Light Photons Research Articles

Optomagnonic frequency combs

Optical frequency combs are fundamentally important in precision measurement physics, bringing unprecedented capabilities of measurements for time keeping, metrology, and spectroscopy. In this work, we investigate theoretically the formation of a form of frequency combs in cavity optomagnonics, in which a ferrimagnetic insulator sphere supports optical whispering gallery modes for both light photons and magnons. Numerical simulations of the optomagnonic dynamics show that a robust frequency comb can be obtained at low power under the bichromatic pumping drive, and the comb spacing is adjustable. Furthermore, the optomagnonic frequency comb structure has abundant non-perturbative features, suggesting that the magnon-induced Brillouin light scattering process in cavity optomagnonics may also exhibit phenomena similar to those in atomic–molecular systems. In addition to providing insight into optomagnonic nonlinearity, optomagnonic frequency combs may also provide the feasibility of implementing frequency combs based on spintronic platforms and may find applications for precision metrology based on magnonic devices.

Nonlinear optical imaging by detection with optical parametric amplification (invited paper).

Nonlinear optical imaging is a versatile tool that has been proven to be exceptionally useful in various research fields. However, due to the use of photomultiplier tubes (PMTs), the wide application of nonlinear optical imaging is limited by the incapability of imaging under ambient light. In this paper, we propose and demonstrate a new optical imaging detection method based on optical parametric amplification (OPA). As a nonlinear optical process, OPA intrinsically rejects ambient light photons by coherence gating. Periodical poled lithium niobate (PPLN) crystals are used in this study as the media for OPA. Compared to bulk nonlinear optical crystals, PPLN crystals support the generation of OPA signal with lower pump power. Therefore, this characteristic of PPLN crystals is particularly beneficial when using high-repetition-rate lasers, which facilitate high-speed optical signal detection, such as in spectroscopy and imaging. A PPLN-based OPA system was built to amplify the emitted imaging signal from second harmonic generation (SHG) and coherent anti-Stokes Raman scattering (CARS) microscopy imaging, and the amplified optical signal was strong enough to be detected by a biased photodiode under ordinary room light conditions. With OPA detection, ambient-light-on SHG and CARS imaging becomes possible, and achieves a similar result as PMT detection under strictly dark environments. These results demonstrate that OPA can be used as a substitute for PMTs in nonlinear optical imaging to adapt it to various applications with complex lighting conditions.

Mathematical analysis of phototransduction reaction parameters in rods and cones

Retinal photoreceptor cells, rods and cones, convert photons of light into chemical and electrical signals as the first step of the visual transduction cascade. Although the chemical processes in the phototransduction system are very similar to each other in these photoreceptors, the light sensitivity and time resolution of the photoresponse in rods are functionally different than those in the photoresponses of cones. To systematically investigate how photoresponses are divergently regulated in rods and cones, we have developed a detailed mathematical model on the basis of the Hamer model. The current model successfully reconstructed light intensity-, ATP- and GTP-dependent changes in concentrations of phosphorylated visual pigments (VPs), activated transducins (Tr*s) and phosphodiesterases (PDEs) in rods and cones. In comparison to rods, the lower light sensitivity of cones was attributed not only to the lower affinity of activated VPs for Trs but also to the faster desensitization of the VPs. The assumption of an intermediate inactive state, MIIi, in the thermal decay of activated VPs was essential for inducing faster inactivation of VPs in rods, and possibly also in cones.

In‐situ Integrated Plasmonic TiN@ZIF‐67 Composites for the Photoreduction of CO2into Solar Fuels: Insights into their Plasmonic Interaction and Mechanism

