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In this paper, we developed a theoretical model for the photothermal deflection technique in order to investigate the electronic parameters of three-layer semiconductor structures. This model is based on the resolution of thermal and photogenerated carrier diffusion-wave equations in different media. Theoretical results show that the amplitude and phase of the photothermal deflection signal is very sensitive to the nonradiative recombination parameters. The theoretical model is applied to one layer of InAs quantum dots (QDs) inserted in GaAs matrix InAs/GaAs QDs in order to investigate the QD density effects on nonradiative recombination parameters in InAs through fitting the theoretical photothermal beam deflection signal to the experimental data. It was found that the minority carrier lifetime and the electronic diffusivity decrease as functions of increasing InAs QD density. This result is also related to the decrease in the mobility from 21.58 to 4.17 (±12.9%) cm2/V s and the minority carrier diffusion length from 0.62 (±5.8%) to 0.14 (±10%) μm, respectively. Furthermore, both interface recombination velocities S 2 / 3 of GaAs/InAs (QDs) and S 1 / 2 of InAs (QDs)/GaAs increase from 477.7 (±6.2%) to 806.5 (±4%) cm/s and from 75 (±7.8%) to 148.1 (±5.5%) cm/s, respectively. [ABSTRACT FROM AUTHOR]

We investigate an efficient spatial enantioseparation method of chiral molecules in cyclic three-level systems coupled with three optical fields using optically induced forces. When the overall phase differs by π between two enantiomers, significant variations in the magnitude and direction of the optically induced forces are observed. The manipulation of the center of mass of chiral molecules in optical fields can be achieved through the induced gauge force, primarily generated from the variations in the chirality-dependent scalar potentials created by the three inhomogeneous laser fields. By appropriately configuring the system, we can completely separate the slow spatial and fast inner dynamics, making instantaneous eigenstates of the inner Hamiltonian independent of the transverse profiles of the laser beams. Compared to previous methods, which required adiabatic conditions to be satisfied, the proposed method overcomes the limitations of the adiabatic approximation by utilizing a specific system configuration. This allows for increased flexibility in the transverse profiles of the laser beams and relaxes the constraints on the velocity of chiral molecules, leading to significantly greater spatial separations achievable across a broader range of parameters. [ABSTRACT FROM AUTHOR]

Ultrafast laser technology presents the unique capacity to process glass materials with an outstanding processing quality; however, combining high quality and high throughput is still a crucial issue because glass is brittle and highly heat sensitive. One strategy to overcome this limitation is to split in space the main laser beam into multiple beams for process parallelization. In the present paper, the simultaneous interaction of several femtosecond laser beams at the surface of fused silica targets is addressed experimentally and theoretically. This work is devoted to highlight the beams cooperation for inducing stress in the material. The experiment consists in irradiating the target with multiple laser pulses with a wavelength of 1030 nm and a duration of 500 fs. The induced stress is observed through post-mortem cross-polarized microscopy. A multiscale and multiphysics model describing laser energy deposition into the material and its mechanical response is developed. The influence of various laser parameters is studied: number and position of laser beams, repetition rate, and fluence. Both experimental and modeling results, which are in a good agreement, show significant cooperative effects for stress formation with large enough laser energy deposition, possibly leading to detrimental cracks. [ABSTRACT FROM AUTHOR]

A complete simulation chain for the laser-based generation of a microfocus-size gamma ray beam of multi-MeV energy range able to produce radiographic images has been developed. The major interactions needed to obtain such a beam are treated individually. Particle-in-cell is used to study the generation of the electron beam through laser wake-field acceleration (LWFA), and Geant4 is employed for the Bremsstrahlung photon emission and for testing the imaging capabilities of the generated gamma beam. The paper presents detailed discussions about the implementation of each simulation, along with the results obtained. The structure of the article walks through the LWFA of up to 100 MeV electron beam, followed by its attenuation through a tantalum foil generating a 300 μ m spot size photon beam, later used for imaging of a thick lead test-object, assessing a 100 μ m resolution, and confirming the simulated imaging setup suitability for non-destructive testing applications of thick high-density objects. An analysis of the quality control parameters for the generated image along with discussions of possible improvements is also included. [ABSTRACT FROM AUTHOR]

Modulation of the refractive index in a medium by external stimuli enables fast and reversible control of light propagation. This technology for controlling light has led to new discoveries in a wide range of research fields from physics to life sciences and has played a major role in the development of photonics devices. In this article, we focus on ultrasound as an external stimulus and have devised a method to control the refractive index of a medium using ultrasound. Our research group has previously discovered that a giant refractive-index gradient (Δn on the order of 10−2) was induced when water was irradiated with high-frequency (100 MHz range), high-intensity (on the order of MPa) ultrasound. Here, we report ray-tracing simulations in a medium with a refractive-index gradient induced by ultrasonic radiation. A numerical model of the refractive-index gradient was developed based on the experimental data, and ray-tracing simulations were performed using the Euler–Lagrange equation. The ray-tracing simulation results were close numerically to the profiles of the laser beam observed in the experiment when the laser beam was incident on the refractive-index-gradient medium. [ABSTRACT FROM AUTHOR]

We report on the quantitative nondestructive analysis of the natural isotopic abundances of hafnium and tungsten elements using nuclear resonance fluorescence. Metallic samples of hafnium and tungsten were irradiated to six quasi-monochromatic γ -ray beams generated by laser Compton scattering in the energy range of 2.4–3.2 MeV. Multiple nuclei were simultaneously excited at each of the six γ -ray beam energies. A high-purity germanium detector array detected deexcitations of the nuclei. In total, 51 transitions were unprecedentedly employed to estimate the isotopic abundances of heavy elements nondestructively. The estimated abundances of three hafnium isotopes and three tungsten isotopes are consistent with standard known natural abundances within the experimental uncertainties. The deviation from the standard values ranges from 0.18 % to 1.36 %. [ABSTRACT FROM AUTHOR]

