Intense Laser Light Research Articles

Hot Carrier Photocurrent through MOS Structure

Flow of photocurrent through the metal-oxide-semiconductor structure induced by the pulsed infrared CO2 laser is investigated experimentally. In the case of a perfect insulator, the photocurrent has a photocapacitive character. Its rise is based on the hot carrier phenomenon; no carrier generation is present, only redistribution of laser-heated carriers takes place at the semiconductor surface. The magnitude of this displacement current is related to the capacitance of the structure and is dependent on the rate of the laser pulse change as well as on the laser light intensity. This effect can find application in the detection of fast infrared laser pulses as well as in the development of infrared photovaractors. Operation of such devices would not require cryogenic temperatures what is usually needed by the long-wavelength infrared semiconductor technique.

Macroscopic, layered onion shell like magnetic domain structure generated in YIG films using ultrashort, megagauss magnetic pulses

Study of the formation and evolution of large scale, ordered structures is an enduring theme in science. Generation, evolution and control of large sized magnetic domains are challenging tasks, given the complex nature of competing interactions in a magnetic system. Here, we demonstrate large scale non-coplanar ordering of spins, driven by picosecond, megagauss magnetic pulses derived from a high intensity, femtosecond laser. Our studies on a specially designed yttrium iron garnet (YIG) dielectric/metal film sandwich target, show the creation of complex, large, concentric, elliptical shaped magnetic domains which resemble the layered shell structure of an onion. The largest shell has a major axis over hundreds of micrometers, in stark contrast to sub micrometer scale polygonal, striped or bubble shaped magnetic domains in magnetic materials, or large dumbbell shaped domains produced in magnetic films irradiated with accelerator based relativistic electron beams. Micromagnetic simulations show that the giant magnetic field pulses create ultrafast terahertz (THz) spin waves and a snapshot of these fast-propagating spin waves is stored as the layered onion shell shaped domains in the YIG film. Typically, information transport via spin waves in magnonic devices occurs in the gigahertz regime, where devices are susceptible to thermal disturbances at room temperature. Our intense laser light pulse—YIG sandwich target combination, paves the way for room temperature table-top THz spin wave devices, operating just above or in the range of the thermal noise floor. This dissipation-less device offers ultrafast control of spin information over distances of few hundreds of microns.

Hirshfeld surface analysis, enrichment ratio, energy frameworks and third-order nonlinear optical studies of a hydrazone derivative for optical limiting applications

Organic materials with good third-order nonlinear optical (NLO) properties are used in optoelectronics for protecting human eyes and sensors from high intensity laser light. In this regard, herein we report the synthesis, structural analysis, and third-order NLO properties of an organic molecule N'-[(E)-(4-fluorophenyl)methylidene]biphenyl-4-carbohydrazide (FMBC) containing hydrazone moiety. The formation of the synthesized molecule is confirmed by identifying the functional groups through FTIR spectral analysis. The material possesses good thermal stability before the melting point of 242.5∘C and transparent in the entire visible region of the EM spectrum. The photoluminescence study revealed the blue light-emitting property of FMBC. The crystal structure is stabilized by N-H···O, C-H···O, and C-H···F hydrogen bond interactions. The interconnects in the crystal packing were envisioned quantitatively using Hirshfeld surfaces (HS) by 2D fingerprint plots. The main contribution to the HS comes mainly from C-H, H-H, and O-H interconnects which cover about 80 % of the total HS surface. The enrichment ratios show that the favorable contacts accountable for the crystal packing are C···H, N···H, O···H, and F···H. The breakdown of the interaction energies obtained for various molecular pairs shows the nature and strength of the interactions. The calculation of 3D energy frameworks suggests that contacts formed in the structure are largely due to the dispersion force followed by the electrostatic potential. Third-order NLO coefficients were extracted under the continuous wave (CW) regime using z -scan technique. The material is an excellent optical limiter with a threshold value of 3.42 kJ/cm2. [Display omitted]

