Intensity Of Light Beam Research Articles

Nanostructure silver absorbance with polarized light spectroscopy (PLS) and mobile imaging

This study presents a novel interdisciplinary approach for characterizing the optical properties of nanostructured silver films, combining methodologies from polarized light spectroscopy (PLS) and mobile app-based spectroscopic image detection. Silver nanofilms were deposited using electron beam evaporation (EBE) and subsequently analyzed for their absorbance across the visible light spectrum through PLS spectroscopy. The innovative aspect of this study lies in the validation of PLS spectral data using a mobile application developed with MIT App Inventor, which analyzes the intensity of light beams captured in images taken by a smartphone. The findings indicate that the silver nanofilm exhibits peak absorbance at approximately 400 nm within the violet region, corroborated by the mobile app’s data, which shows the lowest light intensity. However, discrepancies were observed from 500 to 600 nm, likely due to ambient light interferences and inherent optical phenomena such as diffraction, reflection, and refraction. Despite these deviations, the app’s readings closely align with the PLS data, supporting the film’s selective absorption properties. This study demonstrates the potential of this multidisciplinary technique in nanomaterial research, highlighting the application of nanotechnology in material science and the transformative potential of integrating software engineering for in-depth material characterization. These findings open avenues for advancements in both academic and practical applications.

Programmable Assembly of Semiconductor Mesostructures Via Inorganic Phototropism

Plants exhibit a phototropic response and direct the addition of new biomass to optimize collection of solar insolation. Analogous inorganic phototropism growth enables the programmable assembly of complex 3D nanoarchitectures with instruction by an incoherent, unstructured, mW cm-2 intensity light beam. Inorganic phototropism has been demonstrated via the light-mediated electrochemical assembly of semiconductor deposits from solution-phase precursor ions. No structured light field (no photomask), no lithographic processes and no templating agents (ligands, surfactants, etc.) are utilized. Nevertheless, ordered nanoscale features are conformally assembled over full macroscale (cm2) areas with feature heights on the order of several um with growth times < 5 min. In-plane anisotropy is a function of the input polarization. Isotropic morphologies consisting of ordered arrays of nanoscale holes were generated using unpolarized illumination whereas linearly polarized light resulted in anisotropic lamellar structures with in-plane orientations set by the polarization direction. The structure pitch was dependent on the spectral distribution of the input light with shorter wavelengths effecting higher feature densities. The out-of-plane growth direction is related to the propagation direction of the input light. Time-varying optical inputs enable programming of 3D intricacy by evolving the in-plane structure along the out-of-plane dimension, e.g. an abrupt reduction in the input wavelength results in a concomitant increase in the interfacial density resulting in tuning fork structures. Additional morphological control has also been effected by using multiple simultaneous illumination inputs. Modeling of the growth using a combination of full-wave electromagnetic simulations of light absorption and scattering coupled with Monte Carlo simulations of mass addition successfully reproduced the experimentally observed morphologies and indicated that assembly was directed by evolution of the growth front to maximize anisotropic light collection. The assembly was observed to be a highly emergent phenomenon involving optical communication between neighboring features including cooperative scattering and synergistic absorption.

Engineered bacteria that self-assemble "bioglass" polysilicate coatings display enhanced light focusing.

Photonic devices are cutting-edge optical materials that produce narrow, intense beams of light, but their synthesis typically requires toxic, complex methodology. Here we employ a synthetic biology approach to produce environmentally-friendly, living microlenses with tunable structural properties. We engineered Escherichia coli bacteria to display the silica biomineralization enzyme silicatein from aquatic sea sponges. Our silicatein-expressing bacteria can self-assemble a shell of polysilicate "bioglass" around themselves. Remarkably, the polysilicate-encapsulated bacteria can focus light into intense nanojets that are nearly an order of magnitude brighter than unmodified bacteria. Polysilicate-encapsulated bacteria are metabolically active for up to four months, potentially allowing them to sense and respond to stimuli over time. Our data demonstrate that engineered bacterial particles have the potential to revolutionize the development of multiple optical and photonic technologies.

