurfaces,Nonlinear optics,Dielectric metasurfaces,Phase gradient metasurfaces
更新于2025-09-23 15:23:52
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Spin-Selective Transmission in Chiral Folded Metasurfaces
摘要： Controlling the spin angular momentum of light (or circular polarization state) plays a crucial role in the modern photonic applications such as optical communication, circular dichroism spectroscopy, and quantum information processing. However, the conventional approaches to manipulate the spin of light require naturally occurring chiral or birefringent materials of bulky sizes due to the weak light-matter interactions. Here we experimentally demonstrate an approach to implement spin-selective transmission in the infrared region based on chiral folded metasurfaces that are capable of transmitting one spin state of light while largely prohibiting the other. Due to the intrinsic chirality of the folded metasurface, a remarkable circular dichroism as large as 0.7 with the maximum transmittance exceeding 92% is experimentally demonstrated. The giant circular dichroism is interpreted within the framework of charge-current multipole expansion. Moreover, the intrinsic chirality can be readily controlled by manipulating the folding angle of the metasurface with respect to the cardinal plane. Benefiting from its strong chirality and spin-dependent transmission characteristics, the proposed folded metasurface may be applied to a range of novel photon-spin selective devices for optical communication technologies and bio-photonics.
关键词： sub-wavelength optics,Folded metasurface,intrinsic chirality,spin-selective transmission
更新于2025-09-23 15:23:52
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In Vivo Rat Brain Imaging through Full-Field Optical Coherence Microscopy Using an Ultrathin Short Multimode Fiber Probe
摘要： We demonstrate full-field optical coherence microscopy (OCM) using an ultrathin forward-imaging short multimode fiber (SMMF) probe with a core diameter of 50 μm, outer diameter of 125 μm, and length of 7.4 mm, which is a typical graded-index multimode fiber used for optical communications. The axial and lateral resolutions were measured to be 2.14 μm and 2.3 μm, respectively. By inserting the SMMF 4 mm into the cortex of an in vivo rat brain, scanning was performed to a depth of 147 μm from the SMMF facet with a field of view of 47 μm. Three-dimensional (3D) OCM images were obtained at depths ranging from approximately 20 μm to 90 μm. Based on the morphological information of the resliced 3D images and the dependence of the integration of the OCM image signal on the insertion length, the obtained 3D information of nerve fibers has been presented.
关键词： medical optics instrumentation,full-field optical coherence microscopy,endoscopic imaging,fiber optics imaging
更新于2025-09-23 15:22:29
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Smart Optical Catheters for Epidurals
摘要： Placing the needle inside the epidural space for locoregional anesthesia is a challenging procedure, which even today is left to the expertise of the operator. Recently, we have demonstrated that the use of optically sensorized needles significantly improves the effectiveness of this procedure. Here, we propose an optimized configuration, where the optical fiber strain sensor is directly integrated inside the epidural catheter. The new design allows the solving of the biocompatibility issues and increases the versatility of the former configuration. Through an in vivo study carried out on a porcine model, we confirm the reliability of our approach, which also opens the way to catheter monitoring during insertion inside biological spaces.
关键词： medical optics instrumentation,fiber optics sensors,clinical applications,fiber Bragg gratings
更新于2025-09-23 15:22:29
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Optical matching of a multimode gradient fibre and single-mode stepped-index fibre in a photopolymerizable composition
摘要： The opportunity to optically match waveguides characterized by an essentially different field structure in a photopolymerizable medium is investigated. The example of a multimode gradient fibre (core diameter 50 μm) and a single-mode stepped-index fibre SMF-28 (core diameter 8.2 μm) shows that the efficiency of radiation transmission from the wide fibre into the narrow one can reach 60% at a distance between their end faces of about 900 μm.
关键词： nonlinear optics,photopolymer,optical matching of fibres,fibre optics,laser radiation
更新于2025-09-23 15:22:29
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[IEEE 2018 International Conference on Intelligent and Innovative Computing Applications (ICONIC) - Mon Tresor, Plaine Magnien, Mauritius (2018.12.6-2018.12.7)] 2018 International Conference on Intelligent and Innovative Computing Applications (ICONIC) - Climatic Effects on Free Space Optics Link: South African Climate
摘要： The growth in demand of high data rate, reliable quality of service, low cost technology and secured connectivity have been telecommunication users' concerns. Free Space Optics (FSO) is the best choice for meeting these demands as it offers data rates in Gbps with the most secure communication because light beam is prone to eavesdropping. However, usage of FSO as a communication link relies upon local weather condition. Atmospheric attenuation of fog, rain and snow are the most limitation of free space optic availability, as they lead to the diminution of limited available bandwidth. This paper investigated the link performance under climatic conditions such as fog, rain and snow by at various wavelengths of 650nm, 750nm, 850nm, 950nm and 1550nm. It is further deals with FSO performance targeting to acquire minimal Bit Error Rate (BER), suitable transmitting power, optimum link margin and reliable data transmission rate at maximum link distance of 1km. The studies observed that received power signal and the link distance have an inverse correlation because once the signal reaches to an extended distance; it faces greater climatic attenuation due to scattering and absorption lessening.
关键词： communication link,Free space optics,atmospheric attenuation,light beam,bit error rate
更新于2025-09-23 15:22:29
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[IEEE 2017 IEEE International Conference on Space Optical Systems and Applications (ICSOS) - Naha (2017.11.14-2017.11.16)] 2017 IEEE International Conference on Space Optical Systems and Applications (ICSOS) - Adaptive optics pre-compensation for GEO feeder links: Towards an experimental demonstration
摘要： High throughput ground to satellite telecommunication systems will require very capacitive links for the uplink. When diffraction limited, a few optical Watts per channel are sufficient to close the link budget. In the presence of atmospheric turbulence, higher emission powers are necessary to cope with the subsequent disruptions of the beam. Pre-compensation by adaptive optics has been identified as a key strategy to keep the requested power at reasonable levels. However limited by point-ahead anisoplanatism. Fine trade-offs shall be carried out to overcome this limitation while considering the specificities of optical telecommunication requirements (low fading probably, short fading duration, manageable cost and complexity). The expected performance of the pre-compensation by adaptive optics for optical feeder links is investigated through numerical simulations. A ground-to-ground experimental demonstration is proposed. The selected slant line of sight and the beam geometry is shown to induce turbulence effects, including angular decorrelation, that are representative of the GEO feeder link scenario when considering an appropriate setup.
关键词： anisoplanatism,adaptive optics,ground to satellite laser links
更新于2025-09-23 15:22:29