Simple and efficient way to generate superbunching pseudothermal light

By modulating the intensity of laser light before rotating groundglass, the well-known pseudothermal light source can be modified into superbunching pseudothermal light source, in which the degree of second-order coherence of scattered light is larger than 2. With the modulated intensities following binary distribution, we experimentally observed the degree of second- and third-order coherence equaling 20.45 and 227.07, which is much larger than the value of thermal or pseudothermal light, 2 and 6, respectively. Numerical simulation predicts that the degree of second-order coherence can be further improved by tuning the parameters of binary distribution. It is also predicted that the quality of temporal ghost imaging can be improved with this type of superbunching pseudothermal light. This simple and efficient superbunching pseudothermal light source provides an interesting alternative to study the second- and higher-order interference of light in these scenarios where thermal or pseudothermal light source were employed.

An Image Quality Evaluation Model for Optical Strip Signal-to-Noise Ratio in the Target Area of High Temperature Forgings

Under the time-varying temperature, the high-temperature radiation of forgings and the change of reflection characteristics of oxide skin on the surface of forgings lead to the difficulty of obtaining images to truly reflect the geometric characteristics of forgings. It is urgent to study the clear and reliable acquisition method of hot forging feature image under time-varying temperature to meet the requirements of visual measurement of hot geometric parameters of forgings. Based on this, this chapter first puts forward the quality evaluation method of forging feature image, which provides guarantee for the accurate evaluation of feature image quality. Furthermore, the factors that affect the image quality, such as the radiation characteristics of forgings and the photographic characteristics of cameras, are analyzed, and the imaging spectrum which can effectively suppress the radiation intensity of forgings is determined. Finally, aiming at the problem that the quality of image acquisition is difficult to guarantee due to the drastic change of radiation intensity of forgings under time-varying temperature, an image acquisition method based on minimum signal-to-noise ratio (SNR) based laser light intensity adaptation is proposed, which significantly improves the definition of feature light strips in forging images at high temperature, and finally realizes the clear acquisition of feature images of large-scale hot forging under time-varying temperature.

Laser induced surface analysis of acoustic materials for noise reduction

Every material has its own surface configuration and the surface gets modified when it is treated using some surfactants. The action of surfactants on the material creates a number of elastic skeletal structures which enable the material to be used as acoustic material for absorption of sound. The sensitivity of the material to high intensity of sound has great importance in different technological applications. A laboratory designed noncontact laser based sensor has shown its credential by sensing the surface roughness, which is an essential and sufficient condition for measurement of the sound absorption coefficient. The sensitivity is measured from speckle contrast which provides the suitability of the material for sensing sound intensity. The estimation of surface roughness and the presence of porosity are well recognized by the speckle contrast which helps measure the efficiency of the sound absorption coefficient. The incident of a laser beam in the presence of sound intensity significantly enhances the sound absorption followed by the loss of kinetic energy due to high amplitude vibrations within the pores present on the surface of the material medium exposed under the high intensity of laser light.

Photopolymerized additive manufacturing materials: Modeling of the printing process, mechanical behavior, and sensitivity analysis

The physical–chemical processes involved in light-induced polymerization (photopolymerization) are widely exploited in additive manufacturing (AM) technologies such as Stereolithography and Digital Light Processing. The influence of the AM process parameters on the physical properties of manufactured components has been often investigated through empirical methods based on the trial and error approach, that is, by collecting and interpreting a large amount of experimental data. However, when desired physical properties are required, accurate modeling of the liquid–solid conversion is necessary. In this work, in order to determine the properties of the resulting material according to the adopted process setup, we present a multi-physics approach to model the physical–chemical transformation taking place in photopolymerization. The role played on the final mechanical properties by the laser light intensity and by its moving speed is considered. Further, the influence of the uncertainty of the process parameters is investigated through a sensitivity analysis. The proposed approach is suitable for investigating the reliability of additively manufactured components as well as for their design according to an optimum printing strategy. From the perspective of making innovative functional materials, the proposed multi-physics model allows tuning the printing process in order to get the desired distribution of mechanical properties.