Formation of multibeam dynamic gradient interference light fields with refractive optical elements

This paper presents methods for the formation and properties of light fields that controllably vary in time and space, obtained as a result of the interference of three or four coherent light beams using refractive optical elements. The formation of three-beam and four-beam interference fields is carried out using trihedral and tetrahedral glass pyramids respectively. The possibility of the interference field displacement in the transverse plane is ensured by devices for controlled phase changes of at least two of the interfering beams. The directions of propagation of these beams do not lie in the same plane with the optical axis of the original beam incident on the pyramid. In threeand four-beam dynamic interference fields the peak intensity values are higher than in the original laser beams and two-beam interference fields, so it is advisable to use them for processing flat objects with laser radiation, moving the interference maxima along the surface of the object. With a pairwise azimuthal displacement of the propagation directions of four interfering beams around the longitudinal axis, a dynamic interference field is formed, the periodically structured maxima of which cyclically smoothly change their shape from cells to band and back. At different speeds of pairs of directions the interference structure of the maxima rotates around the longitudinal axis. Therefore, this field can be used for therapeutic effects on biological tissues and for mixing microparticles in suspensions and emulsions. Since the local maxima of the intensity of all these interference fields have dimensions of the order of several micrometers while exceeding in value the maximum intensity of the initial light beam, these fields in the cross section are gradient and therefore can be used not only for laser exposure, but also for moving ensembles of microparticles including for sorting and changing concentration.

Transient Non-Collinear Magnetic State for All-Optical Magnetization Switching.

Resonant absorption of a photon by bound electrons in a solid can promote an electron to another orbital state or transfer it to a neighboring atomic site. Such a transition in a magnetically ordered material could affect the magnetic order. While this process is an obvious road map for optical control of magnetization, experimental demonstration of such a process remains challenging. Exciting a significant fraction of magnetic ions requires a very intense incoming light beam, as orbital resonances are often weak compared to above-band-gap excitations. In the latter case, a sizeable reduction of the magnetization occurs as the absorbed energy increases the spin temperature, masking the non-thermal optical effects. Here, using ultrafast X-ray spectroscopy, this work is able to resolve changes in the magnetization state induced by resonant absorption of infrared photons in Co-doped yttrium iron garnet, with negligible thermal effects. This work finds that the optical excitation of the Co ions affects the two distinct magnetic Fe sublattices differently, resulting in a transient non-collinear magnetic state. The present results indicate that the all-optical magnetization switching (AOS) most likely occurs due to the creation of a transient, non-collinear magnetic state followed by coherent spin rotations of the Fe moments.

Investigation of nonlinear optical response and all-optical switching/modulation in pyrromethene 567 based on spatial self-phase modulation

Investigation on the response of pyrromethene 567 samples under the influence of a high-intensity 532 nm laser is carried out. When an intense light beam is absorbed by a medium, the phase of the beam undergoes a modulation, which in turn produces an interference pattern. Herein, we report the thermo-optic coefficient and nonlinear refractive index n 2 for low concentration of pyrromethene 567. All-optical switching/modulation using single and multiple wavelengths based on spatial self-phase modulation has been achieved. The work reveals the potential application of pyrromethene 567 in photonic devices including optical modulators, optical switches, and similar devices.

Estimation of Kerr angle based on weak measurement with two pointers.

In this paper, we propose a weak measurement method using two pointers to estimate the magneto-optical Kerr angle, which is robust to ellipticity. The double pointers are the amplified displacement shift and intensity of the post-selected light beam, which are the conventional information carried by the light beam and can be directly output by a detector (such as a charge-coupled device). We demonstrate that the product of the double pointers is only related to the phase variation between two basic vectors and independent of the amplitude errors. In the measurement process, when there is an amplitude change or additional amplitude noise between two eigenstates, the product of two pointers is very useful in extracting phase information and shielding amplitude noise. In addition, the product of two pointers has a good linear relationship with the phase variation and a larger dynamic measurement range. This method is applied to measure the magneto-optical Kerr angle of NiFe film. The Kerr angle can be directly obtained using the product of the light intensity and the amplified displacement shift. This scheme is of great significance for the measurement of the Kerr angle of magnetic films.

