Spatial Intensity Distribution Research Articles

Effect of laser ablation angles on the ablated depth/mass and spectral intensity of laser-induced plasma on EAST-like plasma-facing materials in a vacuum

Real-time acquisition of the dynamic information on the surface elemental composition of the first wall, especially in the divertor region, is of great significance for understanding the plasma-wall interaction (PWI) process and optimizing the experimental conditions of the tokamak. The effect of laser ablation angles (LAAs) needs to be further evaluated for the in-situ laser-induced breakdown spectroscopy (LIBS) system on the EAST upper divertor that is being upgraded. LIBS experiments with a coaxial collection configuration were carried out at 1 × 10−5 mbar in the laboratory and over a wide range of LAAs from 0° to 72°. Tungsten (W), molybdenum (Mo), and copper (Cu) which are important plasma-facing materials in EAST were ablated under variable LAAs. Their ablation depth and ablation mass were measured by confocal microscopy. The depth ablation rate show that the larger the LAAs, the higher the depth resolution of LIBS, which is helpful for the depth-profiling analysis of the wall surface. The number of photons at the characteristic spectral line radiated from the three elements at a certain solid angle were obtained by using the absolute calibration method. The variation trend of the photon numbers with the increase of LAAs is consistent with ablation mass but slower than the downward trend of laser power density. By analyzing the variation of the spot size, the spatial intensity distribution of the laser, and the ablation crater morphology caused by the LAAs, it is found that the lateral ablation of the laser is the possible reason for the difference. Moreover, the calibration coefficient of spectral intensity under variable LAAs is obtained, which provides a reference for in-situ LIBS measurement.

Optical Logic Gate Operations With Single-Pixel Imaging

Optical computing has potential advantages of light-speed parallel processing and low power consumption over electronic computing. Logic gates are fundamental building blocks of modern computing systems. In this work, two types of single-pixel imaging systems are investigated for performing a non-imaging task of optical logic gate operations for the first time. In the first scheme, the spatial light intensity distribution of object image and illumination pattern is encoded based on the input binary values. Then the logic gate output result is indicated by the maximum single-pixel intensity when the encoded object image is incoherently illuminated by a most matched pattern. In the second scheme, the light amplitudes in corresponding sub-regions are directly proportional to the binary input values. A universal linear approximation model in the complex-amplitude domain allows the detected light intensity of a single-pixel holography system representing the logic gate output result. Various logic gate operations such as AND, OR and XOR can be implemented by these two systems in an individual or compound manner.

Regression of high-dimensional angular momentum states of light

The orbital angular momentum (OAM) of light is an infinite-dimensional degree of freedom of light with several applications in both classical and quantum optics. However, to fully take advantage of the potential of OAM states, reliable detection platforms to characterize generated states in experimental conditions are needed. Here, we present an approach to reconstruct input OAM states from measurements of the spatial intensity distributions they produce. To obviate issues arising from intrinsic symmetry of Laguerre-Gauss modes, we employ a pair of intensity profiles per state projecting it only on two distinct bases, showing how this allows to uniquely recover input states from the collected data. Our approach is based on a combined application of dimensionality reduction via principal component analysis, and linear regression, and thus has a low computational cost during both training and testing stages. We showcase our approach in a real photonic setup, generating up-to-four-dimensional OAM states through quantum walk dynamics. The high performance and versatility of the demonstrated approach make it an ideal tool to characterize high-dimensional states in quantum information protocols.

Impact of spatial distribution of light intensity on disinfection kinetics of Mycobacterium smegmatis and E. coli using TiO2-based photocatalyst

Impact of spatial distribution of light intensity on disinfection kinetics of Mycobacterium smegmatis and E. coli using TiO2-based photocatalyst

Selectively Exciting and Probing Radiative Plasmon Modes on Short Gold Nanorods by Scanning Tunneling Microscope-Induced Light Emission

We study the plasmon modes of gold nanorods (as short as ∼100 nm) on a nonmetallic conductive substrate using scanning tunneling microscope-induced light emission (STM-LE) with a nonplasmonic tungsten tip at room temperature in high vacuum (10–7 mbar). The far-field light is identified as the radiative decay of plasmon modes on the nanorods excited by inelastic electron tunneling. The spatial intensity distributions of the first three longitudinal multipolar modes on nanorods are spatially resolved on the order of 10–20 nm. These intensity distributions are related to the radiative electromagnetic local density of states and agree very well with numerical simulations. We discover that the presence of the tungsten tip with a high-dielectric constant influences the line shapes of the plasmon spectra and enhances the strength of the plasmon peaks.