A practical-use hydrogen gas leak detector using CARS

The purpose of this research is to develop a non-contact, fast response, practical-use hydrogen gas leak detector using Coherent Anti-Stokes Raman Spectroscopy (CARS). To make it realize, the optimization of its practical light source was investigated minutely for this detector. The light source condition to generate the highest Anti-Stokes Raman light is obvious on the theory, while it is not matched with its practical condition under the physical constraints. In this study, the light source configuration was devised in which the laser beam (355 nm) is split into two optical paths and the Raman cell filled hydrogen gas is arranged on the one side. As a result, it was found that when its irradiation ratio (R = Stokes light/Pump light) was 0.140 ≤ R ≤ 0.173, the generation efficiency of the anti-Stokes light was high. The high generation efficiency of anti-Stokes light can be maintained even if the laser light intensity and hydrogen pressure to the Raman cell are changed. We discussed the difference between the obtained experimental results and the theoretical results. The detection limit of hydrogen gas concentration of our detector was set to 500 ppm. As a result, hydrogen gas up to 200 ppm ± 15% (lower detection limit: 157 ppm) could be measured. In addition, the measurement value of the hydrogen gas leaking from a nozzle was considered under the acceptance situation, too.

Analysis of Curvature in Fiber Optic Cable for Macrobending-Based Slope Sensor

The analysis of fiber optics for macro bending-based slope sensors using SMF-28 single-mode optical fibers has been successfully conducted. Fiber optics were treated to silicon rubber molding and connected with laser light and power meters to measure the intensity of laser power generated. The working principle was carried out using the macrobending phenomenon on single-mode optical fibers. The intensity of laser light in fiber optic cables decreases in the event of indentation or bending of the fiber optic cable. Power losses resulting from the macrobending process can be seen in the result of the information sensitivity of fiber optics to the change of angle given. From the results of the study, the resulting fiber optic sensitivity value is -0.1534o/dBm. The larger the angle given, the lower the laser intensity received by the power meter.

Probing valley population imbalance in transition metal dichalcogenides via temperature-dependent second harmonic generation imaging

Degenerate minima in momentum space—valleys—provide an additional degree of freedom that can be used for information transport and storage. Notably, such minima naturally exist in the band structure of transition metal dichalcogenides (TMDs). When these atomically thin crystals interact with intense laser light, the second harmonic generated (SHG) field inherits special characteristics that reflect not only the broken inversion symmetry in real space but also the valley anisotropy in reciprocal space. The latter is present whenever there exists a valley population imbalance (VPI) between the two valleys and affects the polarization state of the detected SHG. In this work, it is shown that the temperature-induced change of the SHG intensity dependence on the excitation field polarization is a fingerprint of VPI in TMDs. In particular, pixel-by-pixel VPI mapping based on polarization-resolved raster-scanning imaging microscopy was performed inside a cryostat to generate the SHG contrast in the presence of VPI from every point of a TMD flake. The generated contrast is marked by rotation of the SHG intensity polar diagrams at low temperatures and is attributed to the VPI-induced SHG.

Stability and evolution of electromagnetic solitons in relativistic degenerate laser plasmas

