Light Field Distribution Research Articles

船载激光雷达测量水体光学参数的仿真模拟研究

As an important instrument for optical observation in the water, lidar is able to efficiently obtain vertical profiles of ocean optical properties. Based on the airborne lidar model of Gordon (1982) for measuring water optical property, the processes of shipborne lidar radiative transfer and distribution of underwater light field were investigated using Monte Carlo simulation. In particular, taking into consideration receiving FOV and telescope aperture, a shipborne oceanographic lidar simulator was developed. After lidar radiative transfer was equivalent to solar radiative transfer, the simulator was validated with commonly used HydroLight which showed good coincidence. On this basis, using simulated lidar return signal, the relationships between lidar extinction coefficient α and ocean optical properties were analyzed for different observation modes and typical water bodies. The results of shipborne lidar show that with narrow receiving field of view(FOV), lidar extinction coefficient α is close to beam attenuation coefficient c, and with large receiving FOV, lidar extinction coefficient α gradually approaches to diffuse attenuation coefficient of downwelling irradiance Kd. The extinction coefficient α measured with shipborne lidar approaches to Kd slower than the airborne situation. The results of stratified water show that the α values measured in lower layer water shift towards the α values in upper layer water. The results provide the further understanding for researching the relationship between parameters measured by oceanographic lidar and ocean optical properties.

LightGAN: A Deep Generative Model for Light Field Reconstruction

A light field image captured by a plenoptic camera can be considered a sampling of light distribution within a given space. However, with the limited pixel count of the sensor, the acquisition of a high-resolution sample often comes at the expense of losing parallax information. In this work, we present a learning-based generative framework to overcome such tradeoff by directly simulating the light field distribution. An important module of our model is the high-dimensional residual block, which fully exploits the spatio-angular information. By directly learning the distribution, our approach can generate both high-quality sub-aperture images and densely-sampled light fields. Experimental results on both real-world and synthetic datasets demonstrate that the proposed method outperforms other state-of-the-art approaches and achieves visually more realistic results.

Nanoscale characterization of photonic metasurface made of lens-like SiGe Mie-resonators formed on Si (100) substrate

Submicrometer-sized high-index Mie resonators attract significant interest in photonic applications due to their capabilities to manipulate light. 2-dimensional metamaterials or metasurfaces consisting of arrays of such resonators on a device surface can be used in the flat optics, sensors, and other applications. Here, we report on the comprehensive nanoscale characterization and optical properties of nearly regular SiGe Mie resonator arrays on a Si surface fabricated using a simple and low-cost method. We achieved control on the surface morphology by depositing Ge on the Si(100) surface at elevated temperatures 890–960 °C and obtained arrays of submicrometer/micrometer low-Ge-content SiGe lenslike islands via dewetting when the Ge content was >4%. At the lower Ge content, we observed the formation of a continuous SiGe film via wetting. We used Raman microscopy not only for the Ge content and stress control but also for studying photonic properties of the islands and their coupling with the Si substrate. In contrast to the elastic light scattering, we clearly distinguished visible light Raman signals from the islands themselves and from the substrate areas under the islands enhanced compared to the signal from the open substrate. Calculation of the light electric field distribution in the islands and the substrate demonstrate how the islands trap the light and forward it into the high-index substrate. This explains the island-induced reflection suppression and Si substrate Raman enhancement, which we observe experimentally. Such an SiGe-island array is a promising metasurface for the improvement of Si photosensors and solar-energy device performance.

Backward ray tracing based high-speed visual simulation for light field display and experimental verification.

The exiting simulation method is not capable of achieving three-dimensional (3D) display result of the light field display (LFD) directly, which is important for design and optimization. Here, a high-speed visual simulation method to calculate the 3D image light field distribution is presented. Based on the backward ray tracing technique (BRT), the geometric and optical models of the LFD are constructed. The display result images are obtained, and the field of view angle (FOV) and depth of field (DOF) can be estimated, which are consistent with theoretical results and experimental results. The simulation time is 1s when the number of sampling rays is 3840×2160×100, and the computational speed of the method is at least 1000 times faster than that of the traditional physics-based renderer. A prototype was fabricated to evaluate the feasibility of the proposed method. From the results, our simulation method shows good potential for predicting the displayed image of the LFD for various positions of the observer's eye with sufficient calculation speed.