Interaction of intense ultrashort laser pulse with gases generates a transient spatiotemporal electron density distribution via field ionization, which may lead to the spatiotemporal reshaping of the pulse, viz., its beam profile, pulse width, etc. Here, we present an experimental study on ultrashort laser pulse interaction with argon gas sheath in an ionization saturation intensity regime (∼1015–1017 W/cm2). The present investigation has been performed using a 6 mJ, 1 kHz, and 55−60 fs Ti:Sapphire laser pulse interaction with a ∼2.5 mm long argon sheath. After the laser gas interaction, the laser spatial profile exhibits a multi-ring structure around a central maximum spot. Laser gas interaction parameters, such as laser intensity, gas pressure, etc., affect the ring pattern significantly. Under optimum parameter conditions, the laser pulse has two rings in spatial profile, and the pulse width of the central spot is self-compressed to ∼35 fs. A theoretical calculation reveals that the laser beam's spatiotemporal profile evolves as it propagates inside the gas sheath. The calculation also demonstrates that the gas ionization profile plays a crucial role in the spatiotemporal reshaping and self-compression of the laser beam. The calculation also shows that the generation of concentric ring patterns in the spatial profile is mainly due to the ionization of argon atoms into Ar+, Ar2+, and Ar3+ species in the interaction region. Such self-compressed laser pulses with concentric ring beam profiles may be useful for high-harmonic generation and shorter attosecond pulse trains. [ABSTRACT FROM AUTHOR]

Photothermal spectroscopy, and more specifically photothermal interferometry (PTI), is a highly sensitive technique for measuring gas and aerosol concentrations. Numerous implementations of different PTI configurations have demonstrated the versatility of the technique. This theoretical study presents a comprehensive analysis and an optimization of the PTI optical path length (OPL) amplitude using characteristic times. We investigate how the OPL amplitude depends on the dimensions and orientations of the interferometer laser beam and the continuous-wave excitation laser beam. This analysis quantifies the impact of advection on the OPL amplitude based on the relative orientation of the two laser beams and the gas flow direction. It is analytically shown that the possibilities for photothermal OPL amplitude optimization are limited when thermal diffusion is dominant. Theoretically, advection has the potential to double or cancel the OPL amplitude, depending on the specific configurations. In summary, we provide an in-depth understanding of the design and parameter considerations required when tailoring and optimizing a PTI sensor for different fields of applications. [ABSTRACT FROM AUTHOR]

In this study, we conducted successful experiments on ethylenediamine sulfate (EDS), an organic compound, to investigate its enantioselectivity in chiral crystallization. We employed optical trapping with circularly polarized laser beams, using a continuous wave laser at 1064 nm. By focusing the laser at the air–solution interface of a heavy water-saturated EDS solution, the formation of sub-micrometer-sized chiral EDS crystals was verified. Two generated enantiomorphs (d-crystal and l-crystal) were identified by the rotating analyzer method. The enantioselectivity in the chiral crystallization of EDS was assessed through 30 to 60 times experiments conducted under various conditions of laser powers and polarization modes, utilizing the count of generated crystals for each enantiomorph in the evaluation. Circularly polarized lasers at a specific power created an imbalance in the generation probability of the enantiomorphs, resulting in crystal enantiomeric excess values of 23% and −30%. The enantioselectivity mechanism was explored from two perspectives: refractive index differences of two enantiomorphs and 3D helical optical forces. Study of the thermodynamic mechanism was insufficient to explain the outcomes. Conversely, the 3D helical optical force mechanism revealed that the forces acting on EDS clusters in solution induced helical fluid motion, driving EDS nucleation, with the helicity of fluid motion determining the crystal's chirality. This approach will present new insights into chirality in industrial and research fields, with potential applications in regard to improving optical resolution and addressing the origin of homochirality. [ABSTRACT FROM AUTHOR]

Molecular lasers pumped by quantum cascade laser (QCL) open new possibilities for THz generation and its numerous applications, in particular, for high resolution molecular spectroscopy. In this article, a THz water laser pumped by a mid-infrared QCL was demonstrated using the broad tunability of the pump laser. Twenty D 2 O laser lines were measured under a continuous wave pumping regime, in a spectral range expending from 63 to 177 cm − 1 (1.9–5.3 THz), and with an output power ranging from tens to hundreds of μ W. This letter contains a description of the experimental setup used to produce the THz laser radiation and a comparison of the measured output power with a molecular gain factor used to sort out the most favorable laser lines. In addition to the measured laser transitions, a complete list of laser frequencies together with their corresponding molecular gain is given in the supplementary material, for both H 2 O and D 2 O isotopologues excited in their bending and stretching vibrational states. [ABSTRACT FROM AUTHOR]

The described method is intended for application as a diagnostic tool for a nonstationary, short-lived plasma (in particular, for the laser-produced plasma). It is based on taking into account the lifetime of a laser-produced plasma, which is so short (several nanoseconds) that it is not enough for the ionization equilibrium to be established. Among mechanisms leading to appearance of an ion with a given charge Z in the plasma, only the electron-collisional ionization is considered, because contributions of other phenomena turn out to be negligible. The method is discussed as an example of a plasma excited on the Xe gas-jet target. The necessary collisional cross sections of ions from+7Xe to+16Xe have been calculated specifically for this study using a quantum-mechanical numerical simulation, with its principles and features being also presented in the paper. To demonstrate capabilities of the method, it has been applied to one of the experimental cases when the plasma was produced by the laser beam focused on the Xe gas-jet target. The time-integrated energy of laser radiation absorbed in the plasma was measured, and the absorption coefficient, μ, was derived from it with a correction for the plasma lifetime, which was several times shorter than the laser pulse. Using the method described here, the values of ⟨ Z ⟩ and then μ were calculated as a function of temperature. The time-averaged plasma temperature, T, in the above-mentioned experiment was believed to be equal to that at which the calculated and experimentally determined values of μ coincided. The following results were obtained: T = 42 eV, ⟨ Z ⟩ = 10.2. [ABSTRACT FROM AUTHOR]

