Uniform Spot Research Articles

Constraining the properties of the thermonuclear burst oscillation source XTE J1814-338 through pulse profile modelling

Abstract Pulse profile modelling (PPM) is a comprehensive relativistic ray-tracing technique employed to determine the properties of neutron stars. In this study, we apply this technique to the Type I X-ray burster and accretion-powered millisecond pulsar J, extracting its fundamental properties using PPM of its thermonuclear burst oscillations. Using data from its 2003 outburst, and a single uniform temperature hot spot model, we infer J to be located at a distance of $7.2^{+0.3}_{-0.4}$ kpc, with a mass of $1.21^{+0.05}_{-0.05}$ M⊙ and an equatorial radius of $7.0^{+0.4}_{-0.4}$ km. Our results also offer insight into the time evolution of the hot spot but point to some potential shortcomings of the single uniform temperature hot spot model. We explore the implications of this result, including what we can learn about thermonuclear burst oscillation mechanisms and the importance of modelling the accretion contribution to the emission during the burst.

Broadband achromatic thermal metalens with a wide field of view based on wafer-level monolithic processes

We present a monolithic metalens free of chromatic aberration over the 8–12 μm wavelength range for thermal imaging. The metalens consists of nano-donut-pillars for dispersion engineering. The proposed metalens design is based on a telecentric optical system, which effectively eliminates off-focus distortion and aberration, enhancing overall imaging quality. Offering a 90° field of view, the metalens ensures uniform focal spot sizes within a 45° field angle across the working wavelength. This enables the capture of high-quality thermal images with sharp images and minimal distortion. With a diameter of 5.75 mm, the metalens is suitable for integration into commercial thermal imaging cameras. The nano-donut-pillar structure of the metalens allows for relatively straightforward mass production, involving i-line stepper lithography and silicon deep etching processes.

Power Enhancement and Spot Homogenization Design for Arrayed Semiconductor Lasers.

Improving the spot brightness and uniformity of arrangement of the array laser is conducive to ensuring the beam quality of the fiber laser. Based on the light tracing principle, the optical model performance of two common fiber lasers was first analyzed. Then, a novel rotationally polarized optical model with high power and spot uniformity was designed and optimized on the basis of the aforementioned analysis. The results of the evaluation metrics of the multi-indicator optical model show that the spot uniformity of our proposed model improved by 24.03%, the power improved by 0.55%, and the maximum light distance was shortened from 120 mm to 82.58 mm. Further, the results of the coupling tolerance analysis of the optical elements show that the total coupling efficiency was 89.04%. The coupling power and tolerance relationships did not produce degradation compared with the traditional model. Extensive comparative results show that the designed rotationally polarized optical path model can effectively improve the optical coupling efficiency and spot uniformity of arrayed semiconductor lasers.

Generation of needle-shaped beam with super-resolution spot and large depth of focus using diffractive optics

The finite depth of focus (DOF) of a focusing lens gives rise to the degradation of lateral resolution at defocused positions. Consequently, the generation of a needle-shaped beam with sub-diffraction size and extended DOF can break through this limitation, but few studies have effectively balanced these two characteristics. In this paper, we propose a method based on the stochastic parallel gradient descent (SPGD) algorithm for designing multi-ring diffractive optical elements (DOEs) to produce the needle-shaped beam, which maintains a super-resolution and uniform spot within a large extended DOF range. Numerical simulations and experimental results have validated that our method can extend the DOF by 14 times longitudinally and reduce the lateral resolution to 73% of Airy spot, while maintaining up to 92% uniformity of the beam diameter. Furthermore, we demonstrate that the DOF of the needle-shaped beam extends with the increase of the number of rings and phase levels within the DOE. Our work provides an effective strategy for the design of DOF-extended DOE and it is anticipated to find potential applications in microscopy and three-dimensional imaging, photolithography, and optical manipulation.

