Incident Light Intensity Research Articles

Thermo-optic hysteresis with bound states in the continuum

We consider thermo-optic hysteresis in a silicon structure supporting bound state in the continuum. Taking into account radiative heat transfer as a major cooling mechanism we constructed a non-linear model describing the optical response. It is shown that the thermo-optic hysteresis can be obtained with low intensities of incident light $I_0\approx 1~\rm{W/m^2}$ at the red edge of the visible under the critical coupling condition.

Sensitive and Efficient Fluorescent Fiber-Optic Sensor for In-Situ Hypoxia Detection in Solid Tumor

Accurate and timely assessment of malignant tumors in the early stage and therapy process is critical for making clear guidance and prognosis for the treatment, which can significantly elevate the cure rate of cancer patients. Fluorescent sensing and imaging of tumors have attracted extensive attention because of their advantages of high sensitivity and spatial resolution. A “plug-and-play” fluorescent fiber-optic sensor was reported for the diagnosis of tumor in our previous work. However, the route to obtain the optimization parameters and the spatial resolving capability of the tumor sensor were still elusive. In this work, we have systematically investigated the optimized design of the fiber from the aspects of structural morphology of the fiber tip, incident light intensity, and the concentration of the fluorescent probes that renders a limit-of-detection of 3 ng/mL and a response time less than 20 s. Furthermore, the sensor can reveal the hypoxic gradient of the solid tumor by virtue of its spatial sampling ability, enabling disease classification and margin identification potential. This proof-of-concept offers great opportunities for application in oncology, such as preoperative diagnosis, clinical operation guidance, and postoperative re-examination of tumors.

Design and Optimization of Liquid Crystal RIS-Based Visible Light Communication Receivers

In the design of reconfigurable intelligent surfaces (RISs)-aided visible light communication (VLC) systems, most studies have focused on the deployment of mirror arrays and metasurfaces on walls to influence signal propagation and enhance communication performance. This paper provides a new research direction in the design and performance optimization of RIS-aided VLC systems whereby voltage-controlled tunable liquid crystals (LCs) are deployed as part of the VLC receiver. The purpose of the LC RIS is to provide incident light steering and intensity amplification in order to improve the received signal strength and the corresponding achievable data rate. More specifically, an LC RIS-based VLC receiver design is proposed and its operating principles and the channel model for a VLC system with such a receiver are provided. Since the refractive index of the LC RIS plays a critical role in the wave-guiding and light amplification capabilities of this novel receiver, a rate maximization problem is considered to achieve the optimal refractive index and the required voltage to obtain the best light amplification and data rate performances. This communication design problem is a non-convex optimization problem for which a metaheuristic approach is developed based on the sine-cosine algorithm. Simulation results are used to confirm the considerable data rate improvement by the proposed LC RIS-based VLC receiver and optimization algorithm when compared to a VLC receiver without the LC RIS and a baseline scheme, respectively.

Filterless Visible‐Range Color Sensing and Wavelength‐Selective Photodetection Based on Barium/Nickel Codoped Bandgap‐Engineered Potassium Sodium Niobate Ferroelectric Ceramics

Photosensors, photodetectors, or color sensors are key components for various optical and optoelectronic applications. Semiconductor‐based photodetection has been a dominator which is excellent at measuring the photon intensity of incident light. However, the wavelength of the incident light to be measured must be known beforehand and it mostly depends on auxiliary methods to filter unknown wavelengths. Herein, an alternative but simple mechanism that is using a monolithic, bandgap‐engineered photoferroelectric ceramic to blindly determine the wavelength and intensity of incident light at the same time is demonstrated. The photoferroelectric compound is Ba‐ and Ni‐codoped (K,Na)NbO3 exhibiting a direct bandgap of ≈2 eV and a spontaneous polarization of ≈0.25 C m−2. The band–band charge carrier transition is confirmed by multiple characterization methods of photoluminescence, photodielectric spectroscopy, and photoconductivity. The existent optoelectrical cumulative effect enabled by the simultaneous narrow bandgap and strong ferroelectricity allows to reliably distinguish the wavelengths of 405, 552, and 660 nm as well as the power density ranging from ≈0.1 to 10 W cm−2, with the photoresponsivity of up to 60 μA W−1. Consequently, this work proposes an alternative to semiconductor‐based counterparts for filterless, wavelength‐selective photodetection and color sensing.

