Pulsed Light Beam Research Articles

Wireless pulsed nanophotoelectrochemical cell for the ultrafast degradation of organic pollutants

An urgent demand exists for advanced-technologies to efficiently remove persistent organic pollutants from water, while minimizing energy consumption. Here, we introduce an innovative wireless nanophotoelectrochemical (nPEC) cell using pulsed light for the ultrafast degradation/mineralization of organic pollutants. The nPEC cell comprises a nanostructured Si-pn photodiode that monolithically integrates: (i) a Si-n/Au nanowire-based-photocathode for effective light absorption and photovoltage generation, and (ii) a Si-p/mesoporous-NiPt photoanode serving as catalyst to wirelessly amplify the sulfate radical production by low-intensity light without any bias voltage. The efficacy of the nPEC cell was shown by ultrafast degradation (>99 %) and mineralization (>98 %) of three emerging pollutants (tetracycline, levofloxacin and anatoxin-A). Notably, reaction kinetics were boosted by more than one order of magnitude when exposed to light intensities ca. 5-fold lower than sunlight. Remarkably, pulsed light beams in the 100–500 Hz range provided an additional enhancement in the degradation/mineralization efficiencies, reducing energy-input by half, while enhancing the catalyst's oxidation state and durability.

The Impact of a Pulsed Light Stream on the Quality and Durability of the Cold-Stored Longissimus Dorsal Muscle of Pigs.

The purpose of this study was to investigate the effect of pulsed light application (exposure to a pulsed light beam (PL) of 400 Hz for a period of 60 s, with an energy dose of 600 mW and wavelengths of 660 and 405 nm) on the physicochemical, technological, and sensory properties, as well as the nutritional value and shelf life of cold-storage pig longissimus dorsi muscle. Each muscle was divided into six parts, three of which were control samples, and the rest were exposed to pulsed light. The detailed laboratory tests of the meat were conducted 1, 7, and 10 days after slaughter. The meat was cold stored at +3 °C ± 0.5 °C. The study showed that the application of pulsed light has a favorable effect on lowering the TBARS index, oxidation-reduction potential, and water activity values. In addition, the application of PL had no statistically significant effect on the variation in the perception of selected sensory characteristics of meat. Furthermore, PL processing, as a low-energy-intensive method that can be environmentally friendly and thus have a large potential for implementation, is an innovative way to extend the shelf life, especially of raw meat, without a negative impact on its quality. This is of particular importance for food security (especially in the quantitative and qualitative aspects of food, but also in terms of food safety).

Self‐Referencing 3D Characterization of Ultrafast Optical‐Vortex Beams Using Tilted Interference TERMITES Technique

AbstractFemtosecond light pulses carrying optical angular momentums (OAMs), possessing intriguing properties of helical phase fronts and ultrafast temporal profiles, enable many applications in nonlinear optics, strong‐field physics, and laser micromachining. While generation of OAM‐carrying ultrafast pulses and their interactions with matters are intensively studied in experiments, 3D characterization of ultrafast OAM‐carrying light beams in spatiotemporal domain has, however, proved difficult to achieve. Conventional measurement schemes rely on the use of a reference pulsed light beam, which needs to be well characterized in its phase front and to have sufficient overlap and coherence with the beam under test, largely limiting practical applications of these schemes. Here a self‐referencing set‐up is demonstrated based on a tilted interferometer that can be used to measure complete spatiotemporal information of OAM‐carrying femtosecond pulses with different topological charges. Through scanning one interferometer arm, the spectral phase over the pulse spatial profile can be obtained using the tilted interference signal, and the temporal envelope of the light field at one particular position around its phase singularity can be retrieved simultaneously, enabling 3D beam reconstruction. This self‐referencing technique, capable of measuring spatiotemporal ultrafast optical‐vortex beams, may find many applications in fields of nonlinear optics and light–matter interactions.