Encoding the Intensity and Phase Gradient of Light Beams with Arbitrary Shapes

We present an approach for engineering the intensity trajectory and phase gradient of light beams with arbitrary shapes by estimating their parametric equations using Freeman chain code and by applying the fast Fourier transform. The analysis of the electric field distribution expected for a given curve allows the phase extraction over each local coordinate, generating a phase pattern to be displayed over a spatial light modulator. The intensity and phase gradient of eight different shapes is encoded during our experiments. The far field intensity profiles are captured and compared in shape to those designed, while the encoded phase is demonstrated by implementing a common path interference setup with a pair of beams from the spatial light modulator. The designed beams, initially drawn either by hand or generated with software, exhibit both the intensity and phase profiles encoded onto them.

Non-linear X-ray Science

The advent of the laser in the early 1960s represented a revolution in Optics and Spectroscopy that is still impacting our lives to this day. The availability of coherent and intense beams of laser light enabled the birth of non-linear optics as first demonstrated by the historic experiments in 1961 on second harmonic generation, and the first observation of two-photon absorption. The rapid discovery of diverse non-linear (NL) optical methods had a deep impact in Science that were recognised by Physics (1981, 2018) and Chemistry (1999) Nobel Prizes.

OPTIMAL FOCUSING CONDITIONS FOR TWO-DIMENSIONAL GAUSSIAN LIGHT BEAMS WITH ARBITRARY INPUT POLARIZATION IN A PHOTOREFRACTIVE BARIUM-STRONTIUM NIOBATE CRYSTAL

Calculating nonlinear optical phenomena in a barium-strontium niobate photorefractive crystal we constructed a mathematical model of the two-dimensional linearly polarized Gaussian light beams propagation taking into account all components of the linear electrooptic tensor. We investigated the dependence of the light beam intensity on the polarization azimuth at the entrance of the crystal and on the direction of the external electric field applied to a photorefractive crystal. We determined the conditions under which the focusing of two-dimensional Gaussian light beams at the exit of the crystal is maximal.

Melanin effect on light beam intensity distribution in skin as a function of wavelength and depth from 200 to 1000 nm using Monte Carlo simulation

Light beam propagation inside biological tissue, is crucial for many fields. Giving that, we had investigated the effect of melanin, on light propagation inside different type of tissue. We had constructed phantoms that approximates a real tissue and mimic its reaction to light. The skin model of seven layers takes into consideration the volume fractions and optical properties of blood, water, and melanin content. We developed a Monte Carlo simulation to investigate the intensity distribution inside tissues of a light beam. The study is done for different Fitzpatrick skin types. We provide the intensity distribution and the penetration depth in the 200–1000 nm wavelength range.

Correlation Between Ion Contents in Acupuncture Points and Propagated Sensation Along Channels

Background: Propagated sensation along channels occurs because of stimulations during acupuncture therapies and tends to transmit the stimulating signals along the meridians. From the Western medicine aspect, researchers consider the phenomena as neurotransmissions initiated by nerves, and various ions regulate the physiological functions of the nervous systems. Objective: This research investigates the critical characteristics of ions at acupoints and the mechanism of propagated sensation along channels, crossing meridians in traditional Chinese medicine (TCM). Methods: This research first conducts experiments by applying intense pulse light beams, which replace the traditional acupuncture treatments, on designated acupoints of studied human subjects, and employs a thermal infrared imager to monitor the temperature responses, which are induced by post sensation, in adjacent regions of the acupoints. Meanwhile, the research applies a synchrotron radiation technique on adult SD (Sprague Dawley) rats. The study analyzes the output responses with an X-ray Absorption Fine Spectroscopy (XAFS) to investigate the ion distributions in the relevant acupoints, which trigger the propagated sensation crossing meridians. Results: Experimental results demonstrate significant temperature increases simultaneously at the stimulated acupoints and specific other acupoints, whether in the same meridians. Moreover, XAFS experimental results indicate significantly high calcium, potassium, and sulfide ions at the stimulated acupoint regions. On the contrary, the measured chloride ions level at the regions is correspondingly lower. Conclusions: The thermal infrared imager monitoring shows significant temperature variations of crossing-meridian acupoints after implementing the intense pulse light beams on designated acupoints, and it implies the occurring of prolonged sensation along channels using acupuncture therapies. The X-ray absorption spectrum demonstrates significant differences in ion amounts and distributions between the acupoints and non-acupoints, and acupuncture therapies result in ion concentrations in the correlated regions inducing propagated sensation crossing meridians in TCM. Hence, the stimulated acupoints operate as ion reservoirs to provide high-concentration of specific ions to trigger the crossing-meridian post sensation.