AbstractPlasmonic materials (PMs) essentially equip the photocatalysts to harvest energy from visible light photons. Interestingly, these PMs also support the photocatalysts, which has been realized upon the advent of non‐noble metals‐based PMs. In this context, this study reveals an interesting feature of TiN@ZIF‐67 plasmonic composite photocatalysts towards CO2reduction under solar irradiation. The composite is prepared via anin‐situand direct integration process, where the plasmonic TiN nanoparticles are surface‐modified using 3‐aminopropyl‐triethoxysilane/H‐Imidazole‐2‐carbaldehyde in the former and polyvinylpyrrolidone in the latter process to construct the 1H2ImCHO‐TiN@ZIF‐67 and TiN/PVP@ZIF‐67 composites, respectively. The structural and functional properties in these composites are confirmed using XRD and FTIR spectroscopy techniques. It is observed from the TEM images that the in‐situ integration leads to deep‐surface attachments of TiN on ZIF‐67, which exerted a major impact in the CO2photoreduction. The 1H2ImCHO‐TiN@ZIF‐67 shows the simultaneous production of ∼0.11 and 0.15 mmol g−1 h−1of methanol and ethanol, respectively; whereas, the TiN/PVP@ZIF‐67 produces only ∼0.31 mmol g−1h−1of methanol. The obtained results demonstrate that developed in‐situ synthetic approach is promising for the synthesis of efficient plasmonic photocatalysts and the product formation during CO2photoreduction can be dependent on how PMs are integrated with the host photocatalysts.

Silicon nanowires obtained by metal-assisted chemical etching for photonic applications

The arising of new physical phenomena at the nanoscale promoted for the scientific community the emerging of silicon nanostructures for future challenging technologies involving innovative applications in light management and photonics. Silicon nanowires (Si NWs) are already considered strategic systems for very different applications such as microelectronics, energy, and sensors. Nonetheless, the use of Si NWs for photonic applications is very limited. The reason for these poor results in the photonic field is related to the fabrication methods that generally are used to obtain silicon nanowires. One of the most promising approaches to realize Si NWs with a low-cost and Si technology compatibility is metal-assisted chemical etching. In this paper, we report a review of silicon nanowires realized by metal chemical etching for photonic applications focusing our attention on the realization of light-emitting Si NWs.

Standard Method for the Determination of the Photocatalytic Activity of Titanium Dioxide TiO2 in a Black Body Reactor

Synthesis of semiconductors to be used as photocatalysis, solar fuels attracts a wide attention since semiconductors photocatalyst are the most effective techniques to harvest solar light for environmental remediation. To determine the activity of a semiconducting photocatalyst is by imploying a black body photoreactor,where is the reaction rate defined as the converted amount of a probe molecule per unit time (dn/dt).measuring the reaction rate of a probe compound with the same type of photoreactor to compare the activities of photocatalysts under identical irradiation conditions is a very general way. The black body like a reactor is a new practical application to measure the quantum yields of photochemical reactions (Φ) in liquid-solid heterogeneous systems. One of the most major advantage of this new method, it is too simple to determine the photocatalytic activity of a photocatalysts such as the TiO2 as long as the fraction of the reflected and transmitted light are negligible due to the reactor geometry and high optical density of the heterogeneous systems. The quantum yields of the hetrogeneous system is a direct reaction since there is a lack of reliable experimental methods which make the determination at any photocatalytic laboratories very easy. The quantum yields are defined as the number of molecules of a given reactant per photon of light absorbed by photocatalyst at a given wavelength.

A compact light shield for the Psyche gamma-ray spectrometer

A compact, low-mass light shield has been designed for the Psyche space mission high-purity germanium gamma-ray spectrometer. The spectrometer will be vented to space, which can allow solar photons to enter the cryostat and cause charge-induced noise. The light shield was designed to block more than 99.9% of solar photons while maintaining high molecular conductance to space vacuum. COMSOL simulations and experiments were performed to characterize light shield photon attenuation and molecular conductance. The light shield was integrated onto the gamma-ray spectrometer and photon suppression and vacuum performance were demonstrated.