Fixing N2 into cyanophycin: continuous cultivation of Nostoc sp. PCC 7120

Two diazotrophic cyanobacteria (Anabaena cylindrica PCC 7122 and Nostoc sp. PCC 7120) were cultivated to produce cyanophycin, a nitrogen reserve compound, under nitrogen fixing conditions. In preliminary continuous experiments, Nostoc sp. was shown to be more efficient, accumulating a higher amount of cyanophycin and showing a greater capability to fix atmospheric nitrogen in the biomass (67 mgN d−1 of fixed nitrogen per liter of culture). The operating conditions were then optimized to maximize the cyanophycin productivity: the effect of incident light intensity, residence time and nitrogen availability were investigated. Nitrogen availability and/or pH played a major role with respect to biomass production, whereas phosphorus limitation was the main variable to maximize cyanophycin accumulation. In this way, it was possible to achieve a stable and continuous production of cyanophycin (CGP) under diazotrophic conditions, obtaining a maximum cyanophycin productivity of 15 mgCGP L−1 d−1.Key points• Diazotrophic cyanobacteria produce stable amount of cyanophycin in continuous PBR.• Nostoc sp. proved to be more efficient in producing cyanophycin than Anabaena sp.• P deprivation is the major variable to increase cyanophycin productivity in continuous.

Solar charging of a Zn-air battery

Solar-charging of Zn-air batteries has been studied by employing a photoelectrocatalytic or a photovoltaic system. Discharging of a Zn-air battery corresponds to oxidation of Zn and formation of ZnO. Charging is the reverse action, i.e., the reduction of ZnO and deposition of metallic Zn on the Zn electrode. In a typical Zn-air battery, charging also corresponds to water oxidation on the counter electrode and oxygen evolution. Because of the high overpotential for the oxygen evolution reaction, charging of the battery necessitates very high voltages, much higher than the voltage produced by the battery. This problem can be overcome by substituting oxygen evolution reaction by photocatalytic oxidation of an organic substance, which may be a biomass waste. This photoelectrocatalytic charging was presently realized with 100% Faradaic efficiency. More than 2 V of power gain was achieved through photoelectrocatalytic charging, i.e., a small input voltage was then necessary in order to charge the battery. Battery charging was also possible by using a photovoltaic cell as long as the cell provides enough open circuit voltage to overcome battery potential, overpotentials and losses. In the present case charging was possible with a commercial photovoltaic cell generating 2.25 V at an incident light intensity of 100 mW cm−2.

Using the design of dynamic experiments to optimize photosynthetic cyanophycin production by Synechocystis sp.

The production of cyanophycin by photosynthetic microorganisms, as a high-value bio-based compound, is getting increasing interest. The aim of this work is to maximize the production of this compound by the cyanobacterium Synechocystis sp. in semi-batch cultivation systems, by applying a data-driven modeling approach based on the Design of Dynamic Experiments (DoDE) and Response Surface Model (RSM) methodologies. A first set of experiments, carried out inside an initially defined domain, was used to find a preliminary RSM model describing cyanophycin concentration as a function of incident light intensity profile, temperature, and phosphorus supply profile. The model was then improved, according to an evolutionary optimization approach, by carrying out additional experiments in a modified domain, exploiting information derived by the initial model. The updated model was used to identify the optimal operating conditions resulting in maximum cyanophycin concentration at the end of the batch. The cyanophycin concentration found experimentally (228.2 ± 20.0 mg/L) in these conditions fell within the confidence interval of the model prediction. Remarkably, this experimentally obtained value represents a significant (about 20 %) increase in the cyanophycin production with respect to the highest value found in the experiments before the optimization step (184.3 ± 0.8 mg/L).