Dual-path coupling V-shaped structure off-axis integrated cavity output spectroscopy (V-OA-ICOS) for water vapor stable isotope detection at 3.66 μm

Residual cavity mode noise and weak output signal are the main factors that restrict the detection performance of off-axis integrated cavity output spectroscopy (OA-ICOS). In order to overcome the above drawbacks, a novel V-shaped off-axis integrated cavity output spectroscopy (V-OA-ICOS) device was demonstrated, and the dual-path coupling method was further proposed. The dual-path coupling V-OA-ICOS device can not only suppress the residual cavity mode noise but also enhance the intensity of the output signal. The V-shaped resonator cavity ensures a more uniform and square-shaped spot pattern distribution on the surface of the highly reflective mirrors, significantly reducing spots overlap. The dual-path coupling method can re-couple the laser reflected by the front cavity mirror, thereby increasing the total energy and mode density of the cavity. The spectrum of water vapor stable isotopes HD16O and H216O at 3.66 μm was measured to illustrate the performance of the presented approach, the dual-path coupling V-OA-ICOS increases the signal-to-noise ratio (SNR) by a factor ∼ 2.1 compared to single path V-OA-ICOS and the signal intensity by a factor of ∼ 2. The δD variation was obtained by measuring the outdoor water vapor isotope using this device for three consecutive days. The variation range of δD is −220‰ ∼ −120‰. This work proposes a new cavity structure and optical re-coupling method, which offers a novel approach to enhance the performance of OA-ICOS devices.

3D cell subculturing pillar dish for pharmacogenetic analysis and high-throughput screening

A pillar dishe for subculture of 3D cultured cells on hydrogel spots (Matrigel and alginate) have been developed. Cells cultured in 3D in an extracellular matrix (ECM) can retain their intrinsic properties, but cells cultured in 2D lose their intrinsic properties as the cells stick to the bottom of the well. Previously, cells and ECM spots were dispensed on a conventional culture dish for 3D cultivation. However, as the spot shape and location depended on user handling, pillars were added to the dish to realize uniform spot shape and stable subculture, supporting 3D cell culture-based high-throughput screening (HTS). Matrigel and alginate were used as ECMs during 6-passage subculture. The growth rate of lung cancer cell (A549) was higher on Matrigel than on alginate. Cancer cell was subcultured in three dimensions in the proposed pillar dish and used for drug screening and differential gene expression analysis. Interestingly, stemness markers, which are unique characteristics of lung cancer cells inducing drug resistance, were upregulated in 3D-subcultured cells compared with those in 2D-subcultured cells. Additionally, the PI3K/Akt/mTOR, VEGFR1/2, and Wnt pathways, which are promising therapeutic targets for lung cancer, were activated, showing high drug sensitivity under 3D-HTS using the 3D-subcultured cells.

Non-iterative phase-only modulation method for generating high-uniformity 3D multifocal spots with flexible position control

We propose a non-iterative wavefront phase computation method, the crescent segmentation phase (CSP) method that generates 3D multifocal spots with flexible control over their positions. Previously reported segmentation-based work usually introduces diffraction stray light mainly caused by the periodic structures of regional design. Our method reduces the stray light and obtains higher spot uniformity through a simple and effective phase pattern division process. Then we apply the CSP method to the approach of point spread function (PSF) modulation designed for stimulated emission depletion (STED) microscopy. A new phase generation method is proposed that can achieve simultaneous PSF modulation in both lateral and axial directions with only one phase modulation. Our CSP method is suitable for spatial light modulators (SLMs). Furthermore, our approach has potential applications in the fields of laser direct writing, optical data storage, super-resolution imaging, and optogenetics.

Beam shaping for two-dimensional laser array by a computational model

The application of two-dimensional array laser source is more and more popular. Currently, many methods have been proposed for the collimation of laser beams; however, there is still a lack of research for the collimation of array laser sources so far. This paper presents a collimating method for array laser source. Through the calculation of the lens surfaces, the shape of the illumination spot on the target can be directly controlled, and the diameter of the lens can be directly constrained by setting the initial point coordinates. In this method, the edge-ray principle is used to simplify the extended light source model. The size and intensity distribution of the light spot irradiated by the light source to the target position were simulated by establishing a ray tracing model. The whole process was calculated using MATLAB software. The corresponding lens model can be obtained by fitting discrete coordinate points using Solid Works. Finally, the optical design software ZEMAX is used for simulation test. After shaping the laser light source with a luminous diameter of 1 mm, a circular and uniform spot is obtained at 100 m. For the point light source model, the divergence angle of 0.28° is achieved. Furthermore, an annular spot is also realized by setting the laser irradiation range, which provide a new solution for customized laser lighting.