The dynamical behaviours of electromagnetic (EM) solitons formed due to nonlinear interaction of linearly polarized intense laser light and relativistic degenerate plasmas are studied. In the slow-motion approximation of relativistic dynamics, the evolution of weakly nonlinear EM envelope is described by the generalized nonlinear Schrödinger (GNLS) equation with local and nonlocal nonlinearities. Using the Vakhitov–Kolokolov criterion, the stability of an EM soliton solution of the GNLS equation is studied. Different stable and unstable regions are demonstrated with the effects of soliton velocity, soliton eigenfrequency, as well as the degeneracy parameter $R=p_{Fe}/m_ec$ , where $p_{Fe}$ is the Fermi momentum and $m_e$ the electron mass and $c$ is the speed of light in vacuum. It is found that the stability region shifts to an unstable one and is significantly reduced as one enters from the regimes of weakly relativistic $(R\ll 1)$ to ultrarelativistic $(R\gg 1)$ degeneracy of electrons. The analytically predicted results are in good agreement with the simulation results of the GNLS equation. It is shown that the standing EM soliton solutions are stable. However, the moving solitons can be stable or unstable depending on the values of soliton velocity, the eigenfrequency or the degeneracy parameter. The latter with strong degeneracy $(R>1)$ can eventually lead to soliton collapse.

The influence of laser beam and high light intensity on lentil (Lens culinaris) and wheat (Triticum aestivum) seedlings growth and metabolism

Light is considered as an environmental signal that controls plants growth and development. Sufficient duration, quality and wavelength are mainly responsible for switching on/off many physiological processes. The aim of this study was to examine the role of gamma aminobutyric acid (GABA) shunt pathway specific response in wheat (Triticum aestivum) and lentil (Lens culinaris) seedlings to blue LED laser (intensity= 1.48 W/cm2) and high intensity invisible ultraviolet light (intensity= 3.99 W/cm2) treatments separately, with respect to: seed germination, seedling growth, oxidative damage in term of reactive oxygen substances accumulation, GABA accumulation level, total proteins and total carbohydrates level and glutamate decarboxylase gene (GAD) expression. Data showed a remarkable changes in proteins content, carbohydrates content, chlorophyll level, dry and fresh weight, GABA accumulation, MDA level, and GAD m-RNA level under blue LED laser and high intensity invisible ultraviolet light treatments; separately in the both wheat and lentil cultivars. There were no significant differences of root emergence in all cultivars under all treatments. The concentrations of MDA increased in all cultivars under blue LED laser and high intensity invisible ultraviolet light treatments with increasing exposure durations. GABA levels increased and correlated significantly in all cultivars as the exposure duration of blue LED laser and high light intensity increased. Significant decrease in chlorophyll a and b contents in Um Qayes, Jordan1 and Jordan2 cultivars under all laser and high intensity invisible ultraviolet light treatments. A significant difference was found in proteins content in all cultivars in response to laser and high intensity invisible ultraviolet light treatments. Carbohydrates content in all cultivars used in this study were significantly decreased under laser treatments. The transcription level of GAD increased significantly under blue LED laser and high intensity invisible ultraviolet light in all cultivars used in this study. GAD expression was high in Hurani75 cultivar in agreement with the low level of GABA accumulation under high intensity invisible ultraviolet light at 60 min which strongly suggested that GABA was catabolized to enter another pathways (C:N balance) that was confirmed by increase in higher level of carbohydrates and proteins beside reduction in MDA content at the same exposure duration. On other hand, GAD expression in Jordan 2 was lower in response to laser treatment under the same exposure duration. The high increase of GAD gene expression explains the high accumulation of GABA level under both treatments. Results indicated that GABA shunt is a key metabolic pathway that allows wheat and lentil to adapt blue LED laser and high intensity invisible ultraviolet light stressful treatments.

Experimental studies on static laser light scattering of synthetized poly (acrylonitrile-co- methyl methacrylate) copolymer at room temperature