A study of residual mechanical stresses in the surface layer of the HgCdTe/CdTe/ZnTe/GaAs structure based on the registration of the second harmonic signal characteristics of reflected IR laser radiation from the surface of the studied sample passed through a nonlinear crystal was carried out. It is shown that such a sensitive method makes it possible to obtain information about the anisotropy of the polarization of the reflected radiation, caused by the residual deformation. Observations of the fine structure of the angular sweep of the second harmonic signal suggest a complex structure of residual stresses related to the presence of misoriented areas. The results were compared with data obtained from measurements of the azimuthal dependence of the self-reflected second harmonic signal from the sample surface. [ABSTRACT FROM AUTHOR]

In the current work, laser thermal treatment of the FeSiB amorphous foil with a single linear laser track was carried out. The resultant microstructure and phase evolution were examined with the aid of x-ray diffraction, differential scanning calorimetry, and site-specific transmission electron microscopy. The laser power was kept constant at 100 W, whereas, laser beam scanning speeds were varied in the range of 500–235 mm/s, generating corresponding laser fluences of 0.42–0.91 J/mm 2 on the sample surface. Laser fluences of up to 0.48 J/mm 2 structurally relaxed the FeSiB foil, retaining the amorphous structure. Laser fluences of higher than 0.48 J/mm 2 led to partial crystallization of FeSiB amorphous foils. The crystallite sizes were in the range of 11–31 nm (laser fluence of 0.49–0.91 J/mm 2). α -FeSi formed as a major phase of partial crystallization while its quantity steadily increased from 3.6 to 46 vol. % with laser fluence (laser fluence 0.49–0.91 J/mm 2). Fe 2 B formed in recognizable quantities (≥ 2%) for laser fluences ≥ 0.53 J/mm 2. Laser fluences leading to structural relaxation and evolution of predominantly α -FeSi phase exerted minimal effects on ratios of intrinsic coercivities to saturation compared to the as-cast FeSiB amorphous foil. On the contrary, formation of Fe 2 B in significant quantities (≥ 2 %) led to the steady increase in intrinsic coercivities and remanence to saturation ratios as a function of laser fluence indicating a loss in soft magnetic characteristics. Nonetheless, continuous increase in fractions of α -FeSi with laser fluence led to a steady improvement in saturation magnetostriction of the FeSiB foil. [ABSTRACT FROM AUTHOR]

We report on the observation of a nonlinear intensity dependence of the terahertz radiation-induced ratchet effects in bilayer graphene with asymmetric dual-grating gate lateral lattices. These nonlinear ratchet currents are studied in structures of two designs with dual-grating gates fabricated on top of boron nitride encapsulated bilayer graphene and beneath it. The strength and sign of the photocurrent can be controllably varied by changing the bias voltages applied to individual dual-grating subgates and the back gate. The current consists of contributions insensitive to the radiation's polarization state, defined by the orientation of the radiation electric field vector with respect to the dual-grating gate metal stripes, and the circular ratchet sensitive to the radiation helicity. We show that intense terahertz radiation results in a nonlinear intensity dependence caused by electron gas heating. At room temperature, the ratchet current saturates at high intensities of the order of hundreds to several hundreds of kW cm − 2 . At T = 4 K, the nonlinearity manifests itself at intensities that are one or two orders of magnitude lower; moreover, the photoresponse exhibits a complex dependence on the intensity, including a saturation and even a change of sign with increasing intensity. This complexity is attributed to the interplay of the Seebeck ratchet and the dynamic carrier-density redistribution, which feature different intensity dependencies and nonlinear behavior of the sample's conductivity induced by electron gas heating. The latter is demonstrated by studying the THz photoconductivity. Our study demonstrates that graphene-based asymmetric dual-grating gate devices can be used as terahertz detectors at room temperature over a wide dynamic range, spanning many orders of magnitude of terahertz radiation power. Therefore, their integration together with current-driven read-out electronics is attractive for the operation with high-power pulsed sources. [ABSTRACT FROM AUTHOR]

This paper is devoted to the experimental study of the characteristics of a continuous optical discharge (COD) sustained by high power continuous wave laser radiation at a wavelength λ = 1.08 μ m in high pressure argon. New data on the COD threshold laser power dependence of argon pressure in the range 20–50 bar is obtained. The COD threshold laser power is shown to be in good agreement with the data obtained by other authors and theoretical evaluations provided the contribution of plasma energy loss due to thermal radiation is taken into account properly. The maximum plasma temperature was estimated to be 20–21 kk or higher, favorable to obtain high UV spectral radiance. A study of the convective plume oscillations around COD in argon has been carried out. It is found that in the pressure range 25–35 bars the growth of the laser radiation power leads to a decrease in convection oscillation frequency from 33 to 29 Hz, while the radius of the convective plume grows accordingly. The oscillation frequency ν and characteristic radius of the convective plume r 0 were found to obey the similarity relation ν = 0.5 g / 2 r 0 previously established in experiments with COD in xenon. These results are promising for using COD in argon as a high brightness broadband UV radiation source. [ABSTRACT FROM AUTHOR]