3D single shot lensless incoherent optical imaging using coded phase aperture system with point response of scattered airy beams

Interferenceless coded aperture correlation holography (I-COACH) techniques have revolutionized the field of incoherent imaging, offering multidimensional imaging capabilities with a high temporal resolution in a simple optical configuration and at a low cost. The I-COACH method uses phase modulators (PMs) between the object and the image sensor, which encode the 3D location information of a point into a unique spatial intensity distribution. The system usually requires a one-time calibration procedure in which the point spread functions (PSFs) at different depths and/or wavelengths are recorded. When an object is recorded under identical conditions as the PSF, the multidimensional image of the object is reconstructed by processing the object intensity with the PSFs. In the previous versions of I-COACH, the PM mapped every object point to a scattered intensity distribution or random dot array pattern. The scattered intensity distribution results in a low SNR compared to a direct imaging system due to optical power dilution. Due to the limited focal depth, the dot pattern reduces the imaging resolution beyond the depth of focus if further multiplexing of phase masks is not performed. In this study, I-COACH has been realized using a PM that maps every object point into a sparse random array of Airy beams. Airy beams during propagation exhibit a relatively high focal depth with sharp intensity maxima that shift laterally following a curved path in 3D space. Therefore, sparse, randomly distributed diverse Airy beams exhibit random shifts with respect to one another during propagation, generating unique intensity distributions at different distances while retaining optical power concentrations in small areas on the detector. The phase-only mask displayed on the modulator was designed by random phase multiplexing of Airy beam generators. The simulation and experimental results obtained for the proposed method are significantly better in SNR than in the previous versions of I-COACH.

Simultaneous Manipulation of the Temporal and Spatial Behaviors of Nanosecond Laser Based on Hybrid Q-Switching

A hybrid Q-switching method based on a special-shaped saturated absorber was proposed for simultaneous manipulation of the temporal and spatial behaviors of a solid-state pulse laser. The temporal–spatial rate equation model of the laser was given and used to optimize the design parameter of the saturated absorber. Best spatial intensity homogenization performance can be expected using an active-passive hybrid Q-switched laser, comprising a Pockels cell and a cylinder Cr:YAG crystal with one end cut as a spherical concave surface. The optimized laser pulse width could be narrowed to 2.39 ns and the laser radial intensity distribution became quasi-super-Gaussian distribution with a radial intensity distribution ratio of 0.91, while that for the Gaussian beam was 0.84. In principle, the laser coherence can be maintained, and the laser spatial intensity distribution can be kept in a long propagation distance.

Spread of the Optical Power Emission of Three Units Each of Two Different Laser Therapy Devices Used in Sports Medicine, Which Cannot Be Assessed by the Users, Shown by Means of High-Fidelity Laser Measurement Technology

Laser therapy devices (LTDs) operating with near-infrared laser light are increasingly being used in sports medicine. For several reasons, users cannot evaluate whether or not such devices emit laser beams according to the specifications provided by the manufacturer and the settings of the device. In this study, the laser beams from two different LTDs that can be used in sports medicine were thoroughly characterized by measuring the emitted power, pulse shapes and lengths and spatial intensity distributions using professional, high-fidelity laser measurement technology. This was repeated for three units of each LDT independently to distinguish problems of individual units from potential intrinsic instrument design errors. The laser beams from the units of one LTD agreed with the settings of the device, with the measured average power for these units being within 3.3% of the set power. In contrast, the laser beams from the units of the other LTD showed large deviations between the settings and the actual emitted light. This device came with three laser diodes that could be used independently and simultaneously. The average power differed greatly between the units as well as between the laser diodes within each unit. Some laser diodes emitted essentially no light, which could lead to a lack of treatment for patients. Other laser diodes emitted much more power than set at the device (up to 230%), which could result in skin irritations or burning of patients. These findings indicate a need for better standardization and consistency of therapeutic laser light sources.

Frequency doubling of femtosecond laser pulses in three dimensional nonlinear photonic crystals

Quasi-phase matched nonlinear frequency conversion in three dimensional nonlinear photonic crystals (NPCs) has been considered for implementation of the second harmonic generation of transform-limited and chirped femtosecond laser pulses. Spatial distribution of the second harmonic intensity is shown to be caused by Cherenkov- and Raman–Nath-type nonlinear diffraction. These types of nonlinear diffraction may occur simultaneously resulting in an efficient multi-order nonlinear diffraction in the Bragg regime, which can be realized by a proper choice of the modulation period of NPC structure in longitudinal direction for considered transverse diffraction order. Three dimensional NPCs open up new possibilities for ultrafast nonlinear photonics and parametric interactions in optics.