Assessment of a low-cost commercial CCD for use in X-ray imaging

Charged coupled device (CCD) is an imaging sensor that can be used as a digital radiation position-sensitive detector in space applications, industrial and medical imaging, etc. Commonly, the CCDs used for X-ray imaging are expensive and needed more complicated control, electronic boards. In this work, a simple and low-cost commercial CCD model (TCD1304AP) has been used to implement X-ray imaging. Moreover, a CsI(Tl) scintillation crystal with different thicknesses of 2 and 5 mm has been utilized as an X-ray to light photon converter. The driving and data acquisition boards have been designed in straightforward implementation, which can be easily performed. Also, the appropriate integration times have been set to 10 ms and 420 ms for use in cases with and without scintillation crystals respectively. The results show that this sensor has an admissible response to X-ray imaging. There is about a below 8.3% relative difference between the actual and attained dimensions from images at the direct method. However, this difference increases up to 17.7% for the indirect method due to the optical propagation in the scintillator. Furthermore, the experiment for the determination of the PSF distribution indicates that the spatial resolution of this X-ray imaging is 2% in the direct method and 3% with a 2 mm CsI(Tl) scintillator.

Characterization of Multianode Photomultiplier Tubes for use in the CLAS12 RICH detector

We present results of the detailed study of several hundred Hamamatsu H12700 Multianode Photomultiplier Tubes (MaPMTs), characterizing their response to the Cherenkov light photons in the second Ring Imaging Cherenkov detector, a part of the CLAS12 upgrade at Jefferson Lab. The total number of pixels studied was 25536. The single photoelectron spectra were measured for each pixel at different high voltages and light intensities of the laser test setup. Using the same dedicated front-end electronics as in the first RICH detector, the setup allowed us to characterize each pixel’s properties such as gain, quantum efficiency, signal crosstalk between neighboring pixels, and determine the signal threshold values to optimize their efficiency to detect Cherenkov photons. A recently published state-of-the-art mathematical model, describing photon detector response functions measured in low light conditions, was extended to include the description of the crosstalk contributions to the spectra. The database of extracted parameters will be used for the final selection of the MaPMTs, their arrangement in the new RICH detector, and the optimization of the operational settings of the front-end electronics. The results show that the characteristics of the H12700 MaPMTs satisfy our requirements for the position-sensitive single photoelectron detectors.

Constraints on the extragalactic magnetic field strength from blazar spectra based on 145 months of Fermi-LAT observations

ABSTRACT Properties of the extragalactic magnetic field (EGMF) outside of clusters and filaments of the large-scale structure are essentially unknown. The EGMF could be probed with γ-ray observations of distant (redshift z > 0.1) blazars. TeV γ-rays from these sources are strongly absorbed on extragalactic background light photons; secondary electrons and positrons produce cascade γ-rays with the observable flux dependent on EGMF parameters. We put constraints on the EGMF strength using 145 months of Fermi-LAT observations of the blazars 1ES 1218+304, 1ES 1101−232, and 1ES 0347−121, and imaging atmospheric Cherenkov telescope observations of the same sources. We perform a series of full direct Monte Carlo simulations of intergalactic electromagnetic cascades with the elmag 3.01 code and construct a model of the observable spectra inside the point spread functions of the observing instruments for a range of EGMF strengths. We compare the observed spectra with the models for various values of the EGMF strength B and calculate the exclusion statistical significance for every value of B. We find that the values of the EGMF strength B ≤ 10−17 G are excluded at a high level of the statistical significance Z > 4σ for all the four options of the intrinsic spectral shape considered (power law, power law with exponential cutoff, log-parabola, and log-parabola with exponential cutoff). The value of B = 10−16 G is not excluded; it is still a viable option of the EGMF strength. These results were obtained for the case of steady sources.

Estimating the influence of various factors on the uncertainty of light collection simulation in scintillators

The paper is dedicated to the evaluation of statistical uncertainty of simulating the process of light transfer in NaI (Tl) and BGO scintillators by Monte Carlo method. The DETECT2000 program with a unified surface model was used. The process of light transfer (“fate”) by light photons was traced from the moment of appearance in the scintillator to the moment of passing through its exit window. The light collection coefficient was determined as the ratio of the number of photons that passed through the exit window to a given number of emitted photons. Different values of the number of emitted photons, optical transparency coefficients and fractions of the surface diffuse reflection were set. Multiple repetitions of the simulation process for a different set of properties made it possible to evaluate the precision and type A uncertainty of simulating the light collection coefficient for all possible options. It is shown that the uncertainty decreases when the statistics of the emitted photons is increased, and increases when the transparency and diffuse reflection fraction are decreased.