The static light scattering technique (SLS) is one of the absolute techniques that are used for the determination of weight average molecular weight (M¯w) of polymer solutions. In this technique, the scattered laser light intensity is measured at different scattering angles for various polymer concentrations to construct the Zimm plot which can be used for a simultaneous determination of M¯w, radius of gyration (Rg), and the second virial coefficient (A2). In this study, Poly (acrylonitrile–co-methyl methacrylate) copolymer, P(AN-co-MAA), was synthesized from acrylonitrile (AN) and methyl methacrylate (MMA) monomers using the precipitation polymerization method. Polymerization was carried out using potassium persulfate (K2S2O8) as an initiator with monomer ratios 1:1 of AN: MMA. The co-polymerization process was verified by Fourier transform infrared spectroscopy (FTIR). Refractive index (n) and refractive index increment (dn/dc) of the P(AN-co-MAA) copolymer solutions were determined experimentally using a Mach-Zehnder interferometer excited by a low power He-Ne laser in order to calculate the M¯w, Rg, and A2 of the synthetized copolymer using the static laser light scattering technique. M¯w, Rg, and A2 were found to be 9.7 × 105 g/mol, 345 nm, and 5 × 10−7 mol. cm3/g2.

The Effect of Laser Re-Solidification on Microstructure and Photo-Electrochemical Properties of Fe-Decorated TiO2 Nanotubes.

Fossil fuels became increasingly unpleasant energy source due to their negative impact on the environment; thus, attractiveness of renewable, and especially solar energy, is growing worldwide. Among others, the research is focused on smart combination of simple compounds towards formation of the photoactive materials. Following that, our work concerns the optimized manipulation of laser light coupled with the iron sputtering to transform titania that is mostly UV-active, as well as exhibiting poor oxygen evolution reaction to the material responding to solar light, and that can be further used in water splitting process. The preparation route of the material was based on anodization providing well organized system of nanotubes, while magnetron sputtering ensures formation of thin iron films. The last step covering pulsed laser treatment of 355 nm wavelength significantly changes the material morphology and structure, inducing partial melting and formation of oxygen vacancies in the elementary cell. Depending on the applied fluence, anatase, rutile, and hematite phases were recognized in the final product. The formation of a re-solidified layer on the surface of the nanotubes, in which thickness depends on the laser fluence, was shown by microstructure studies. Although a drastic decrement of light absorption was recorded especially in UV range, laser-annealed samples have shown activity under visible light even 20 times higher than bare titania. Electrochemical analysis has shown that the improvement of photoresponse originates mainly from over an order of magnitude higher charge carrier density as revealed by Mott-Schottky analysis. The results show that intense laser light can modulate the semiconductor properties significantly and can be considered as a promising tool towards activation of initially inactive material for the visible light harvesting.

Tuning the Δn and scattering in Bayfol® HX based holograms

Self-developing photopolymers are crucial materials for making high efficiency volume holograms. A key feature is the tuning of the refractive index modulation (Δn), but at the same time, it is crucial to minimize the light scattering which reduces the efficiency and increase the unwanted light. Here, we study Bayfol® HX materials in terms of scattering formation and control of the Δn by means the realization of Volume Phase Holographic Gratings (VPHGs), which are intended for the application in spectroscopic instrumentation. We highlight the dependency of the Δn and scattering with the laser light intensity, showing that the increase of the intensity reduces the amount of scattering. In addition, the fine tuning of the Δn with the incoherent light pre- and co-exposure is studied and the full dynamic range can be addressed controlling the scattering. A modified diffusion model is also used to describe and predict the experimental results.

Generation of a quasi-static magnetic field by a circularly polarised laser pulse due to tunnelling gas ionisation

We present a theoretical model of the quasi-static magnetic field generation in a laser channel, which is formed behind the front of a short laser pulse that ionises a gas. The generation of a magnetic field is caused by the appearance of the electron pressure anisotropy during tunnelling ionisation of atoms. In the considered case of subrelativistic laser light intensities, the generated magnetic field can reach ∼1 MG with an energy transformation ratio of about 1 %, which paves the way for identifying the proposed mechanism when use is made of a wide class of ultrashort pulse lasers.