Spatial Self-Phase Modulation in Graphene-Oxide Monolayer

The spatial self-phase modulation (SSPM) of the optical field revealed the magnitude and polarity of nonlinear refraction coefficients of the graphene-oxide (GO) atomic layers in an aqueous base solution with a resonant excitation using a chopped quasi-static laser at 532 nm. The SSPM of the optical field as a result of the intrinsic nonlinear refraction coefficient of GO atomic layers and the spatial distribution of intensity displayed the concentric diffraction rings at the far field due to the coherent superposition of transverse wave vectors. The number of concentric rings as a function of the applied intensity revealed the nonlinear refraction coefficient of GO which was estimated to be ~–6.65 × 10−12 m2/W for the laser-excitation duration of ~0.32 s, where the negative polarity of nonlinear refraction coefficient was confirmed with the interference image profile of SSPM. The upper and vertical distortion of concentric rings at the far field at the longer laser-excitation duration of ~0.8 s indicates the distortion of the coherent superposition of transverse wave vectors due to the localized thermal vortex of GO in the aqueous solution that offers novel platforms of thermal metrology based on localized optical nonlinearity and temperature-sensitive all-optical switching.

Dislocation characterization in c-plane GaN epitaxial layers on 6 inch Si wafer with a fast second-harmonic generation intensity mapping technique

Second harmonic generation (SHG) intensity, Raman scattering stress, photoluminescence and reflected interference pattern are used to determine the distributions of threading dislocations (TDs) and horizontal dislocations (HDs) in the c-plane GaN epitaxial layers on 6 inch Si wafer which is a structure of high electron mobility transistor (HEMT). The Raman scattering spectra show that the TD and HD result in the tensile stress and compressive stress in the GaN epitaxial layers, respectively. Besides, the SHG intensity is confirmed that to be proportional to the stress value of GaN epitaxial layers, which explains the spatial distribution of SHG intensity for the first time. It is noted that the dislocation-mediated SHG intensity mapping image of the GaN epitaxial layers on 6 inch Si wafer can be obtained within 2 h, which can be used in the optimization of high-performance GaN based HEMTs.

Focus in numbers: Characterizing protein oligomerization dynamics at DNA double strand breaks.

During radiotherapy, ionizing radiation (IR) is used to kill cancer cells by directly inducing high levels of genotoxic DNA double-strand breaks (DSB). These breaks are quickly detected and bound by DNA damage sensor proteins that activate a cascade of events leading to the recruitment and accumulation of repair factors (e.g. 53BP1) at sites of damage in dot-like structures called foci. The balance and interplay between the plethora of proteins recruited at the break site determine the choice of the repairing pathway, which can have paramount consequences on cell fate and ultimately in the response to cancer radiotherapy. Indeed, substantial evidence indicates that enhanced DSB repair (DSBR) capacity in individual patients is a major determinant in tumour radioresistance, while both radiosensitivity and the occurrence of radiotherapy-induced secondary cancers, are presumably associated with reduced DSBR function. Therefore, there is a pressing need to better understand the fundamental mechanisms of DSBR, towards improving the clinical management of patients undergoing radiotherapy. While it is clear that DNA repair relies on the balanced contribution of various repair factors, the oligomerization dynamics governing their organization into foci remain largely unknown. Here we combine Spatial Intensity Distribution Analysis (SpIDA) with an automated high-content foci detection algorithm to quantify the number of 53BP1 molecules at DSBR foci in cells challenged with increasing doses of the radiomimetic drug zeocin. Consistently with published data, 53BP1 foci number increases linearly at lower zeocin doses while plateauing at higher DNA damage load (zeocin concentration above 500 μg/mL). At this plateau, despite the availability of a nucleoplasmic protein pool, the number of 53BP1 molecules per focus decreases, suggesting a further not yet clarified layer of dynamic regulation potentially leverageable as therapeutical target.