Optical design of a monolithic compressed folding imaging lens for infrared/laser dual-band.

In order to realize the miniaturization of the dual-band system, the monolithic compressed folding imaging lens (CFIL) is designed for infrared/laser dual-band in this paper. The relationship among the back focal length, field of view, pupil diameter, and central obscuration of the CFIL are derived. The design method of the dual-band CFIL is given, and the stray light of the CFIL can be suppressed by the double-layer hood structure. According to the design method of the CFIL, the infrared/laser dual-band can be applied by a monolithic optical element. The design results show that the minimum MTF for all fields of view in the infrared band is greater than 0.125 at 42lp/mm, the spot uniformity in the laser band is greater than 90%, and the total system length is only 0.305 times the focal length. After tolerance analysis, the MTF of CFIL is greater than 0.1, and the spot diagram is less than 880µm. The working temperature of the system is -20∼50°C, and the compensation distance is given. After stray light optimization, The point source transmittance (PST) value in the infrared band is reduced by 2 to 4 orders of magnitude, and the PST value in the laser band is reduced by 1 to 5 orders of magnitude. Compared with the traditional coaxial reflective system, the infrared/laser dual-band CFIL has only one lens, and the optical structure is compact. It provides a new idea for the integration and miniaturization of the multi-band system.

Design and Analysis of Comprehensive Solar Utilization System Based on Photovoltaic Concentration and Spectral Splitting

In order to address the issue of a solar utilization system with low efficiency, this paper designs a new solar conversion system based on photovoltaic concentration and spectral splitting. The system concentrates sunlight through a Fresnel lens and uses a hollow concave cavity to evenly distribute the incident energy flow. The spectral splitting medium separates the useful irradiance for the PV cell from those wavelengths that are more suited to heat generation. By considering the available wavelength of photovoltaic cells, the GaAs cell and a ZnO nanofluid were selected for this paper. It was found that installing the hollow concave cavity improved the spot uniformity of the PV cell surface by 17%. The output efficiency of the system under various circumstances was analyzed. The results show that at a concentration ratio of 50 and a light intensity of 1000 W/m2, photoelectric conversion efficiency increased by 0.81%. When compared to direct concentration, the photoelectric conversion efficiency increased by at least 7%. Meanwhile, the comprehensive electrical efficiency was 36.7%, which is higher than that of the normal concentration PV and comprehensive thermal system.

Statistical spatial properties of a light field on a target plane

Studying the light field characteristics of a target plane is critical in controlling the laser-plasma instability (LPI), which is necessary to increase laser energy utilization and compression symmetry in high-power laser facilities. In this study, a statistical method is used to analyze the transmission light characteristics of a target plane for single and multiple beams. We reconstructed the light transmission model on the target plane and analyzed the relationships between the focal spot width and incidence angle, and speckle width and incidence angle using the autocorrelation function. In addition, the relationship between the interference pattern and incident beams is obtained by deriving the beam superposition theory. The results show that the speckle and focal spot widths are stretched in the direction in which the incident plane projects. The direction of the interference structure generated by multiple-laser beams is perpendicular to the line joining of the sub-beams, and the period is related to both wavelength and incidence angle. Experimental results are consistent with the theoretical analysis. The influence of incident beam number on the focal spot uniformity is also studied. The results are of great significance for regulating the sub-beam incidence direction, understanding light properties to further improve focal spot uniformity and suppress the LPI.