Carbon functionalized bismuth vanadate thin films based photoelectrochemical logic gates

Carbon functionalized bismuth vanadate (BVO) photoanodes were synthesized using simple wet chemical process. To ascertain and determine various aspects of synthesized photoanodes, different types of characterization and measurements such as, X-ray Diffraction (XRD), Field emission scanning electron microscope (FE-SEM), UV–Visible (UV–Vis), Raman, Photoelectrochemical (PEC), Mott-Schottky (MS), and Electron Impedance Spectroscopy (EIS) have been carried out. Carbon functionalized BVO (C-BVO) photoanodes demonstrated superior photoconversion efficiency (η∼0.38%) and short circuit current (JSC∼0.50 mA/cm2 at 0.5 V vs. SCE) compared to pristine BVO. Bare BVO based PEC OR and AND logic gates have also been designed using pulsed white light beams. The PEC response reveals that for a white light beam with peak pump intensity of 100 mW/cm2, a photocurrent density of 83 μA/cm2 is generated at a bias of ∼0.5 V vs. SCE. Moreover, by tuning bias the photocurrent response can be inverted and further utilized to realize different logic operations simultaneously. The present study paves a new way for bismuth vanadate-based PEC computing devices.

Fractional GCEs behaviors merged: Prediction to the photoacoustic signal obtained with subdiffusive and superdiffusive operators

In this work, we developed a theoretical model with anomalous thermal diffusion by considering the modified Generalized Cattaneo Equations (GCEs) of Compte and Metzler, GCEI and GCEII, merged in a single operator by a linear combination in function of the fractional derivative order. This operator was compared with the generalization of Youssef for GCEIII. The range of the superdiffusive and subdiffusive regions was determined through phase velocity. In conclusion, both operators present unexpected sub- and superdiffusive intervals. Moreover, the temperature variation due to the heating by a pulsed light beam was determined. At the end, the photoacoustic signal for opaque samples was simulated varying the relaxation time and the fractional-order derivative.

ACCURACY OF MEASURING THE BOTTOM OF A POND BY AIRBORNE LIDAR BATHYMETRY (ALB)

Abstract. Airborne Lidar Bathymetry (ALB) is a technology for characterizing the depths of shallow-water bodies in relatively transparent waters from an airborne platform using a scanning and pulsed light beam. A bathymetric LiDAR usually uses wo laser pulses: one is a near-infrared (NIR) laser pulse for land topography and the other is a green laser pulse for submarine topography. In recent years, ALB has become more popular in river and coastal surveying in Japan. The accuracy of ALB has been verified by comparison with the results of acoustic sounding or levelling. However, since the comparison with either acoustic sounding or levelling is limited to a partial comparison at a point or on a line such as a cross section, it is not suitable for overall verification for detailed terrain features. In addition, accuracy verification by comparison between the results of ALB's green laser scanning and those of NIR laser scanning has been performed in the past only on land, but not in water. As scattering of the green laser occurs when measuring in water, it is possible to affirm that the verification under actual operating conditions has not been sufficiently investigated. In this study, we conducted NIR laser scanning in a natural pond and an artificial pool when they had no water, and conducted green laser scanning when they were filled with water. Thus, the NIR laser scanning and the green laser scanning could be compared in terms of surface measurement for the same bottom of the water body. It was confirmed that the green laser in water has sufficient accuracy compared to the NIR laser in actual operation conditions.

Refracting spacetime wave packets

A particular class of focused, pulsed light beams can propagate self-similarly in free space at a fixed group velocity. Now, scientists present a law of refraction that determines how the group velocity of these beams changes as they refract at an interface between two materials.

New Theoretical Model of the Irradiance Distribution in Water from a Unidirectional Point Source

Formulas are presented for calculating the irradiance field, which is formed in a turbid medium with a narrow scattering phase function and homogeneous optical properties when an infinitely narrow light beam passes through it. The calculations are based on a new mathematical model of the stationary radiation field of an omnidirectional point source and relationships enabling one to represent the irradiance distribution in a continuous or modulated light beam through this field. The obtained formulas, in contrast to the previously known ones, permit taking into account the temporal spreading of a pulsed light beam in the sea without a significant decrease in the accuracy of describing its spatial structure.

Transient polarized radiative transfer in cloud layers: numerical simulation of imaging lidar returns.