Laser shock forming (LSF) is a novel plastic forming process which utilizes a laser-induced shock wave to deform metal sheet to 3D configurations. Quantitative evaluation of the deformation in LSF is of great importance to understand the forming mechanism and achieve the high precision. In this paper, an analytical model was proposed to predict the deformation of a circular plate in laser shock bulging process. Models showed that the deformation is related to material parameters such as the impedance, density, yield strength of the metal target, geometric parameters such as the plate thickness and die radius, and processing parameters such as the energy, radius and pulse duration of the laser beam. The deformation profiles and the maximum deformation height calculated by the analytical model agree with those of experiment, which validate the rationality of the constructed models. The maximum deformation height increases with an increase of laser energy and decreases with increasing plate thickness. [ABSTRACT FROM AUTHOR]

Metasurfaces have recently gained significant attention due to the strong capacity in light field manipulation. However, most traditional metasurfaces are fabricated on rigid substrates, which fix their functionality after fabrication and limit their applications in dynamic measurement fields. In this work, we designed and fabricated a silver metasurface embedded in a stretchable substrate for sensing applications. This metasurface can generate different point cloud patterns under varying stretch ratios when illuminated by a laser beam. By collecting and analyzing the patterns, we can precisely reconstruct the deformation of the metasurface. Furthermore, the sample exhibits excellent performance under incident light of various wavelengths. These results pave the way for developing microdevices with novel capabilities based on flexible metamaterials. [ABSTRACT FROM AUTHOR]

2D metal/semiconducting heterostructures have attracted extensive attention for potential applications in future electronic and optoelectronic devices. However, the simple and fast preparation of patterned metal/semiconducting heterostructures with controllable channel lengths still faces challenges. Here, a simple and reliable laser patterning method for preparing patterned lateral/vertical 1T/2H VS2/MoS2 metal/semiconducting heterostructures is reported. Specifically, site‐selective etching of VS2 can be realized through the combination of laser radiation and acid solution etching. Further, pre‐patterned VS2 nanoplates with edge dangling bonds can offer effective nucleation points for the lateral epitaxial growth of MoS2, thus generating patterned VS2‐MoS2 lateral heterostructures. The laser processing method can further be used to create patterned VS2/MoS2 vertical van der Waals (vdWHs), which can only selectively etch the upper layer VS2 while maintaining the intrinsic structure of the bottom layer MoS2. The obtained patterned VS2/MoS2 vdWHs show a similar channel length of ≈420 nm, and the VS2 vdW contact MoS2 transistor is fabricated, delivering an On‐state current of 4.01 µA/µm, and carrier mobility of 3.56 cm2 s−1 V−1. This approach is also general for preparing patterned VSe2, VSe2/WSe2 heterostructures. [ABSTRACT FROM AUTHOR]

Pulsed polarized vortex beams, a special form of structured light, are generated by tailoring the light beam spatiotemporally and witness the growing application demands in nonlinear optics such as ultrafast laser processing and surface plasma excitation. However, existing techniques for generating polarized vortex beams suffer from either low compactness due to the use of bulky components or limited controlment of pulse performance. Here, an all-fiber technique combining plasmonic metafibers with mode conversion method is harnessed to generate high-performance pulsed polarized vortex beams. Plasmonic metafibers are utilized as saturable absorbers to produce Q-switched pulses with micro-second duration, while the offset splicing method is employed to partially convert the fundamental transverse mode (LP 01 ) to higher-order mode (LP 11 ). Eventually, a polarized vortex beams laser is achieved at the telecom band with a repetition frequency of 116.0 kHz. The impact of geometrical parameters including period of metafibers and offset of splicing on the spatiotemporal properties of pulsed polarized vortex beams is systematically investigated. Our findings could pave the way for design, control and generation of all-fiber pulsed polarized vortex beams, and also offer insights into the development of other types of structured laser sources. [ABSTRACT FROM AUTHOR]

The bidirectional reflectance distribution function (BRDF) can effectively characterize the reflectance properties of a target, which can be used to correct infrared remote sensing data and improve the accuracy of remote sensing measurements. When the surface temperature changes, the reflectance characteristics of the target usually change, and it is necessary to carry out BRDF measurements under variable temperature conditions. In this paper, a variable-temperature infrared BRDF measurement system based on a robotic arm is developed to realize high-resolution wide-temperature region measurement of BRDF. To improve the measurement accuracy, the shaping optical path was used to expand the laser beam, combined with the laser level to accurately adjust the three-dimensional coordinates of the robotic arm, and the dichotomy method is used to calibrate the detector nonlinearly. A portable heater suitable for the mechanical arm corner mechanism is developed, and fast and high-precision temperature control is realized by proportional integral derivative (PID) control. The specular and diffuse BRDF distributions were measured at room temperature to verify the effectiveness of the system. The BRDF distribution of SUS314 stainless steel samples with different roughness is measured during two temperature increases from 20 °C to 1000 °C, and the changing rule of BRDF under variable temperature environment is summarized, which provides technical support for evaluating the optical properties of high-temperature materials and improving the measurement accuracy of remote sensing data. [ABSTRACT FROM AUTHOR]

We consider the stability of bound‐state solutions of a family of regularized nonlinear Schrödinger equations which were introduced by Dumas et al. as models for the propagation of laser beams. Among these bound‐state solutions are ground states, which are defined as solutions of a variational problem. We give a sufficient condition for existence and orbital stability of ground states, and use it to verify that ground states exist and are stable over a wider range of nonlinearities than for the nonregularized nonlinear Schrödinger equation. We also give another sufficient and almost necessary condition for stability of general bound states, and show that some stable bound states exist which are not ground states. [ABSTRACT FROM AUTHOR]