Cells in the mechanical spotlight

Brillouin microscopy, a technique that visualizes the transfer of energy from photons of light to phonons of mechanical energy (1), has emerged as a useful tool in the study of biological mechanics. Unlike other approaches to mechanical characterization, such as optical tweezers, atomic force microscopy (AFM), or rheology, Brillouin microscopy does not require physical contact between a probe and the specimen. Instead, the mechanical properties of the specimen are characterized by observing optical frequency shifts in the Brillouin scattered light from the specimen.

Classical Limits of Light Quanta

It is argued that from a formal point of view, the classical limit of light quanta or photons is not that of a point-like particle but that of a geometric ray. According to this view, standard particle-wave dualism, which is often used in schools to describe the quantum behavior of massive objects, could be replaced by a ray-wave dualism (or even a particle-ray-wave trialism), which seems to be more appropriate for massless quantum objects such as photons. We compare the limits leading from quantum electrodynamics to a classical (Hamiltonian) theory of particles for electrons with those leading from photons via Maxwell’s equations to geometric ray optics. We also discuss the question to which extent Maxwell’s theory for electromagnetic waves should be considered as being on the same formal level as Schrödinger’s or Dirac’s theory.

Towards compact phase-matched and waveguided nonlinear optics in atomically layered semiconductors

Nonlinear frequency conversion provides essential tools for light generation, photon entanglement, and manipulation. Transition metal dichalcogenides (TMDs) possess huge nonlinear susceptibilities and 3R-stacked TMD crystals further combine broken inversion symmetry and aligned layering, representing ideal candidates to boost the nonlinear optical gain with minimal footprint. Here, we report on the efficient frequency conversion of 3R-MoS2, revealing the evolution of its exceptional second-order nonlinear processes along the ordinary (in-plane) and extraordinary (out-of-plane) directions. By measuring second harmonic generation (SHG) of 3R-MoS2 with various thickness - from monolayer (~0.65 nm) to bulk (~1 {\mu}m) - we present the first measurement of the in-plane SHG coherence length (~530 nm) at 1520 nm and achieve record nonlinear optical enhancement from a van der Waals material, >10^4 stronger than a monolayer. It is found that 3R-MoS2 slabs exhibit similar conversion efficiencies of lithium niobate, but within propagation lengths >100-fold shorter at telecom wavelengths. Furthermore, along the extraordinary axis, we achieve broadly tunable SHG from 3R-MoS2 in a waveguide geometry, revealing the coherence length in such structure for the first time. We characterize the full refractive index spectrum and quantify both birefringence components in anisotropic 3R-MoS2 crystals with near-field nano-imaging. Empowered with these data we assess the intrinsic limits of the conversion efficiency and nonlinear optical processes in 3R-MoS2 attainable in waveguide geometries. Our analysis highlights the potential of 3R-stacked TMDs for integrated photonics, providing critical parameters for designing highly efficient on-chip nonlinear optical devices including periodically poled structures, resonators, compact optical parametric oscillators and amplifiers, and optical quantum circuits.

“Polyaniline nanoparticles: A study on its structural, optical, electrochemical properties along with some possible device applications”