Resistance of Scratched Fused Silica Surface to UV Laser Induced Damage

Scratches in fused silica are notorious laser damage precursors to UV laser damage initiation. Ductile and brittle scratches were intentionally generated using various polishing slurries. The distribution, profile and the dimension of scratches were characterized. The damage resistance of polished surfaces was evaluated using raster scanning damage testing protocol. The results show that both ductile and brittle scratches greatly increase area proportion of laser damage about one to two orders of magnitude relative to unscratched surface and brittle scratches are more deleterious. Moreover, finite difference time domain (FDTD) simulation was used to numerically calculate the light field distribution around scratches on rear surface (i.e. exit surface for light) which indicates that modulated light intensity is susceptible to the profile and size of scratches. FDTD simulation results also indicate that the light field intensification is elevated with the dimension of scratches and light modulation effects in triangular scratches are usually not as notable as serrated and parabolic scratches.

An annular compound parabolic concentrator used in tower solar thermal power generation system

To increase the power generation efficiency of tower solar thermal power generation system, an annular compound parabolic concentrator is designed and installed at the heat receiver which is on the top of this system. The structure of the annular compound parabolic concentrator can well adapt to the light field distribution of the annular heliostat field in the system, and the solar energy reflected by heliostats can be efficiently concentrated by annular compound parabolic concentrator to the surface of the heat receiver. Using the annular compound parabolic concentrator can reduce the surface area of the heat receiver, increase the concentration ratio of the system, then raise the system’s power generation efficiency. Simulation and experimental results show that, the annular compound parabolic concentrator increases the system’s concentration ratio by about 94.4% and extend the system’s daily working hours, especially in cloudy days, so as to improve the generating efficiency by about 3 percentage points.

Realizing High-order Bessel Vortex Beams with High-level Phase Holograms

High-order Bessel beams are widely used in laser processing and precision measurement. For the realization of high-order Bessel beams, a spatial light modulator is used to load the high-order phase hologram instead of the real spiral phase plate and the axicon. The distribution of light field in two modes of axicon combination and phase superposition is analyzed theoretically. The beam modulation in two modes is designed and compared experimentally. The results show that the modulation effect of the phase superposition method is better than that of the axicon combination method. Meanwhile, the operation is flexible and the manufacture errors can be reduced. It is an effective method for realizing high-order Bessel beams.

A simple beam expanded for indoor optical wireless communication with short transmission distance

An optical wireless communication with laser light source is proposed and experimentally evaluated. We have used an arc curvature design at end-face of a piece of commercial multimode fiber (MMF) which acting as an emitting head to expand the beam diameter. The behavior of light field distributions with different emitted head were also measured and discussed. Optical amplification was carried out to compensate for the beam divergence loss in free space. The Bit error rate (BER) and launched power, measured in the distance of 2 m from ceiling to desk, are 400 Mb/s data rate and 10 dBm, respectively. The proposed method for laser expanded could be widely used in optical wireless communication system for short transmission distance.

The adjustable band gap structure and transmission characteristics for the two-dimensional function photonic crystal waveguide

In this paper, we have studied band gap structure, light field distribution, and the propagating direction in the two-dimensional function photonic crystal waveguide. For the two-dimensional function photonic crystal waveguide, the dielectric constant of dielectric column is the space coordinate function, which can be realized by the electro-optic effect and the Kerr effect. The dielectric constant function form of the dielectric column is ɛr = kr + b, the parameters k and b can be adjusted by changing the applied electric field. By changing the dielectric constant parameters k or b, we found the two-dimensional function photonic crystal waveguide transmission characteristics have the adjustability, i.e., band gap and position, defects mode number and position, the propagating direction, and light field distribution can be changed by adjusting the dielectric constant parameters k or b. It can be used to conveniently design the band gap structure, light field distribution, and the propagating direction that we need. It provides a new designed methods for optical device, such as dynamic optical device, optical switch and so on.

Nonlinear magneto optic spin Hall effect of transmitted light through a multilayer with graphene in terahertz region

Abstract We first propose the nonlinear spin Hall effect of light (SHEL) and MOSHEL (magneto optic spin Hall effect of light) through a multilayer with graphene and nonlinear substrate (NLS) in terahertz region. The MO transfer matrix method is modified to calculate the SHEL shift in a nonlinear system. The NLS brings bistable characteristics for SHEL in which nonlinear splitting of left-handed circularly polarized (LHCP) and right-handed circularly polarized (RHCP) components can be observed. The Faraday rotation of light in terahertz region causes the asymmetrical SHEL shifts distribution of LHCP and RHCP components. Meanwhile the MO effect of graphene brings modulations for nonlinear SHEL and MOSHEL which provide us new and flexible methods to control spatial light field distribution. In addition, as the delay effect causes the chaos of bistable state system, the SHEL shift can be used as a quantum point for the chaos phenomenon.