Investigation of structural and optical properties of graphene derivatives as a route for optical sensing

In the present research work, thick films of graphene oxide (GO) and reduced graphene oxide (rGO) were fabricated on glass substrate by using standard screen-printing technique. Silver paste was used to make contacts of thick films. Fabricated thick films of GO and rGO were characterized by scanning electron microscopy (SEM), elemental data analysis (EDS), and X-ray diffraction (XRD) to make sure the morphological, elemental and structural characteristics of the thick films. Optical characteristics of the fabricated thick films were carried out by UV Spectra, Raman spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR). In addition, the optical studies were performed by homemade system to investigate the effect incident light intensity with different colour (Blue, Yellow, and Green) filters on GO and rGO sensing. XRD and EDS confirms the materials were GO and rGO. The findings revealed that reduced graphene oxide has a high light absorption capacity to consider as an optical sensor.

Chlorella vulgaris cultivation under super high light intensity: An application of the flashing light effect

Chlorella vulgaris was grown under super high illumination (7000 μmolPhotonPAR/m2/s). Continuous and flashing light patterns were applied to investigate potential gain originating from the flashing light effect (square pattern, duty cycle of 0.5). Three control configurations were tested, all under continuous light: 200 μmolPhotonPAR/m2/s (conventional cultivation conditions), 4000 μmolPhotonPAR/m2/s (about the same average amount of energy), and 7000 μmolPhotonPAR/m2/s (maximum incident light intensity, cells did not grow). The experiments were conducted in ultra-thin flat-panel photobioreactors to ensure isoactinic growth conditions. After acclimation, the monitored outcomes were: growth rate, macronutrient composition (proteins, carbohydrates, lipids), pigment content, and transient fluorescence (OJIP assays). The results showed that Chlorella vulgaris can grow at a similar rate under 200 μmolPhotonPAR/m2/s of continuous light and under 7000 μmolPhotonPAR/m2/s of flashing light for frequencies between 0.1 and 100 Hz. Acclimation mechanisms did not alter cell macronutrient composition, yet, chlorophyll contents decreased while carotenoids increased (allegedly linked to an increased expression of the VAZ cycle). OJIP tests also revealed potential up-regulation of the water-water cycle (featuring PTOX enzyme), which would allow faster repletion of the PQ pool, delaying photosynthetic apparatus saturation. Above 100 Hz (1000 Hz in this study), cells exhibited the same growth rate as under the equivalent amount of continuous light. It suggests that light alternation is too fast for the cells to perceive it. On the contrary, too low frequencies (0.01 Hz) showed lower performances than under the same average intensity. In this condition, during the light phase, cells are exposed to harmful conditions (continuous 7000 μmolPhotonPAR/m2/s), and the too-long dark phase only allows the cells some rest but does not bring any benefits. In terms of applicability, these results pave the way for the use of super high light (either artificial or by sunlight concentration) to overcome the energy limitation burdening photoautotrophic microalgae cultivation.

Optical Fiber Multiparameter Detection and Numerical Simulation and Characteristics of Water Quality Particulate Matter Based on Single-Photon Detection Technology

Water quality testing is of great significance for daily water use or water use in high precision manufacturing. The use of single-photon detection technology to detect water particles is one of the important methods of physical water quality detection. However, the current water quality particle detection technology needs to be improved in the range and accuracy of turbidity detection. The paper aims to use single-photon detection technology to design a fiber optic turbidity detection system to solve the current problems of small turbidity detection range and low accuracy in a large range. In response to this, this paper has made an in-depth understanding of single-photon detection technology and designed two sets of detection schemes using the performance of photons. The first set is the transmission optical fiber turbidity detection, which can effectively detect the ultralow turbidity range and a wide range of water quality particles. The second set is a scattering optical fiber turbidity detection system, which can effectively detect water particles in the low and medium turbidity range. In this paper, the two systems were integrated into a whole system, so the results of the two detection methods can also be compared, and the detected turbidity can be obtained more accurately. The experimental results showed that for the transmission optical fiber turbidity detection system, the detection effect of the system was the best under the incident light intensity of 11 wm, and the fitting value was 0.99; for the scattering optical fiber turbidity detection system, the detection effect of the system was the best under the incident light intensity of 4 wm, and the fitting value was 0.99.