In this report, the Polyaniline (PANi) nanoparticles (NPs) were synthesized by in-situ polymersation method. These PANi NPs were characterized by various standard techniques. The crystal structure study were done by Powder X-Ray diffraction (XRD) technique and confirms its amorphous structure. Scanning Electron Microscopy (SEM) images showed that this material shows micron size microfibers made up of NPs with less porosity. The Fourier Transform Infrared (FT-IR) spectroscopy confirms PANi NPs formation and dominant vibrations corresponding to its Quinone and benzene rings were very much visible in the data. From the UV-Visible spectroscopy data, the absorption data confirms the transitions related to its Quinone ring and pyran rings. The optical band gap was estimated to be around 2.47 eV and this material follows indirect allowed transition. From the Photoluminescence (PL) data, it showed various emission line in visible region after exciting it by various UV photons. PL data also confirms defects and bipolaron formation in it. The Cyclic Voltammetry (CV) of PANi was also studied and the parameters like specific capacitance (CP), energy density (ED),and power density (PD) were estimated. For the current material, the value of CP, ED, PD were calculated to be around 72F/g, 144 J/cm3, and 0.9 W/m3 respectively. Further the energy bands like highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of this material was determined by employing CV and the value obtained goes well as calculated by optical absorption techniques. The Electrochemical Impedance Spectroscopy (EIS) carried on PANi NPs (under different studied conditions) also reveals the formation of defects or the play of existing defects with the incident light photons. From practical application point of view, a diode like structure of this material was also fabricated. To this diode, current-voltage (I-V) and dielectrics spectroscopy measurements was carried out in dark and with photons of various wavelengths. Under different measured conditions, the I-V characteristics showed non-linear behavior. Under above experimental situations, the various parameters related with I-V characteristics were also calculated. Also this material show self-powered phenomenon, one of the essential conditions for photo detector/sensor applications. Further this device was also subjected to transient measurements. The reverse recovery time for this diode was calculated to be around 3.04 μs. The capacitance and loss studied on this device shows well dispersion with applied frequency. The observed capacitance and loss also show some changes in presence of different color of photons. The experimental data and overall properties shown by this material correlate with each other. The various properties shown by this material projects it a good candidate for future flexible optoelectronics applications.

Revisiting the evidences for spectral anomalies in distant blazars: New data on the photon-ALP mixing

ABSTRACT We re-examine possible dependencies on redshift of the spectral parameters of blazars observed at very-high energies (VHEs) with Imaging Atmospheric Cherenkov telescopes. This is relevant to assess potential effects with the source distance of the photon to axion-like particle mixing that would deeply affect the propagation of VHE photons across the Universe. We focus our spectral analysis on 38 BL Lac objects (32 high-peaked and 6 intermediate-peaked) up to redshift z ≃ 0.5, and a small sample of 5 Flat Spectrum Radio Quasars up to z = 1 treated independently to increase the redshift baseline. The 78 independent spectra of these sources are first of all carefully corrected for the gamma–gamma interaction with photons of the Extragalactic Background Light that are responsible for the major redshift-dependent opacity effect. Then, the corrected spectra are fitted with simple power laws to infer the intrinsic spectral indices Γem at VHE, to test the assumption that such spectral properties are set by the local rather than the global cosmological environment. We find some systematic anticorrelations with redshift of Γem that might indicate, although with low-significance, a spectral anomaly potentially requiring a revision of the photon propagation process. More conclusive tests with higher statistical significance will require the observational improvements offered by the forthcoming new generation of Cherenkov arrays (CTA, ASTRI, LHAASO).

Optical, luminescence, and energy transfer studies of Gd3+/Dy3+ doped potassium gadolinium borophosphate glasses

The K2O–Gd2O3–B2O3–P2O5 glass doped with Dy2O3 (Dy:KGPB) were synthesized by the melt-quenching technique. These glasses were subjected to characterize the physical, structure, optical and luminescence properties. It was observed that the density, molar volume and refractive index of glass increased with increasing Dy2O3 concentration. The FTIR result confirmed the main glass network of BOB and POP linkages those were degraded by adding Dy2O3 modifier. Glasses absorbed photons in ultraviolet, visible light and near-infrared region. The photoluminescence under direct Dy3+ excitation performed the strong emissions at 574 and 482 nm corresponding to 4F9/2 → 6H13/2 and 4F9/2 → 6H15/2 transition, respectively. The Gd3+ excitation also caused strong emission of Dy3+ by the Gd3+-Dy3+energy transfer. Glass doped with 1.00 mol% of Dy2O3 owned the highest emission intensity due to the concentration quenching. The lifetime of 4F9/2 level was found to decrease with addition of Dy2O3 content via dipole-diploe interaction between Dy3+ ion. Judd-Ofelt (J-O) intensity parameters were initially calculated and applied to evaluate the radiative parameters such as branching ratios, radiative transition probabilities, and stimulated emission cross-sections. The radioluminescence of glass was also investigated and found the scintillation efficiency around 15.6%, compared to BGO scintillator. The Dy:KGPB glass has an interesting potential for solid-state laser, LED and X-ray detection applications.