Measurement of full polarization states with hybrid holography based on geometric phase.

We propose a method for measuring the full polarization states of a light field by using hybrid polarization-angular multiplexing digital holography based on geometric phase. Through acquiring the geometric phase distribution of the whole light field by only recording a composite hologram, and according to quantitative relationship between the geometric phase and polarization state, the Stokes parameters of a light field can be calculated. Compared with other methods, this method can be used to obtain the complex amplitude information of the light field simultaneously without requiring other complex devices or elements to be adjusted, thus enabling dynamic polarization state measurement. The measurement results of the light fields generated by standard polarized optical elements, vortex half-wave retarder, and liquid crystal depolarizer verified this method's feasibility and validity.

Microlens array enhanced upconversion luminescence at low excitation irradiance.

The dearth of high upconversion luminescence (UCL) intensity at low excitation irradiance hinders the prevalent application of lanthanide-doped upconversion nanoparticles (UCNPs) in many fields ranging from optical bioimaging to photovoltaics. In this work, we propose to use microlens arrays (MLAs) as spatial light modulators to manipulate the distribution of excitation light fields in order to increase UCL, taking advantage of its nonlinear response to the excitation irradiance. We show that multicolored UCL from NaYF4:Yb3+,Er3+@NaYF4:Yb3+,Nd3+ and NaYF4:Yb3+,Tm3+@NaYF4:Yb3+,Nd3+ core/shell UCNPs can be increased by more than one order of magnitude under either 980 or 808 nm excitation, by simply placing a polymeric MLA onto the top of these samples. The observed typical green (525/540 nm) and red (654 nm) UCL bands from Er3+ and a blue (450/475 nm) UCL band from Tm3+ exhibit distinct enhancement factors due to their different multi-photon processes. Importantly, our ray tracing simulation reveals that the MLA is able to spatially confine the excitation light (980 and 808 nm) by orders of magnitude, thus amplifying UCL by more than 225-fold (the 450 nm UCL band of Tm3+) at low excitation irradiance. The proposed MLA method has immediate ramifications for the improved performance of all types of UCNP-based devices, such as UCNP-enhanced dye sensitized solar cells demonstrated here.

基于光场分布特性分析的高功率激光吸收体设计方法研究

基于光场分布特性分析的高功率激光吸收体设计方法研究

Propagation Property of an Astigmatic sin–Gaussian Beam in a Strongly Nonlocal Nonlinear Media

Based on the Snyder and Mitchell model, a closed-form propagation expression of astigmatic sin-Gaussian beams through strongly nonlocal nonlinear media (SNNM) is derived. The evolutions of the intensity distributions and the corresponding wave front dislocations are discussed analytically and numerically. It is generally proved that the light field distribution varies periodically with the propagation distance. Furthermore, it is demonstrated that the astigmatism and edge dislocation nested in the initial sin-Gaussian beams greatly influence the pattern configurations and phase singularities during propagation. In particular, it is found that, when the beam parameters are properly selected, a vortex beam with perfect doughnut-shaped profile can be obtained for astigmatic sin-Gaussian beams with two-lobe pattern propagating in SNNM.

Research on the influence of the off-axis processing axicon lens on the light field distribution of the non-diffracting beam

Non-diffracting beam are attracting increased attention because of their unique characteristics. A non-diffracting beam is usually generated with an axicon, which is a kind of line focus optical element with a conical surface axis that rotates symmetrically. Three deviation models of a generatrix relative to the ideal axicon have been established on its processing technology, namely, concave to the inner side, convex to the outer side and hyperbolic distribution of the apex of the axicon. The amplitude transmittance function is derived based on the profile of the generatrix. The emergent light field and intensity distributions of the three kinds of axicon in the case of plane wave verticality illumination are analyzed and simulated according to the Fresnel diffraction theory. Moreover, the theory of axicon diffraction field is enriched and the guiding significance for the processing of axicon lens is increased.