In Laser decal transfer process, the materials are printed in micron-sized dots without changing its phase from thin film coated substrate (donor substrate). The pulsed laser irradiates the donor substrate opposite to the coated side and transfers the material in the same phase to another substrate kept very close to the donor substrate. The process has shown its potential for printing microsensors without any changes in physical and functional properties during the printing process for the electronics components. Generally, ZnO-based patterned structure is still challenging for the existing manufacturing techniques without hampering its functionality in the sensing application. In this work, an attempt has been made to print ZnO structure in solid phase using maskless µ-3D printing using a long-pulsed CO2 laser. A two-dimensional numerical model in COMSOL Multiphysics is developed to estimate the temperature induced by the laser irradiation on the sacrificial layer, and energy conservation is applied to estimate the particle's velocity. A deformed mesh geometry is used to predict the ablation depth of the sacrificial layer after the laser irradiation. The deformed geometry shows the ablated area in the sacrificial layer, and the temperature induces a different time frame. The ZnO ceramic film is coated on the sacrificial layer followed by the laser µ-3D printing of ZnO on silicon wafer using CO2 laser at three laser fluence, i.e., 530 mJ/cm2, 1030 mJ/cm2, and 1530 mJ/cm2 with 90% pulse overlap. The ejection of ZnO from substrate is visualized using a high-speed camera by shadowgraphy techniques. The ejection mode is defined based on the deviation of the particle from the laser beam direction. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is increasingly viable for the high-volume production of complex parts due to material and time savings, weight reduction, design optimization, and the development of new materials. Laser metal deposition (LMD), a specific AM process, offers high build rates and larger deposition volumes, making it cost-effective for industries such as aerospace and defense, which benefit from increased productivity and the ability to repair large components. Martensitic stainless steels are valued for their mechanical properties in these sectors, despite the challenges of maintaining these properties during LMD deposition. The purpose of this study was to evaluate the deposition parameters for laser cladding using LMD with AISI 431 martensitic stainless steel powder and to analyze the morphological aspects. Microstructural evolution was assessed using optical and electron microscopy, with samples produced by varying laser power (800, 1000, 1400, 1600 W) and scanning speed (9, 14, 16 mm/s). The results showed dilution values between 10 and 27% for power values of 1400 and 1600 W for all laser beam velocities tested. Microstructural characterization revealed martensite and ferrite phases in the deposits. Increasing the scanning speed resulted in higher dilution and wettability and decreased the height/width ratio of the deposits. The laser deposition parameters also affected the solidification parameters (G/R) and the cooling rate (G × R), which are critical for understanding the resulting microstructure and hardness of the deposits. This study highlights the importance of considering geometric and microstructural aspects in LMD for AISI 431 steel to ensure high productivity and optimal performance and demonstrates the potential of the LMD process for the deposition of martensitic stainless steel. [ABSTRACT FROM AUTHOR]

TianQin is expected to deploy three spacecraft in Earth orbit at the altitude of about 1 × 108 m to form an equilateral triangular constellation with arm lengths of about 1.7 × 108 m. It is aimed at detecting gravitational waves in the frequency range from 0.1 mHz to 1 Hz by means of high sensitive laser ranging interferometry with pathlength measurement noise below 1 pm/Hz1/2. The long-range propagation of beam in the intersatellite laser ranging interferometry between the three spacecraft results in a non-negligible time delay of 0.58 s. Therefore, there is an angular difference between the optimal outgoing and incoming laser beam of laser ranging interferometry on each spacecraft, which is denoted as the point-ahead angle. Due to the relative motion between the three spacecraft, the point-ahead angle of TianQin constellation is approximately 22.96 μrad with a dynamic variation range of ±24.71 nrad. Point-ahead-angle mechanism is a fine steering mirror used for point-ahead angle compensation to diminish the beam pointing error, thus to maintain the intersatellite laser link as well as to diminish the tilt-to-length coupling noise, which are vital to the gravitational wave detection. Both the static and dynamic point-ahead angle compensation strategies can be used in TianQin and the selection of the two is based on minimizing the total point-ahead-angle-related tilt-to-length coupling noise. In this paper, a criteria for selection of the two strategies are proposed by establishing a model of point-ahead-angle-related tilt-to-length coupling noise as well as a corresponding evaluation function for calculation and comparison. The results indicate that the dynamic compensation strategy is the optimal choice only when the first-order tilt-to-length coupling coefficient of point-ahead-angle mechanism is less than 6.4 × 10−9 m/rad, otherwise the static compensation strategy should be used. The proposed criteria, as well as the model and the requirement for point-ahead-angle mechanism, can serve as a common theoretical basis in laser ranging interferometry applications. • Criteria for selection of point-ahead angle compensation strategies. • Minimize tilt-to-length coupling noise in intersatellite laser interferometry. • Quantitative comparison of tilt-to-length noise in different compensation strategies. • Static compensation strategy is more appropriate in TianQin according to the criteria. [ABSTRACT FROM AUTHOR]

Laser-assisted turning (LAT) involves locally heating a rotating workpiece using a focused laser beam before the removal of material. A key aspect in optimising productivity with laser-assisted turning is understanding the thermal relationship between laser heating, the improved material removal rate, and machinability. Consequently, in this paper, a thermal heating and laser-assisted turning finite element model and experiments were conducted to assess the machinability of an Al/SiC p MMC workpiece, considering the circumferential location of the laser beam from the cutting point. The results confirm that laser power and cutting velocity influence the temperature profile from the laser spot to the tool point and the heat-affected depth. Positioning the cutting tool closer to the laser spot effectively reduces the Von Mises stress during cutting at higher cutting temperatures. At the same time, the experiment indicates an increased risk of directly heating the tool, which can affect the integrity of the cutting tool. The work further reveals that at specified cutting velocities, lower specific cutting energy improves the tool condition and surface quality of the machined parts. Based on a range of material removal rates and laser-specific energy density, a new criterion for optimal laser-tool circumferential distance was determined. Establishing this distance can act as a guide for the laser-assisted turning of Al/SiC p metal matrix composites and potentially other materials. [ABSTRACT FROM AUTHOR]