Photobleaching and Recovery Kinetics of a Palette of Carbon Nanodots Probed by In Situ Optical Spectroscopy.

Carbon dots (CDs) are a family of fluorescent nanoparticles displaying a wide range of interesting properties, which make them attractive for potential applications in different fields like bioimaging, photocatalysis, and many others. However, despite many years of dedicated studies, wide variations exist in the literature concerning the reported photostability of CDs, and even the photoluminescence mechanism is still unclear. Furthermore, an increasing number of recent studies have highlighted the photobleaching (PB) of CDs under intense UV or visible light beams. PB phenomena need to be fully addressed to optimize practical uses of CDs and can also provide information on the fundamental mechanism underlying their fluorescence. Moreover, the lack of systematic studies comparing several types of CDs displaying different fluorescence properties represents another gap in the literature. In this study, we explored the optical properties of a full palette of CDs displaying a range from blue to red emissions, synthesized using different routes and varying precursors. We investigated the photostability of different CDs by observing in situ their time-resolved fluorescence degradation or optical absorption changes under equivalent experimental conditions and laser irradiation. The results about different PB kinetics clearly indicate that even CDs showing comparable emission properties may exhibit radically different resistances to PB, suggesting systematic connections between the resistance to PB, the characteristic spectral range of emission, and CD quantum yields. To exploit the PB dynamics as a powerful tool to investigate CD photophysics, we also carried out dedicated experiments in a partial illumination geometry, allowing us to analyze the recovery of the fluorescence due to diffusion. Based on the experimental results, we conclude that the nature of the CD fluorescence cannot be solely ascribable to small optically active molecules free diffusing in solution, contributing to shed light on one of the most debated issues in the photophysics of CDs.

Cross-grating phase microscopy (CGM): In silico experiment (insilex) algorithm, noise and accuracy

Cross-grating phase microscopy (CGM) is a quantitative phase microscopy technique based on the association of a 2-dimensional diffraction grating (aka cross-grating) and a regular camera sensor, separated by a millimetric distance. This simple association enables the high-resolution imaging of the complex electric field amplitude of a light beam (intensity and phase) from a single image acquisition. While CGM has been used for metrology applications in cell biology and nanophotonics this last decade, there has been few studies on its basics, especially for the microscopy community. In this article, we provide a numerical algorithm that enables the in silico (i.e. computer-simulated) data acquisition, to easily vary and observe the effects of all the CGM experimental parameters using computer means. In the frame on this article, we illustrate the interest of this numerical algorithm by using it to explain and quantify the effects of several important CGM parameters (grating-camera distance, pixel size, light intensity, numerical apertures, etc.) on the noise, precision and trueness of CGM measurements. This work is aimed to push the limits of CGM toward advanced applications in biomicroscopy and nanophotonics.

Predicting sample heating induced by cantilevers illuminated by intense light beams

Hybrid microscopy based on Atomic Force Microscopy (AFM) and fluorescence microscopy represents a commonplace experimental approach to study cell biology processes in liquid media at physiological temperature. However, many types of experimental artifacts can arise depending on the fluorescence illumination and detection technique utilized. For example, fluorescence excitation light gets absorbed by AFM cantilevers inducing local heating provoking undesirable as well as uncontrollable cantilever deflections. Here we present a numerical modelling approach based on a Finite Element Model (FEM) to predict sample heating in liquid media quantitatively, depending on illumination wavelength, illumination pattern, and cantilever shape and composition. Modelling results indicate substantial local temperature increases in-line with temperature increases derived from experimental cantilever deflections induced by fluorescence excitation light. We predict temperature increases of ∼0.05 – 0.5 °C for wide-field illumination and ∼5 – 15 °C for confocal illumination within the boundary conditions established, which could, for example, induce local protein conformational changes. We conclude that sample heating is an important issue requiring consideration in experimental set-ups involving intense light illumination of AFM cantilevers, especially when conducting single molecule investigations.