Random Silica-Glass Microlens Arrays Based on the Molding Technology of Photocurable Nanocomposites

Random microlens arrays (rMLAs) have been widely applied as a beam-shaping component within an optical system. Silica glass is undoubtedly the best choice for rMLAs because of its wide range of spectra with high transmission and high damage threshold. Yet, machining silica glass with user-defined shapes is still challenging. In this work, novel design and fabrication methods of random silica-glass microlens arrays (rSMLAs) are proposed and a detailed investigation of this technology is presented. Based on the molding technology, the fabricated rSMLAs with tunable divergent angles demonstrate superior physical properties with 1.81 nm roughness, 1074.33 HV hardness, and excellent thermal stability at 1250 °C for 3 h. Meanwhile, their characterized optical performance shows a high transmission of over 90% in the ultraviolet spectrum. The fabricated two types of rSMLAs exhibit excellent effects of beam homogenization with surprising energy utilization (more than 90%) and light spot uniformity (more than 80%). This innovative process paves a new route for fabricating rMLAs on solid silica glass and breaking down the barrier of rMLAs to broader applications.

All-in-One Collimating Splitter Based on a Meta-Fiber Platform

The use of array generators has become ubiquitous in various applications such as laser fabrication, face identification, and motion sensing. The Dammann grating, a diffractive optical element, is the mainstream approach for generating uniform spot arrays. However, its limited capability and the contradiction between the performance and the complexity of fabrication hinder its application. To address this issue, an all-in-one collimating splitter based on metasurfaces is theoretically proposed by synthesizing the phase of an inverse-optimized Dammann grating and a collimating lens. Leveraging both the diffraction effect of Dammann grating and the Fourier transformation of the collimating lens, the number of spot arrays can be largely increased with a single lenslet. The proposed design shows a large field of view of 62° × 62° and a high uniformity of 1.29% in generating a spot array of 3 × 3 on a single-fiber platform, confirmed by both the scalar and full-wave simulation. Further, a larger spot array up to 15 × 15 is also derived in the far field by integrating the proposed metasurface on a 5 × 5 fiber array platform, confirmed by the scalar simulation. Our design may be transplanted to the vertical-cavity surface-emitting laser platform, and shows great potential in various applications including face identification and motion sensing.

A novel non-confocal two-stage dish concentrating photovoltaic/thermal hybrid system utilizing spectral beam splitting technology: Optical and thermal performance investigations

Concentrating and spectral beam splitting technology towards the efficient utilization of full-spectrum solar energy has been widely concerned. This paper proposes a novel non-confocal two-stage parabolic dish concentrating photovoltaic/thermal (NTPD-CPVT) hybrid system which offers access to the alleviation of photovoltaic heat load and the two-stage heating of heat transfer fluid through a specially developed spectral beam splitter. The thermodynamic and optical properties of the system are analyzed via the comprehensive model including ray tracing, energy flux evaluation and photovoltaic/thermal hybrid energy evaluation. Results indicate that the satisfied spot uniformity and optical efficiency of 80.7% could be obtained by non-confocal optimization, and the NTPD-CPVT hybrid system shows stable overall energy efficiency over 20.9% under different irradiance conditions. Based on the comprehensive comparison, the introduction of a spectral beam splitter promotes the photovoltaic/thermal module efficiency and the system exergy efficiency by 17.6% and 10.2%, and effectively shortens the payback period. Furthermore, the reference values of implemental parameters such as error tolerances and heat transfer coefficients are provided to guarantee the optical and economic performance of the system. The research results support the potential of the NTPD-CPVT hybrid system in improving the cascade use of solar spectrum and guide the construction of future prototypes.

Design of DOE Based on Modified GS Algorithm for Preparation of Micron‑Scale Uniform Light Spot in Ultraviolet Band

Design of DOE Based on Modified GS Algorithm for Preparation of Micron‑Scale Uniform Light Spot in Ultraviolet Band

Experimental and numerical study regarding the biomimetic bone porous structure to match energy and mass flow in a solar thermochemical reactor

In the methane dry reforming driven by concentrated solar energy, the challenges that restrict efficient solar energy conversion mainly include regulating the solar energy to match the solar thermochemical reaction on-demand, optimization of catalytic carrier structures and preparation of high-performance catalysts. The mismatch between energy and flow in a thermochemical reactor has important consequences for solar energy storage efficiency. To improve the solar thermochemical performance, the idea of using a biomimetic bone porous structure as a catalyst carrier is proposed to achieve flow and energy matching in a thermochemical reactor. The methods of Monte Carlo ray tracing and user-defined functions are used to establish thermochemical analysis model. A solar heat flux experimental system is built to determine the real concentrated solar heat flux. The effects of different pore size combinations and Gaussian-like inlet flow on the methane reforming performance are studied. The experiment system obtains a uniform light spot of 40 mm at Pe = 7.0 kW with the peak flux density of 3086.73 kW/m2. The results indicate that by the introduction of a biomimetic bone porous structure to optimize flow and energy matching, the energy storage efficiency and methane conversion rate can be improved by 2.17 % and 8.97 %, respectively. This research provides a novel approach for efficient solar energy conversion and storage in solar thermochemical reactor.