We report an application of a pulsed ultraviolet (UV) laser (λ = 355 nm) in producing translucent Si solar cells. This process efficiently generates a densely packed microhole array on a fully fabricated Si P‐N junction solar cell in just a few minutes. Herein, prototype cells with a nominal microhole diameter of 23 μm with a spacing between 60 and 300 μm are fabricated. High‐resolution electron‐beam microscopy reveals that the UV laser beam introduces amorphized silicon oxide (SiOx) in proximity to the patterned microholes via localized heating in air. Quantitative photovoltaic (PV) analysis shows a decline in the open‐circuit voltage (Voc) and the fill factor (FF) of the cells with the increase in the microhole density, likely due to the P‐N junction damage during the laser beam irradiation. Despite the reduction in Voc and FF, the solar cells retain a short‐circuit current density (Jsc) above 90% without post‐processing. The inherent microhole geometry associated with the laser beam profile allows multiple light scattering within the confined microhole structure, enhancing the translucency of the cells. While further development is required for optimization, these findings support the potential use of UV laser beams for fast and scalable production of translucent solar cells. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to investigate the effect of different beam distance by understanding laser beam influence on solder joint quality. The utilisation numerical-based simulations and experimental validation will help to minimise the formation of micro void in PTH that can lead to cracks and defects on passive devices. Design/methodology/approach: The research uses a combination approach of numerical-based simulation using Finite Volume Method (FVM) and experimental validation to explore the impact of different laser beam distances on solder joint quality in PTH assemblies. The study visualises solder flow and identifies the optimal beam distance for placing a soldering workpiece and a suitable tolerance distance for inserting the solder wire. Findings: The simulation results show the formation of micro void that occurs in PTH region with low volume fraction and unbalance heat concentration profile observed. The experimental results indicate that the focus point of the laser beam at a 99.0 mm distance yields the smallest beam size. Simulation visualisation demonstrates that the laser beam's converging area at +4.6 mm from the focus point which provides optimal tolerance distances for placing the solder wire. The high-power laser diode exhibits maximum tolerance distance at 103.6 mm from the focus point where suitable beam distance for positioning of the soldering workpiece with 50% laser power. The simulation results align with the IPC-A-610 standard, ensuring optimal filling height, fillet shape with a 90° contact angle and defect-free. Practical implications: This research provides implications for the industry by demonstrating the capability of the simulation approach to produce high-quality solder joints. The parameters, such as beam distance and power levels, offer practical guidelines for improving laser soldering processes in the manufacturing industry. Originality/value: This study contributes to the field by combining high-power laser diode technology with numerical-based simulations to optimise the beam distance parameters for minimising micro void formation in the PTH region. [ABSTRACT FROM AUTHOR]

With the aid of the Caputo fractional derivative, this study constructs a novel mathematical model of magneto-thermoelasticity to investigate the transient phenomena for a fiber-reinforced rotating half-space under the influence of pulsed laser as heat source and inclined load in the context of refined three-phase-lag (TPL) Green–Naghdi (GN) models of generalized thermoelasticity, which is defined in an integral form of a common derivative on a slipping interval by incorporating the memory-dependent heat transfer. Together with the temperature gradient (Seebeck effect) and charge density influence, the generalized magneto-thermoelasticity model's equations now include the modified Ohm's law. An intense non-Gaussian laser beam heats the bounding plane's surface. By using the normal mode analysis, the analytical expressions of the thermophysical quantities are produced in the physical domain. All physical quantities have been graphically depicted for different GN models (refined GN-II and GN-III models) to indicate the effect of memory-dependent derivative, Seebeck parameter, rotation and reinforcement of the medium under the influence of inclined load and pulsed laser. [ABSTRACT FROM AUTHOR]

Quantum cascade lasers (QCLs) in the mid-infrared (MIR) hold significant potential for widespread applications in both military and civilian contexts. However, the utility of present single-chip QCLs is hampered by issues such as low output power and subpar beam quality. This study addresses these limitations by employing spectral beam combining (SBC) based on a diffraction grating, with an aim to enhance both power and beam quality of MIR QCLs. Coaxial power synthesis of three single-chip QCLs (around 4.75 μm) is achieved experimentally, importantly, the beam quality did not decrease after combining, essentially maintaining the same quality as before combining. It is proposed that there are four main factors affecting the combining efficiency, namely operating optical power (or driving current) of the chips, individual differences in QCL chips, diffraction grating, and reflectivity of feedback mirror, and their effects on the combining efficiency are discussed separately. This study confirms that SBC is an effective way to obtain high-power and high-beam quality MIR QCL sources, and lays a research foundation for more beam spectral combining. [ABSTRACT FROM AUTHOR]

Nanophotonics techniques, driven by optical microscopy, enable high‐capacity data recording and readout, yet ensuring data security demands versatile, multi‐stimuli activatable media. Lanthanide ion‐doped upconversion nanoparticles hold promise for these applications by fine‐tuning upconversion luminescence emission. While chemical methods customize this emission with meticulous adjustments, optical methods face challenges such as high laser beam intensities, setup complexity, and wavelength limitations. Efficiently modulating upconversion luminescence emission requires multi‐stimuli methods or integrating upconversion nanoparticles with responsive materials. Here, dual‐stimulus thermo‐optical activation and optical microscopy are used to achieve sub‐micrometer ultrahigh upconversion luminescence emission tuning in newly developed hybrid organic–inorganic upconversion nanocomposites for high‐capacity and secure data storage and anticounterfeiting. Thermal stimulus (activation I) facilitates a 102‐fold increase in absorption, promoting the formation of an inorganic network and complex. Optical stimulus via focused 460‐nm femtosecond laser beam irradiation (activation II) enhances absorption by fivefold through sub‐micrometer photo‐polymerization bit recording. The method achieves a 92% decrease of 450‐nm upconversion luminescence emission intensity after activation I and over 90% quenching of this emission after activation II, enabling sub‐micrometer bit readout under 980‐nm continuous‐wave excitation laser beam irradiation. This work demonstrates the potential for high‐capacity and secure data storage, anticounterfeiting, high‐security encryption, and high‐resolution display. [ABSTRACT FROM AUTHOR]