The dark side of the proton

We study the sensitivity of the High-Luminosity LHC to a light baryonic dark photon B, primarily coupled to quarks, as a constituent of the proton. This is achieved by allowing for a dark photon parton distribution function (PDF) in the PDF evolution equations. Depending on the mass and coupling of the dark photon, the evolution of standard quark and gluon PDFs is distorted to varying degrees. By analysing the effect of the dark photon on the tails of Drell-Yan invariant mass distributions, we demonstrate the potential of the LHC in determining competitive bounds on dark photon parameter space.

Comprehensive analysis of photon dynamics in thin-film GaAs solar cells with planar and textured rear mirrors

This study describes a comprehensive analysis of light trapping and photon recycling (PR) in thin-film GaAs solar cells, explicitly considering the effects of (non-perfect) light scattering at a textured rear mirror. We calculate the probabilities of escape, reabsorption in the absorber and parasitic absorption for internally generated photons, as well as the reflectance, absorptance and parasitic absorptance of externally incident photons. Combined with the internal luminescent efficiency to account for non-radiative recombination non-explicitly, but in a phenomenological manner, device performance metrics such as the short-circuit current density ( J s c ), open-circuit voltage ( V o c ) and its radiative limit, the external luminescent efficiency, the contribution of PR to the V o c and the power conversion efficiency ( P C E ) are derived. We analyze a typical thin-film GaAs solar cell architecture, consisting of an n-GaAs/p-InGaP heterojunction structure cladded by commonly employed front- and rear-side layer stacks. The probabilities of escape, reabsorption and parasitic absorption and the resulting performance metrics are presented as a function of absorber thickness, rear-mirror reflectivity, haze factor, internal luminescent efficiency, front grid coverage and band tailing. The simulations show that the implementation of a textured rear mirror reduces PR and its importance for device performance. In these textured cells, a high rear-mirror reflectivity and, thereby, efficient PR, is less crucial to achieve V o c values close to the radiative limit. The increased J s c in textured cells renders light trapping favorable for the P C E , regardless of absorber thickness and material quality and despite reduced PR. Furthermore, the impact of an absorbing front grid and lateral transport of internal luminescence on PR is estimated, emphasizing the importance of transparent (non-absorbing) contact layers, at the rear, but importantly, also at the front of the device. To conclude, P C E limits of 300-nm-thick GaAs solar cells are deduced in the context of an experimentally realized light-trapping scheme based on a randomly textured rear mirror. P C E s exceeding 25.5% are deemed realistic. • Photon recycling and light trapping are studied in textured thin-film GaAs cells • Ray-optical modeling yields probabilities of escape and (parasitic) absorption • Textured rear mirrors reduce photon recycling and its impact on cell performance • Light trapping improves efficiency for any absorber thickness and material quality • Efficiency limits of 300-nm GaAs cells are currently 25.5% and ultimately ¿28%

Spectral Lag Transition of 32 Fermi Gamma-Ray Bursts and Their Application on Constraining Lorentz Invariance Violation

The positive-to-negative transition of spectral lag is an uncommon feature reported in a small number of gamma-ray bursts (GRBs). An application of such a feature has been made to constrain the critical quantum gravity energy (E QG) of the light photons under the hypothesis that the Lorentz invariance might be violated. Motivated by previous case studies, this paper systematically examined the up-to-date GRB sample observed by Fermi Gamma-ray Burst Monitor for the lag transition feature to establish a comprehensive physical limit on the Lorentz invariance violation (LIV). This search resulted in 32 GRBs with redshift available, which exhibit the lag transition phenomenon. We first fit each of the lag–E relations of the 32 GRBs with an empirical smoothly broken power-law function, and found that the lag transition occurs typically at about 400 keV. We then implemented the LIV effect into the fit, which enabled us to constrain the lower limit of the linear and quadratic values of E QG, which are typically distributed at 1.5 × 1014 and 8 × 105 GeV, respectively.