Facile self-assembly-based fabrication of a polyvinylidene fluoride nanofiber membrane with immobilized titanium dioxide nanoparticles for dye wastewater treatment

Photocatalytic membrane technology has received significant research attention because this system can continuously and safely purify wastewater without the post-process of separating and recovering the nanoscale photocatalysts. However, conventional membrane technology cannot wholly derive the photocatalytic performance due to the limitation in the loading contents of nanoscale photocatalyst and the reduced reactive sites. In this study, in order to overcome these issues and the limitations of current fabrication methods for photocatalytic membranes, a versatile and facile self-assembly approach for a polyvinylidene fluoride (PVDF) fiber-based reusable photocatalytic membrane with immobilized titanium dioxide (TiO2) nanoparticles is demonstrated to maximize the loading contents and photocatalytic reaction sites of nanoparticles on the surface of polymeric membrane. The TiO2 nanoparticles were successfully immobilized in high loading content on the surface of electrospun PVDF fibers using a poly(styrene-alt-maleic anhydride) as a self-assembly reaction agent at room temperature. Then, the physicochemical properties of the fabricated photocatalytic membrane and the manufacturing mechanism are systematically characterized. The photocatalytic properties of the membrane according to the loading of immobilized TiO2 nanoparticles are evaluated based on the degradation of various dye solutions under the illumination of a Xenon lamp (incident light intensity = 100 mW/cm2). The photocatalytic performance of the membrane is considerably enhanced when the loading of immobilized TiO2 nanoparticles on the PVDF fibers is higher as a result of a more vigorous self-assembly reaction. Furthermore, the reusability of the membrane is evaluated by repeating the dye removal process via adsorption and light irradiation; after the 20th cycle, it is demonstrated that the dye removal efficiency remains high without any leakage of TiO2 nanoparticles. The proposed facile fabrication method for a photocatalytic membrane with excellent reusability thus offers a new approach for the design of industrially applicable high-efficiency photocatalytic membranes.

Tunable Multi-Channels Bandpass InGaAsP Plasmonic Filter Using Coupled Arrow Shape Cavities

A new design for a tunable multi-channel plasmonic bandpass filter was numerically investigated using the two-dimensional finite element method (2D-FEM). The proposed multi-channel plasmonic bandpass filter consists of a metal-insulator-metal waveguide (MIM-WG) and double-sided arrow-shaped cavities. Silver (Ag) and a non-linear optical medium (InGaAsP) are used in the designed filter. InGaAsP fills the bus waveguide and arrow-shaped cavities. The refractive index of InGaAsP is sensitive to the incident light intensity, therefore the resonance wavelengths can be controlled. Utilizing different incident light intensities (such as 1017 v2/m2 and 2 × 1017 v2/m2) on the InGaAsP, the filter wavelengths can be tuned over a range from 600 nm to 1200 nm. The proposed filter with a confinement area of 0.5 μm2 can be used in wavelength division multiplexing (WDM), photonic systems, coloring filters, sensing, and 5G+ communication.

Investigation of Intensity Dependent Nonlinear Absorption in Cerium Phosphate Nanorods

Cerium Phosphate (CePO4) is a material that has attracted attention because of its unique properties, redox capabilities, and a wide variety of applications. Cerium Phosphate nanoparticles with a nanorod structure were successfully synthesized by a hydrothermal synthesis procedure using Cerium Nitrate Hexahydrate (Ce (NO3)3.6H2O) and Diammonium Hydrogen Phosphate ((NH4)2HPO4) as the precursors without adding any surfactants. The synthesized CePO4 nanorods were characterized using X-ray Powder Diffraction (XRD) and Transmission Electron Microscopy (TEM) analysis which showed pure monoclinic nanorod structures. The linear absorption was analyzed by UV-visible absorption spectrometry. The nonlinear absorption was measured by the open aperture Z-scan technique using a Q switched Nd-YAG laser at 532nm. The Z-scan curve exhibited reverse saturable absorption. In this study, the dependence of nonlinear absorption of CePO4 on the intensity of incident light was investigated. The non-linear absorption coefficient was measured and it was found that the non-linear absorption decreased with the increasing intensity.