In this paper, we investigate the time-dependent backscattering halo of a pulsed light beam in a layer of scattering medium. We start from numerical simulations of polarized radiative transfer in the layer, which immediately reveals the effect under investigation. Then we analyze time-dependent structure of the light field using the simulation results. From the radiation field, we extract two principal components, immediately forming the halo structure. For each diffuse and ballistic component, we use the proper theoretical model, yielding a convenient analytic description of the time-dependent behavior of the radiation field. From the theory developed by us, we derive a simple numerical criterion of visibility of the halo. Finally, we validate our theory against Monte Carlo radiative transfer simulations. Thus, we propose a quantitative explanation of the studied effect.

Full-wave analysis of the scattering of a pulsed light beam by dielectric cylinders embedded in a homogeneous medium

An approach to study the time-domain scattering by a set of dielectric cylinders with circular cross section, placed in a semi-infinite medium, is presented. The illuminating light comes from a pulsed beam impinging onto the cylinders from outside the medium. The solution is developed in a semi-analytical way, starting from results based on the cylindrical wave approach pertinent to the case of illumination by a monochromatic plane wave. The method is numerically implemented to simulate the scattering response of buried cylinders illuminated by a pulsed Gaussian beam. In the presented results, the different contributions to the total scattered field are recognizable, giving an account of all the interactions between incident field, target and interface. The model adopted is well suited to the study, at optical frequencies, of scattering problems involving biological samples, such as vessels and fibers, embedded in tissues or immersed in fluids, through fast and accurate electromagnetic simulation.

Tighter focus for ultrashort pulse vector light beams: change of the relative contribution of different field components to the focal spot upon pulse shortening.

We investigate the focusing of Poisson-spectrum few cycle pulsed light beams for linear, circular, azimuthal, and radial input polarizations with and without a first-order vortex. It is shown that, for all the considered cases, the focal spot is tighter when compared to long pulses due to the increased blue frequency content in the ultrashort pulses spectrum. More significantly, we show, for what we believe is the first time, that upon pulse shortening different focused beam vector components associated with different Bessel functions J0 and J1 undergo a change in the relative weight of their respective contribution to the focal spot size. This effect is caused by the different spectral dependencies of J0 and J1 near the focus. This newly discovered property of broadband ultrashort pulses could be exploited in light-matter interactions advantageously.

Experimental investigation of the transient dynamics of slow light in ruby

When a pulsed light beam propagates through ruby, it is delayed by a slow-light mechanism. This mechanism has been the subject of debate (Wisniewski-Barker et al 2013 New J. Phys. 15 083020; Kozlov et al 2014 New J. Phys. 16 038001; Wisniewski-Barker et al 2014 New J. Phys. 16 038002). To distinguish between the two main proposed mechanisms, we investigate the trailing edge of a square-wave pulsed laser beam propagating through ruby. Our observation of a pronounced tail on the trailing edge of the transmitted pulse cannot be explained solely by the effects of a time-varying absorber acting upon the incident pulse. Therefore, our observation of the creation of a tail at the trailing edge of the pulse provides evidence for a complicated model of slow light in ruby that requires more than pulse reshaping. The different delays of individual Fourier components of the pulse signal explain the pulse distortion that occurs upon transmission through the ruby and must be accounted for by any model that attempts to describe the effects of slow light in ruby.

Efficiency and uniformity measurements of a light concentrator in combination with a SiPM array

A position sensitive Cherenkov detector was built, consisting of 64 SiPMs with an active area of 3×3mm2 and a pixel size of 100×100μm2. The sensitive area is increased by a light concentrator which consists of 64 pyramid-shaped funnels. These funnels have an entrance area of 7×7mm2 and an exit area of 3×3mm2, guaranteeing a sufficient position resolution e.g. for the barrel DIRC detector of the PANDA experiment at FAIR. The efficiency and uniformity of the light concentrator in combination with the SiPM array was tested by scanning the array in two dimensions, using a pulsed light beam. Results of these tests and comparison with simulations are given here.