Dynamics of shaded areas in a typical-shaped solar greenhouse and their effects on tomato growth—A case study in winter

The side walls and fixed insulation quilt of a solar greenhouse helped reduce heat loss from the room at night but produced shadows on the greenhouse floor during the day, affecting the growth and development of crops. In the present study, a method to calculate the projected area of the side walls and fixed insulation quilt in the greenhouse was derived. Then, a typical-shaped solar greenhouse and tomatoes were used as experimental research objects to investigate the spatial and temporal variation of indoor solar radiation intensity and tomato growth. The results showed that: 1) The average absolute error between the calculated and measured values of the ground shade of the solar greenhouse on four typical sunny days was 1.12%, 2.65%, and 2.02%, respectively. The area of selected greenhouse was 450m2, the maximum shaded area could account for 20.3% of the total area of the greenhouse, the shaded area projected by the insulation onto the greenhouse floor remained constant at different times, and that projected by the wall decreased and then increased parabolically with time. 2) The average solar radiation intensity in the greenhouse at the winter solstice tended to increase and then decrease with time, with a maximum value of 41,374.0 Lux. The uniformity of solar radiation distribution was reduced in the morning, evening and midday hours. 3) The tomato plant height, stem diameter, leaf area index and yield were 36.9%, 14.7%, 63.1% and 125.4% higher, respectively, in the high than in the low solar radiation zone. The results of the study can provide a theoretical basis for clarifying the dynamics of shaded areas and the spatial and temporal distribution of solar radiation intensity in greenhouses, and for optimizing the structural parameters of solar greenhouses.

Description and Evaluation of a New Deep Convective Cloud Model Considering In‐Cloud Inhomogeneity

AbstractConvections still need to be parameterized in general circulation models (GCMs) in the coming decades. Performances of GCMs are significantly influenced by the convection schemes used. In contrast to most conventional cloud models that ignore in‐cloud inhomogeneities, a new convective cloud model explicitly considering in‐cloud inhomogeneities is developed. The new model adopts a single bulk plume approach, but divides the plume into a series of interacting sub‐plumes in order to mimic the transition from the plume core to its edges. We implemented the new cloud model in NCAR Community Atmosphere Model version 5.0 (CAM5) and evaluated its performance. Single‐column tests show a stronger mass flux profile and low‐level detrainment with the new model. In global simulations, the long‐lasting wet bias in the tropical free troposphere of CAM5 is alleviated. Spatial pattern and intensity distribution of precipitation is improved, but the global hydrological cycle is over‐enhanced. The diurnal cycle of tropical precipitation is also better captured though the precipitation peak still occurs earlier than the observations and the amplitude of the cycle tends to weaken. MJO simulation is slightly improved with the new scheme. In addition, the new cloud model generated more tropical cyclones, in better agreement with observations.

Temporal and spatial evolutionary trends of regional extreme precipitation under different emission scenarios: Case study of the Jialing River Basin, China

Exploration of the temporal and spatial evolutionary trends of future extreme precipitation under different emission scenarios is of considerable importance for promoting active response to climate change. Based on the output of CMIP6 global climate models (GCMs) with four Shared Socioeconomic Pathways (SSPs), precipitation data for the Jialing River Basin (China) were obtained through CMhyd downscaling and correction. A relative threshold of 95 percentile of each year was used to extract extreme precipitation in the basin, and historical observational data were used to verify the capability of the GCMs to simulate extreme precipitation. Based on Extreme-point Symmetric Mode Decomposition, the trends and periodic characteristics of future extreme precipitation in the Jialing River Basin under four different emission scenarios (SSP2.6, SSP4.5, SSP7.0, and SSP8.5) were simulated and analyzed. The future temporal and spatial distributions of extreme precipitation frequency and intensity in different periods were described. The results revealed the following. (1) Future extreme precipitation in the Jialing River Basin is likely to increase with rates of 21.8 mm/10a, 11.4 mm/10a, 8.7 mm/10a, and 8.3 mm/10a for SSP8.5, SSP 7.0, SSP4.5, and SSP2.6, respectively. (2) The frequency of extreme precipitation decreased in the whole basin with a 1-day decrease of 3.88 % (SSP8.5), 7.11 % (SSP7.0), 5.66 % (SSP4.5), and 2.40 % (SSP2.6) from historical levels. (3) The intensity of extreme precipitation increased with a 1-day increase of 11.18 % (SSP8.5), 6.80 % (SSP7.0), 5.04 % (SSP4.5), and 4.57 % (SSP2.6) from historical levels. Over time, the change of extreme precipitation showed strong periodic characteristics with three periodic components of 2–3, 4–6, and 9–12 years. In terms of spatial distribution, the frequency (intensity) center of extreme precipitation in the next 80 years will be distributed in the south (southeast) of the basin. Compared with historical observations, the area of extreme precipitation intensity in the future accounted for a larger proportion, while the area of extreme precipitation frequency accounted for a smaller proportion. In terms of increased emission levels, the extreme precipitation frequency would decrease and the intensity would increase. The conclusions of this study could provide a reference for disaster prevention and mitigation of the effects of extreme precipitation under future climate change.