The treatment of keloids, particularly in high‐tension areas, is challenging due to their extension beyond the original wound boundaries and high recurrence rates, thereby rendering traditional treatments ineffective. In this study, we investigated the effectiveness of a novel single‐stage treatment approach that combined acellular dermal matrix (ADM) with keloid‐specific epidermal skin grafting. To further prevent recurrence after neo‐skin formation, the treatment was followed by fractionated laser and radiation therapy (LCR). Seven patients with high‐tension keloids, including one with keloids at two locations, were treated and followed‐up for an average of 15.9 months. The patients showed significant improvements in wound healing and skin appearance, with a marked reduction in the Patient and Observer Scar Assessment Scale (POSAS) (scores from 91.1 ± 5.6 to 23.8 ± 6.1 (p < 0.001)). This approach effectively minimizes tension, reduces the likelihood of keloid recurrence, and serves as a viable alternative to conventional methods that often involve challenges related to donor‐site acquisition. No recurrence was observed during the follow‐up period, indicating a promising innovation in the management of extensive keloids and offering improved healing and esthetic outcomes, particularly in high‐tension areas. [ABSTRACT FROM AUTHOR]

ABSTRACT Manganese oxides/oxyhydroxides (MnOx) are based on Mnn+O6 and Mnn+O4 polyhedra arranged such as to form compact, channel or layered structures. In geology, they are precious archives of past redox conditions for palaeoclimatic reconstructions; in material sciences, they are used for a variety of applications, from pigments to environmental remediation and energy storage. Thus, the fast, remote and non‐destructive identification of MnOx is critical in several disciplines. Micro‐Raman spectroscopy is often used for this purpose, although a systematic characterization of their stability under the laser beam is still lacking. In this work, we present our results on the behaviour of the most common MnOx having compact and channel structures when a 532‐nm laser with intensity between ~23 μW/μm2 and ~36.8 mW/μm2 is used. The compact structures of manganosite (NaCl‐like) and hausmannite (spinel‐like) are stable up to ~36.8 mW/μm2. The stability of oxides with channel structures depends on channel size, charge of channel cations and valence state of Mn. Hausmannite is the final degradation product of all MnOx with channel structures, irrespective of the starting phase. Pyrolusite, manganite, hollandite and romanéchite are relatively stable under the laser beam, and the transition to the spinel structure occurs above 2.5 mW/μm2 while the degradation of cryptomelane and todorokite starts ~226 μW/μm2. The analysis of MnOx thus needs very accurate experimental conditions to avoid misleading and incorrect phase identifications. Based on our data, we propose an analytical protocol for a proper characterization of these minerals via Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Optical tweezers revolutionized the manipulation of nanoscale objects. Typically, tunable manipulations of optical tweezers rely on adjusting either the trapping laser beams or the optical environment surrounding the nanoparticles. Here, tunable and switchable trapping using nanoparticles made of a phase‐change material (vanadium dioxide or VO2) are achieved. By varying the intensity of the trapping beam, transitions of the VO2 between monoclinic and rutile phases are induced. Depending on the nanoparticles' sizes, they exhibit one of three behaviors: small nanoparticles (in the settings, radius <0.12$<0.12$ wavelength λ$\lambda$) remain always attracted by the laser beam in both material phases, large nanoparticles (>0.22λ$>0.22 \lambda$) remain always repelled. However, within the size range of 0.12−0.22λ$0.12\!-\!0.22\lambda $, the phase transition of the VO2 switches optical forces between attractive and repulsive, thereby pulling/pushing them toward/away from the beam center. The effect is reversible, allowing the same particle to be attracted and repelled repeatedly. The phenomenon is governed by optical Mie modes of the nanoparticles and their alterations during the phase transition of the VO2. This work provides an alternative solution for dynamic optical tweezers and paves a way to new possibilities, including optical sorting, light‐driven optomechanics and single‐molecule biophysics. [ABSTRACT FROM AUTHOR]

Multiscale parameter optimization for laser peen forming (LPF) on 6005A-T6 aluminum alloy plates was conducted through a combination of simulation and experimentation. By obtaining the optimal parameter, this study aims to explore the constrained deformation and forming laws of the integral stiffened plates. Detailed descriptions were provided regarding the dynamic response process and transient behavior of aluminum alloy plates under ultrahigh strain rates, along with an in-depth analysis of the stress evolution. The results reveal that laser beam diameter and laser beam energy can achieve large range forming, while the number of tracks facilitates the precise deformation adjustment. During the 12-track LPF process, there is an overall upward trend in deformation values accompanied by a dynamic increase in the bend curvature. After static relaxation, the deformation value recovers to 55.2% of the final bending curvature. The chord direction scanning of stiffened plates exhibits a larger bending curvature, indicating its greater forming capacity for large-sized single unfolding direction formation; whereas, the unfolding direction scanning of stiffened plates excels in achieving efficient integrated two-way forming. [ABSTRACT FROM AUTHOR]