Diffraction of broadband pulsed light beams

Intensity of broadband light pulses propagating in the free space has been calculated in the approximation of the narrowband signal envelope and based on the complex analytic signal. The approximation of the narrowband signal envelope is shown to be applicable for calculating the diffraction of pulsed light beams regardless of the duration and coherence of the pulse in space and time.

Correct Carrier Concentration for Lifetime Measurements with Local Illumination

Spatially resolved measurements of minority carrier lifetime are a valuable tool to monitor the quality of silicon wafers and of single processing steps. Common implementations of this technique generate excess minority carriers by scanning the variable focus of a pulsed light beam over the wafer surface. The resulting carrier distribution is spatially inhomogeneous; therefore minority carriers diffuse out of the illuminated area. However, most existing evaluation models neglect carrier diffusion, and hence overestimate the photogenerated minority carrier concentration by several orders of magnitude. This contribution presents a simulation model to calculate the correct local minority carrier concentration due to carrier diffusion for variable line and spot focus geometries. Carrier density distributions from spatially resolved photoluminescence measurements confirm the results of the model.

Thermal and acoustic effects in absorbing liquids under the action of pulsed light beams

We present the results from simulating the impact of pulsed light beams of different spatial structures (Gaussian, Bessel, singular) in absorbing liquids. Profiles of refractive index inhomogeneities excited in a medium are calculated and the kinetics of their relaxation is studied.

BER evaluation and waveform analysis of nonlinear opto-acoustic communication system

An opto-acoustic communication system with low bit-error-rate (BER) is achieved experimentally. High energy pulsed light beam (10mJ/pulse) is used to produce shock waves in water. We investigate the relationship between BER and peak to average ratio (P/A ratio) at different bit-rates and the BER curves are presented. The BER is superior to 1.0E−5 at the bit-rate of 200bit/s, while a simple pre-coding method is used. It is convinced that high speed and low BER air-to-underwater opto-acoustic communication can be realized.

The time-dependent energy-flux pattern in total reflection of a pulsed light beam

For total reflection of a pulsed light beam at the interface between vacuum and a negative permittivity medium, the electromagnetic fields and the associated energy-flux patterns in the two media are investigated analytically and numerically. For a TE (transverse electric) polarized pulsed beam with positive Goos–Hänchen shift, energy reflection occurs not only in the second medium but also in the first medium because of interference between the incident and reflected fields. However, for TM (transverse magnetic) polarization where the Goos–Hänchen shift is negative, reflection of energy flux occurs in the first medium (or in front of the interface). At the same time, the energy flux around the interface forms time-dependent loops which absorb energy from the incoming flux in the front edge of the pulse but release energy into the outgoing flux in the later edge of the pulse to ensure energy conservation. Therefore, the so-called causality paradox in TM polarization is caused by the fact that interference between incident and reflected fields in the first medium and energy-flux loops around the interface offer a shorter path for reflection of energy flux (or photons).

Total internal reflection of pulsed light beam upon ideal non-absorbing plasma

Total internal reflection (TIR) of a pulsed light beam from vacuum incident upon an ideal non-absorbing plasma was investigated theoretically using the Fourier transform method. Because of the Goos–Hänchen effect, the reflected pulsed beam undergoes distortions such as carrier frequency shift and chirp. The distortions are magnified on condition that the pulsed beam is TM-polarized and illuminates the interface at large angle of incidence, which should be avoided for reflection of pulsed beam upon optical mirrors with metal film. Meanwhile, it is shown that the Goos–Hänchen shift and time delay of this TIR can be both positive and negative, which is consistent with the results obtained from stationary phase theory.

Optoacoustic effects in absorbing liquids under the action of pulsed bessel light

The excitation of acoustic oscillations in absorbing liquids exposed to pulsed Bessel light beams has been considered theoretically. Spatial profiles of refractive index diffraction patterns and the kinetics of their excitation and relaxation have been studied based on a numerical solution of continuous medium motion equations in a Lagrangian form and a heat-transfer equation and using the Lorentz–Lorenz formula. The conditions for optimal excitation of spatially localized acoustic pulses have been determined.