High extraction efficiency phosphor design applied in laser lighting.

Laser lighting has great potential to be the next generation of general lighting due to its high brightness and directionality. However, the light extraction efficiency and luminous efficiency from the light exit surface are greatly limited since phosphor structure. Here, we design and optimize a phosphor structure by Monte Carlo method (MCM) with optimization algorithm. The results indicate that the optimized Ce:YAG single crystal phosphor is able to improve the extraction efficiency to 0.49, which is much higher than the conventional parallel phosphor. The luminous efficiency of the optimized phosphor can also reach 230 lm/W. In addition, the experiments and simulations show that the extraction efficiency and luminous efficiency will reduce to 0.41 and 190 lm/W if there is scattering in the optimized phosphor. The spatial distribution of the light intensity and thermal stability of the optimized phosphor are also measured. The optimized phosphor is helpful to the design of side heat dissipation structure. In general, the optimized phosphor may play a significant role in the high-flux laser lighting and the method also provides a universal tool for the phosphor design.

Распространение спиновых волн в управляемом деформациями магнонном кристалле с пьезоэлектрическим слоем

The mechanisms of spin wave propagation in a magnonic-crystalline structure, which is a width-modulated magnetic microwaveguide loaded with a piezoelectric layer with a system of counter-pin electrodes, are considered. Computational modelling based on the finite element method has been used to estimate the transformation of the internal magnetic field in a magnonic crystal under the action of elastic deformations. The shift of the frequency band of the Bragg resonance and the depth of regression of the spin-wave signal at the frequency of the Bragg resonance when an electric potential is applied to the electrodes are observed. It is shown that changing the polarity of the electric field can effectively control the characteristics of the propagating spin waves and the spatial distribution of the dynamic magnetization intensity in the multiferroic structure.

Application of FY-4B Geostationary Meteorological Satellite in Grassland Fire Dynamic Monitoring

In this study, the channel data related to fire point identification of Advanced Geostationary Radiation Imager on Fengyun-4B (FY-4B/AGRI) and Advanced Meteorological Imager on GEO-KOMPSAT 2A (GK-2A/AMI) were cross-compared. A total of 267 sampling points in China (Guangdong, Guangxi, Guizhou, Yunnan, Hainan) were selected to carry out fine positioning correction on the data in different elevation intervals. Then, a fire monitoring algorithm based on FY-4B was proposed, in which the self-adaptive threshold adjustment of the underlying surface parameters and the reprocessing module of fire point identification were added. The algorithm can realize the high-precision and stable monitoring of fire. The continuous dynamic monitoring was carried out using the grassland fire Mongolia from April 18 to 20, 2022 as an example. The results showed that the parameters of FY-4B/AGRI and GK2A/AMI channels have high consistency. The root mean square error (RMSE) of reflection channel was 1.33%, and the maximum RMSE of brightness temperature channel was less than 1.3 Kelvin (K). Through the positioning analysis in different elevation intervals, the average longitude offset of FY-4B satellite data was -0.5°–0° and the average latitude offset was -0.9°–0.6°. Overall, these findings indicate that the high-frequency observations of FY-4B can be fully utilized to monitor forest and grassland fires, which can continuously track the dynamic evolution of fire and can distinguish the spatial distribution of different fire intensities in large-scale fire field.

К вопросу о механизмах разогрева светодиодов на основе p-InAsSbP/n-InAs(Sb)

Three main reasons for a temperature increase in activated p-InAsSbP/n-InAs/n-InAsSbP and p-InAsSbP/n-InAsSb/n-InAs double heterostructures has been considered. Contribution of nonradiative Auger recombination, electron-phonon interaction and Joule heating to diode temperature increase in single element LEDs and flip-chip diode arrays (1×3) were evaluated at forward and reverse bias using data on spatial distribution of the mid-IR radiation intensity and current-voltage characteristics.

On heating mechanisms in LEDs based on p-InAsSbP/n-InAs(Sb)

Three main reasons for a temperature increase in activated p-InAsSbP/n-InAs/n-InAsSbP and p-InAsSbP/ n-InAsSb/n-InAs double heterostructures has been considered, contribution of nonradiative Auger recombination, electron-phonon interaction and Joule heating to diode temperature increase in single element LEDs and flip-chip diode arrays (1x3) were evaluated at forward and reverse bias using data on spatial distribution of the mid-IR radiation intensity and current-voltage characteristics. Keywords: IR LED, IR diode array, Joule heating, Auger recombination, electron-phonon interaction.