Numerical investigations on a photonic nanojet coupled plasmonic system for photonic applications

A photonic nanojet (PNJ) from a microcavity is a narrow and intense beam of light used to enhance the emerging electric field. Metal nanoparticles (NPs), on the other hand, confine a strong field in their vicinity due to the resonance of the free electrons with the incident field. A hybrid combination of a microcavity with a NP can drastically enhance the output field. In this work, a systematic numerical study of the microcavity-NP system has been carried out to investigate the effect of the shape of the metal NPs on the output field strength. The single and their dimer NPs with different dimer nanogaps with PNJ producing microcavity have been investigated. Splitting of the broad dipole mode of the NP has also been observed. As an application of this study, the surface enhanced Raman spectroscopy factor of the order of 107 has been estimated for nano-cube dimer NP-microcavity hybrid system.

Structural changes of a radially symmetric thermocapillary flow in the shallow cavity partially covered by a solid film

This paper presents a numerical study of spatial transformations of a radially symmetric flow in a shallow fluid-filled cylindrical cavity partially covered by a solid non-deformable film. The upper central part of the liquid has a free surface where an intense light beam is focused to produce a hot spot on the symmetry axis. The heating generates a divergent thermocapillary motion on the free surface, which causes the fluid to flow under the immovable solid film. The edge of this film induces thermal perturbations, which, at specific heat generation values, begin to increase and give rise to a gradual radial flow symmetry breakdown that visually demonstrates the onset of vorticity in the azimuthal plane. Three-dimensional calculations have been carried out based on the interfacial hydrodynamics equations using Comsol Multiphysics software. The results of numerical calculations confirm that the instability occurs in the area corresponding to the boundary between the free surface and the solid film. The motion in the azimuthal direction becomes more evident with the growth of heating intensity. The vorticity in the azimuthal plane makes the flow structure significantly more complex compared to the axisymmetric radial flow. Thus, there is a predominantly radial flow in the area of free surface and, at the same time, the vortices with the azimuthal velocity component are observed under the film. As in the experiment, the number of vortices is determined by the ratio of the area of free surface to the covered area. It is shown that the appearance of motion in the azimuthal direction depends on the joint action of several physical mechanisms, which have been initialized in the theoretical model by means of various piecewise thermal and mechanical conditions at the upper boundary.

Method for stabilization of the microwave modulation index in order to suppress the light shift of the coherent population trapping resonances

For the resonance of coherent population trapping (CPT), we show that in the case of a spatially inhomogeneous light shift (for example, due to the Gaussian transversal profile of the light beam intensity), the zero position of the error signal, formed by the use of phase-jump technique, depends on the integration time of the spectroscopic signal. Basing on this effect, we propose two-loop method to stabilize the microwave power at the point where the light shift vanishes.

Simulation of quantum delayed-choice experiment through a single shot

A fundamental feature of micro objects is the wave-particle duality which is addressed by Bohr's complementarity principle. To observe the wave and particle behaviours, quantum delayed-choice experiments based on linear optics have been realized at the single-photon level. Since they were performed by using a single photon as the input, repeating measurements were required in order to obtain different experimental data and adjusting experimental parameters was necessary prior to each of measurements. Different from the previous works, we here realize a simulation of quantum delayed-choice experiment through a single shot, which employs a classical intense light beam as the input instead of a single photon. Experimentally, we demonstrate the trade-off between distinguishability and visibility of photons in a two-arm interferometer in an intuitive way by utilizing the finite beam profile of the light. We observe the morphing between wave and particle natures of photons via a single shot of a charged-coupled-device camera. Since the image is captured within the exposure time which is several milliseconds, the phase fluctuation is negligible, and therefore our experimental setup is robust against the noise. This work provides a simple and new route to inspect quantum duality, which does not require adjusting experimental parameters frequently and only needs performing measurement once.

Transmission of electromagnetic waves through nonlinear optical layers

The excitation of soliton states in optical layers exhibiting Kerr nonlinearities is theoretically investigated. The optical transmission coefficient is obtained as a function of the intensity of an incident light beam. The incident electromagnetic wave is considered to be monochromatic and linearly polarized in the transverse electric configuration. In materials exhibiting self-defocusing nonlinearity, soliton excitations are not observed if the product of the nonlinear dielectric coefficient of the slab and the absolute square of the incident electric-field amplitude is below a well-defined value. At such a limit, a soliton excitation with a position-independent electric field amplitude is observed within the nonlinear layer, regardless of the frequency value of the incident wave.