Curvature Analysis in Fiber Optic Cables as a Tilt Sensor Based on Macro Bending

The test has been successfully carried out on optical fibers to be used as a macrobending tilt sensor using SMF-28 single mode optical fiber. The optical fiber was molded with silicon rubber, then connected to a laser light and a power meter to see the intensity of the laser power produced. The principle is carried out using the macro bending phenomenon on single mode optical fibers, where the laser light intensity in the fiber optic cable will decrease if there is a bend or bending in the fiber optic cable. We can observe the power loss resulting from the macro bending process to find out how sensitive the optical fiber is to changes in a given angle. The resulting optical fiber sensitivity value is -0.1534o/dBm.

Attosecond electron bunch measurement with coherent nonlinear Thomson scattering

We present a novel method for measurement of ultrashort electron-bunch duration, in principle, as short as zeptosecond (${10}^{\ensuremath{-}21}\text{ }\text{ }\mathrm{s}$). The method employs nonlinear Thomson scattering of relativistically intense laser light, and takes advantage of the nonlinear dependence and coherence of scattered light on electron bunch length. We validate the method and test its range of applicability via simulations by using realistic (nonideal) electron beams. Due to the wide flexibility in choice of interaction geometry and scattering laser pulse properties enabled by the method, it is shown to be applicable over a wide range of electron beam parameters, including energy, energy spread, and divergence angle.

Nonlinear Scattering of Near-Infrared Light for Imaging Plasmonic Nanoparticles in Deep Tissue

Nonlinear optical microscopy can obtain three-dimensionally resolved images within a specimen by exploiting the nonlinear light–matter interaction between the excitation light and sample. However, the image contrast significantly degrades with increasing observation depth because the emitted signal attenuates during light propagation through layers of the tissue before being detected. To obtain high contrast images from deep tissue, we developed saturated excitation (SAX) microscopy using the nonlinearity of near-infrared (NIR) plasmonic scattering from gold nanoshells and gold nanorods. SAX microscopy selectively detects the nonlinear component from the scattering signal generated by nanoparticle probes located at the center of the focal spot. By using this technique, background signals generated at out-of-focal positions are effectively removed. In addition, emitted signals in the NIR from nanoparticle probes efficiently transmit through biological tissue and are ideally suited to image deep parts of the tissue. We experimentally confirmed that scattering intensities from a single gold nanoshell and gold nanorod exhibit nonlinear relations with the excitation intensity of CW laser light at 780 and 1064 nm, respectively. We also demonstrated improvements of image contrast and spatial resolution at the depth of 400 μm in a phantom of muscle tissue by selectively detecting the nonlinear scattering signal component from gold nanoshells.

Self-Blinking Dyes Unlock High-Order and Multiplane Super-Resolution Optical Fluctuation Imaging.

Most diffraction-unlimited super-resolution imaging critically depends on the switching of fluorophores between at least two states, often induced using intense laser light and specialized buffers or UV radiation. Recently, so-called self-blinking dyes that switch spontaneously between an open, fluorescent "on" state and a closed, colorless "off" state were introduced. Here, we exploit the synergy between super-resolution optical fluctuation imaging (SOFI) and spontaneously switching fluorophores for 2D and 3D imaging. SOFI analyzes higher order statistics of fluctuations in the fluorophore emission instead of localizing individual molecules. It thereby tolerates a broad range of labeling densities, switching behavior, and probe brightness. Thus, even dyes that exhibit spontaneous blinking characteristics that are not suitable or suboptimal for single molecule localization microscopy can be used successfully for SOFI-based super-resolution imaging. We demonstrate 2D imaging of fixed cells with almost uniform resolution up to 50-60 nm in 6th order SOFI and characterize changing experimental conditions. Next, we investigate volumetric imaging using biplane and eight-plane data acquisition. We extend 3D cross-cumulant analysis to 4th order, achieving super-resolution in 3D with up to 29 depth planes. Finally, the low laser excitation intensities needed for single and biplane self-blinking SOFI are well suited for live-cell imaging. We show the perspective for time-resolved imaging by observing slow membrane movements in cells. Self-blinking SOFI thus provides a more robust alternative route for easy-to-use 2D and 3D high-resolution imaging.