Contact property depending on radiation intensity between the perovskite semiconductor layer and electrode film

Hybrid organic–inorganic perovskites have been widely studied in high-performance optoelectronic devices. Long-term stability is a key limitation to date in restricting their further development and commercial application. In general, interface properties between a semiconductor and an electrode highly affect device performance and stability. Herein, contact characteristics between the perovskite and electrode varying with illumination status have been first investigated. The results suggest that device's contact resistance (RC), obtained from a transfer length method, decreases as the incident light intensity increases. The RC under a higher irradiation intensity (1.26 mW/cm2) is about one-tenth of that at a lower density (0.08 mW/cm2). Simulation has been performed and shows a similar trend with experimental results. The interface physical model has been discussed based on an energy band theory. The band bending and barrier modulation at the interface under light illumination are originated from the surface states and the localized charges. This work explains the interface in determining device's fundamental properties, including stability, RC variation, and charge carrier transport process. It is significant in understanding the device working mechanism and providing a potential way for perovskite optoelectronic devices with enhanced stability and performance.

Shading Reduces Water Deficits in Strawberry (Fragaria X Ananassa) Plants during Vegetative Growth

ABSTRACT The strawberry (Fragaria × ananassa Duch.) is a commercially important crop with high water requirements, making strategies that mitigate the influence of water deficits on plant growth necessary. This study aimed to evaluate the effects of shading on the vegetative growth of strawberry cv. Sweet Ann under a water deficit. The treatments consisted of the combination of two levels of shading (light intensity reduced by 47% vs. non-shaded plants) and two levels of water availability (water deficit vs. well-watered plants). The water deficit reduced the leaf water potential from −1.52 to −2.21 MPa, and diminished stomatal conductance, net photosynthetic rate (from 9.13 to 2.5 µmol m−2 s−1), maximum quantum efficiency of PSII photochemistry (from 0.79 to 0.67), and biomass accumulation, but increased the electrolyte leakage. The shading allowed the water-deficient plants to maintain water potential (−1.58 MPa) and photosystem II efficiency (0.79) and to increase water use efficiency (from 14.80 to 86.90 µmol CO2/mmol H2O), net photosynthetic rate (from 2.40 to 9.40 µmol m−2 s−1) and biomass of leaves, crowns, and roots, as compared to the non-shaded plants without a water limitation. These results suggest, for the first time in strawberry, that a reduction in incident light intensity attenuates the effects of stomatic and non-stomatic limitations caused by a water deficit during vegetative growth in strawberry.

Model Based Optimal Control of the Photosynthetic Growth of Microalgae in a Batch Photobioreactor

The present paper investigates the optimal control of the photosynthetic growth process in an artificial light photobioreactor operated in batch mode, the objective being to find an optimal incident light intensity for which the consumption of light energy, for any amount of newly formed biomass, is minimal. By using a simple and reliable model for the photosynthetic growth of microalgae of microalgae, predictions can be made on the quantity of produced biomass and on the amount of light consumed, whose ratio gives the biomass yield on light energy. This variable is unimodal on the allowed range of incident light intensities and has been used as objective function. An improved objective function is proposed by using the specific growth rate and a weighing factor that allows obtaining the desired amount of biomass while the light energy consumption is optimal. A closed-loop control structure has been designed based on the developed optimization algorithm. The optimal controller has been validated in simulation, comparing different lengths of the optimization horizon and the sampling period. It was found that a bigger sampling period, for the cases where there is no online information on the biomass concentration, does not significantly affect the productivity. The optimization algorithm can be used either online or offline, being useful for various experimental setups.

Cultivation of the microalgae Chlamydomonas reinhardtii and Desmodesmus quadricauda in highly deuterated media: Balancing the light intensity.

The production of organic deuterated compounds in microalgal systems represents a cheaper and more versatile alternative to more complicated chemical synthesis. In the present study, we investigate the autotrophic growth of two microalgae, Chlamydomonas reinhardtii and Desmodesmus quadricauda, in medium containing high doses of deuterated water, D2O. The growth of such cultures was evaluated in the context of the intensity of incident light, since light is a critical factor in the management of autotrophic algal cultures. Deuteration increases the light sensitivity of both model organisms, resulting in increased levels of singlet oxygen and poorer photosynthetic performance. Our results also show a slowdown in growth and cell division processes with increasing D2O concentrations. At the same time, impaired cell division leads to cell enlargement and accumulation of highly deuterated compounds, especially energy-storing molecules. Thus, considering the specifics of highly deuterated cultures and using the growth conditions proposed in this study, it is possible to obtain highly deuterated algal biomass, which could be a valuable source of deuterated organic compounds.