Generation of breathing solitons in the propagation and interactions of Airy–Gaussian beams in a cubic–quintic nonlinear medium**Project supported by the National Natural Science Foundation of China (Grant No. 51602028), the Science and Technology Development Project of Jilin Province, China (Grant No. 20160520114JH), the Youth Science Fund of Changchun University of Science and Technology, China (Grant No. XQNJJ-2017-04), and the Natural

Using the split-step Fourier transform method, we numerically investigate the generation of breathing solitons in the propagation and interactions of Airy–Gaussian (AiG) beams in a cubic–quintic nonlinear medium in one transverse dimension. We show that the propagation of single AiG beams can generate stable breathing solitons that do not accelerate within a certain initial power range. The propagation direction of these breathing solitons can be controlled by introducing a launch angle to the incident AiG beams. When two AiG beams accelerated in opposite directions interact with each other, different breathing solitons and soliton pairs are observed by adjusting the phase shift, the beam interval, the amplitudes, and the light field distribution of the initial AiG beams.

Geometric Symmetry of Dielectric Antenna Influencing Light Absorption in Quantum-Sized Metal Nanocrystals: A Comparative Study.

Silica nanoparticles, optically transparent in the visible spectral region, represent a class of dielectric antenna to tune the propagation and local field distribution of the visible light through surface scattering while the energy loss is minimized. The light scattering on the surface of silica nanoparticles include resonant scattering and random scattering that strongly depend on their geometry: spherical silica nanoparticles with the highest geometrical symmetry favors the light scattering resonances on the nanoparticle surfaces to promote resonant scattering while non-spherical silica nanoparticles mainly support random scattering. Both resonant scattering and random scattering of light on the silica nanoparticles are capable of enhancing the light absorption in quantum-sized metal nanocrystals attached to the surfaces of the silica nanoparticles. The contributions of resonant scattering and random scattering to the enhancement of light absorption have been compared and discussed. The understanding highlights the importance of the geometry of the silica nanoparticle antenna on the design and synthesis of composite materials for efficient light harvesting.

Optimized fringe removal algorithm for absorption images

Optical absorption imaging is a basic detection technique for obtaining information from matter waves, in which the absorption signal can be obtained by comparing the recorded detection light field with the light field in the presence of absorption, thereby giving the spatial distribution of the atoms. The noise in detection arises mainly from differences between the two recorded light field distributions, which is difficult to avoid in experiments. In this work, we present an optimized fringe removal algorithm, developing a method to generate an ideal reference light field, avoiding the noise generated by the light field difference, and suppressing the noise signal to the theoretical limit. Using principal component analysis, we explore the optimal calculation area and how to remove noise information from the basis to allow optimal performance and speed. As an example, we consider scattering atomic peaks with a small number of atoms in a triangular lattice. Compared with the conventional processing method, our algorithm can reduce the measured atomic temperature variance by more than three times, giving a more reliable result.

Large depth focus-tunable photoacoustic tomography based on clinical ultrasound array transducer

Multi-element photoacoustic tomography systems have either a non-movable focus or a non-uniform light field distribution over the region of interest, significantly limiting the depth-of-field and resolution of images. In this study, focus-tunable photoacoustic tomography (FT-PAT) based on a clinical ultrasound array transducer with uniform laser excitation was developed to achieve high-resolution imaging in deep tissue. An adjustable line-focusing structure was used to condense the laser beam, and the excited photoacoustic signal was processed via a synthetic-aperture focusing technique. Carbon rods at different depths were used to evaluate the focus-tunable ability in a tissue phantom. In vivo focus-tunable imaging performance was demonstrated by an experiment involving imaging of carbon nanoparticle-labeled living nude mouse covered by chicken breast. The signal-to-noise ratio of targets at different depths was changed by focus adjustment, which demonstrates that the FT-PAT system has potential clinical applications in deep tumor imaging and subsequent diagnoses.

Validation of vectorial theories for the focusing of high numerical aperture Fresnel zone plates

Abstract To study the applicability of vectorial angular spectrum (VAS) theory and vectorial Debye–Wolf diffraction integral for the focusing of high numerical aperture (NA) Fresnel Zone Plates (FZPs), these two vectorial methods have been rigorously examined by the three-dimensional finite-difference time-domain (FDTD) method under general and specific conditions. It is found that for a low total annulus number and when the wavelength dispersion or obstruction are existing, Debye–Wolf diffraction integral has failed to describe the light field distribution in the focal region. On the contrary, VAS theory can generally predict the focusing properties. However, when a FZP only contains one or two transparent annuli, both VAS and Debye–Wolf diffraction theories are invalid. Wavelength dispersion and purpose obstruction can produce the multi-focus or focal shift, which can be used for the axial wavelength scanning, the precise measurement of laser wavelength, or optical trapping.