Full-aperture random polarization smoothing for a low-coherence laser facility.

Two new random polarization smoothing methods using full-aperture elements are proposed on low-coherence lasers, one using birefringent wedge and one using flat birefringent plate. By designing the crystal axis direction and wedge angle of the birefringent plates, the methods can selectively introduce time delay and spatial displacement, so as to obtain fast random evolution of transient polarization by utilizing low spatiotemporal coherence of the laser focal field. Both methods avoid the near field discontinuity and can be used under high fluence. The method using birefringent wedge can slightly improve focal spot uniformity, and the method using flat birefringent plate can obtain non-polarization with DOP lower than 2%. Theoretical studies show that the resulting focal polarization evolves rapidly on sub-picosecond timescales and rapidly covers the entire Poincaré sphere. The method using birefringent wedge is achieved in experiment. The results show that the degree of polarization of the focal spot is reduced from 1 to 0.27, which proves the effectiveness of the full-aperture random polarization smoothing. The full-aperture random polarization smoothing can generate a focal field very close to unpolarized thermal light, which is expected to suppress the laser plasmas instability.

Freeform Optical Design of Smooth Hermite Radial Basis Function Implicit Surface under Point-Normal Constraints

The freeform surface has become a primary optical design method due to its higher degree of freedom, and the quadratic supporting method is one of the mainstream methods of freeform optical design because of its inherent integrability. Nevertheless, the quadratic supporting surface is usually not smooth, and its smooth enveloping surface needs to be further solved to satisfy the optical manufacturing requirements. The sampling value points and corresponding unit normal vectors on the quadratic supporting surface are used as constraints, and the implicit surface method based on the Hermite radial basis is adopted to successfully generate a smooth freeform optical surface that can project a uniform square spot on the target screen. The point-normal constraints are optimized in terms of value point interpolation and increasing the supporting sub-surface array. And the optical simulation results show that proposed algorithm has more minor errors of value point and normal vector, and better shapes the light beam.

Market-Based Redispatch May Result in Inefficient Dispatch

In this paper we analyze a uniform price day-ahead electricity spot market that is followed by redispatch in the case of network congestion. We assume that the transmission system operator is incentivized to minimize redispatch cost and compare cost-based redispatch (CBR) to market-based redispatch (MBR) mechanisms. For networks with at least three nodes we show that in contrast to CBR, in the case of MBR incentives to minimize redispatch cost are in general not efficient in the context of our short-run analysis. This obtains both for pay-as-bid as well as locational marginal prices used for MBR compensation. As we demonstrate, moreover, in case of MBR the possibility of the transmission system operator to inefficiently reduce redispatch cost at the expense of decreased overall welfare can be driven both by the electricity supply side and the electricity demand side.Our results highlight a novel and important aspect regarding the design and the desirability of congestion management regimes in liberalized electricity markets.

Nanoscale Valley Modulation by Surface Plasmon Interference.

Excitons in two-dimensional (2D) materials have attracted the attention of the community to develop improved photoelectronic devices. Previous reports are based on direct excitation where the out-of-plane illumination projects a uniform single-mode light spot. However, because of the optical diffraction limit, the minimal spot size is a few micrometers, inhibiting the precise manipulation and control of excitons at the nanoscale level. Herein, we introduced the in-plane coherent surface plasmonic interference (SPI) field to excite and modulate excitons remotely. Compared to the out-of-plane light, a uniform in-plane SPI suggests a more compact spatial volume and an abundance of mode selections for a single or an array of device modulation. Our results not only build up a fundamental platform for operating and encoding the exciton states at the nanoscale level but also provide a new avenue toward all-optical integrated valleytronic chips for future quantum computation and information applications.