Removal of Pollutants from Aqueous Solutions by using Zinc oxide Nanoparticles

>This work presents a low-cost method to produce Zinc oxide (ZnO) nanostructured materials for the treatment of water polluted with model organic pollutants (e.g., brilliant green dye). Zinc oxide was prepared using the thermal solvent technique at a temperature of 37°C, at pH 6, and the samples were incinerated for one hour at a temperature of (500°C). Also, silver doped ZnO (Ag-ZnO) was prepared by photo deposition using ultraviolet rays. The photodissociation of Brilliant green dye was studied using ultraviolet rays under different conditions in the presence of Ag-ZnO, studying the effect of some factors, such as the effect of dye concentration and intensity of incident light. The results showed that the smashing efficiency of the zinc oxide surface increased by 92.8% after adding silver. It also showed that the photocatalytic breakdown rate increases with decreasing concentration of Brilliant green dye. Increasing the intensity of the light led to an increase in the rate of photocatalytic breakdown.

Electrochemical impedance spectroscopy of WO3 photoanodes on different conductive substrates: The interfacial charge transport between semiconductor particles and Ti surface

Particulate film electrodes of n-type semiconductor oxides are promising for photoelectrochemical (PEC) water splitting. To improve the photoanodic performance, we investigated the effect of charge transport at the interface between the oxide particles and the conductive substrate using electrochemical impedance spectroscopy (EIS) under UV–visible light irradiation. As a model oxide, we prepared tungsten oxide (WO3) particle films on different conductive substrates of fluorine-doped tin oxide (FTO)-coated glass, indium tin oxide (ITO)-coated glass, and Ti plates at different calcination temperatures. The PEC properties of the WO3 electrodes were evaluated for water oxidation in 0.1 mol/L sulfuric acid. The photocurrent density of the WO3 films on Ti plate (Ti/WO3) monotonically increased as the calcination temperature increased up to 650 °C, whereas the WO3 films on FTO-coated and ITO-coated glasses were, as is well known, deactivated at such high temperatures. The EIS measurements of the Ti/WO3 photoanodes revealed that the series resistance (Rs) was low even after calcination at high temperatures. The charge-transfer resistance (Rct) of WO3 photoanodes estimated from EIS was dependent on the incident light intensity because the photocurrent density was proportional to the irradiance. We found that the Ti/WO3 photoanodes exhibited a resistance in addition to Rs and Rct. We assigned this resistance, which was not changed by the light intensity, to the interfacial charge transport resistance (Ri) between WO3 particles and the Ti substrate. A smaller Ri increased the photocurrent density of Ti/WO3 for the oxygen evolution reaction at higher applied potentials.

High-performance self-driven photodetectors based on self-polarized Bi0.9Eu0.1FeO3/Nb-doped SrTiO3 p-n heterojunctions

Ferroelectric (FE) materials, owing to their remarkable photovoltaic effects, are one class of the most promising materials candidates for self-powered photodetectors. Here, with the pronounced rectification ratio as large as 103 at electric bias of± 1.0 V and a low dark current of 12 pA, the self-polarized Bi0.9Eu0.1FeO3 (BEFO)/Nb-doped SrTiO3 (NSTO) p-n heterojunctions are synthesized. It is revealed that the BEFO/NSTO p-n heterojunctions achieve the excellent photovoltaic effect with a short-circuit current as high as 0.23 μA and an open-circuit voltage of 0.41 V under the light illumination of 405 nm in wavelength and intensity of 151.7 mW/cm2. More importantly, the built-in potential in the as-prepared heterojunctions offers the self-powered photo-detecting functionality, with the high light-on/off current ratio of 2.0 × 104, high responsivity of 0.64 mA/W and sensitive detectivity D* of 1.63 × 1010 Jones, and fast response speed of 50/44 ms without external bias voltage. In particular, the super-performance with R ~ 1.97 mA/W and D*~ 5.0 × 1010 Jones in the weak incident light intensity (1.4 mW/cm2) are demonstrated, better than most previously reported FE-based self-powered photodetectors. Moreover, the devices possess good ambient stability and reproducibility. This work provides a demo for optically driven high-performance electronic devices based on self-polarized ferroelectric materials.