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Research into the efficacy of photobiomodulation therapy (PBMT) in reducing inflammation has been ongoing for years, but standards for irradiation methodology still need to be developed. This study aimed to test whether PBMT stimulates in vitro human peripheral blood mononuclear cells (PBMCs) to synthesize pro-inflammatory cytokines, including chemokines. PBMCs were irradiated with laser radiation at two wavelengths simultaneously (λ = 808 nm in continuous emission and λ = 905 nm in pulsed emission). The laser radiation energy was dosed in one dose as a whole (5 J, 15 J, 20 J) or in a fractionated way (5 J + 15 J and 15 J + 5 J) with a frequency of 500, 1,500 and 2,000 Hz. The surface power densities were 177, 214 and 230 mW/cm2, respectively. A pro-inflammatory effect was observed at both the transcript and protein levels for IL-1β after PBMT at the energy doses 5 J and 20 J (ƒ=500 Hz) and only at the transcript level after application of PBMT at energy doses of 20 J (ƒ= 1,500; ƒ=2,000 Hz) and 5 + 15 J (ƒ=500 Hz). An increase in CCL2 and CCL3 mRNA expression was observed after PBMT at 5 + 15 J (ƒ=1,500 Hz) and 15 + 5 J (ƒ=2,000 Hz) and CCL3 concentration after application of an energy dose of 15 J (frequency of 500 Hz). Even though PBMT can induce mRNA synthesis and stimulate PBMCs to produce selected pro-inflammatory cytokines and chemokines, it is necessary to elucidate the impact of the simultaneous emission of two wavelengths on the inflammatory response mechanisms. [ABSTRACT FROM AUTHOR]

Narrowly divergent high-energy electron beam is experimentally demonstrated during the interaction of terawatt Ti:Sa laser radiation with a nitrogen gas-cluster jet at gas pressure corresponding to the boundary of the condensation region. A collimated electron beam with an energy of up to 10 MeV and a divergence of 10 mrad at a plasma concentration of ~1019 cm–3 is obtained. The use of nitrogen instead of argon or krypton significantly improves the spatial (divergence) and energy (charge and spectrum shape) properties of the generated electron beam. The formation of clusters in a supersonic jet is observed and their composition is thermodynamically analyzed. [ABSTRACT FROM AUTHOR]

In this work, (Z)-2-((E)-(2-oxoindolin-3-ylidene)hydrazono)-3-phenylthiazolidin-4-one 7 (C17H12N4O2S) as a hybrid molecule is synthesized under an easy method and analytically ascertained by 1HNMR, 13CNMR, IR, Mass, and UV–vis. spectroscopies. The optimized geometry of the synthesized hybrid molecule 7 is acquired using DFT-assisted calculations involving B3LYP equation with 6-31G(d,p) as a basis set level. At the same level, TD-DFT calculations are performed to collect the theoretical UV–vis. spectrum of the hybrid molecule 7. The nonlinear optical (NLO) properties of the hybrid molecule 7 are studied under irradiation with a cw laser beam. The nonlinear refractive index (NLRI), n2, of the hybrid molecule 7 is estimated via diffraction patterns (DPs) and Z-scan. The all optical switching is tested for the hybrid molecule 7 using two, cw, laser beams. Both static and dynamic all-optical switching are studied. [ABSTRACT FROM AUTHOR]

In this present theoretical study, an analytic formalism is developed to investigate the electrostatic lower hybrid wave by counterpropagation of two different profile laser beams in collisional plasma embedded with static magnetic field. As the counterpropagating two laser beams interact with collisional magnetized plasma, it would cause the beat wave having frequency ω = ω 1 - ω 2 and wave number k = k 1 + k 2 . The beating of two laser beams produce nonlinear ponderomotive to the plasma electrons. It would have efficient potential to couple the pre-existed electrostatic lower hybrid wave and thus driven beat wave excites the electrostatic lower hybrid. Lower hybrid wave is excited much more as the beating of two different profile laser beams polarized along the electrostatic lower hybrid wave. As the beatings of two laser beams having finite y-extent, the coupled electrostatic lower hybrid wave also possess effective y-component wave number and a component of group velocity along the static magnetic field. This leads to causes the convective losses. The spatial shape of power profile of electrostatic lower hybrid wave promises that it can be much more excited with the variation in laser beam decentered parameter, beam width parameter, Hermite polynomial mode index, laser beam transverse propagation distance, electron-neutral collision frequency and electron cyclotron frequency. One may apply this theory of electrostatic lower hybrid wave excitation in electron heating and laser high harmonic generation process. [ABSTRACT FROM AUTHOR]

This work introduces a new kind of laser beam called Laguerre-Whittaker-Gaussian beams (LWGBs) in terms of Laguerre and Whittaker functions in the source plane. Applying the integral of Huygens-Fresnel, a propagation formula of LWGBs traversing a paraxial ABCD optical system is derived. The variation of the intensity distribution of the propagated LWGBs with the beam structure parameters, such as the beam orders (m, n) and the topological charge l, is discussed with some graphical representations. The results reveal that m, n and l have a considerable impact on the beam's properties as it propagates in free space. Also, in a thin lens in a free space, it is found that the focal length affects the beam shape. In the case of the Fourier transform system, it is observed that the intensity pattern of the LWGBs is more focused with the decrease of the focal length. This research is helpful for optical communication and optical trapping because the beam studied has a zero intensity in the center. [ABSTRACT FROM AUTHOR]

We report a theoretical model for THz generation from the interaction of Gaussian laser beams with semiconductor nanoparticles suspended in argon gas in the presence of a DC magnetic field. Our investigations include two different shapes of nanoparticles [spherical (SNPs) and cylindrical (CNPs)]. The laser fields ionize nanoparticles converting them into plasma, which takes the form of spherical and cylindrical periodic nanoclusters with the electron density profile n = n 0 + n q e iqz , where q is the wave number of the density ripple and n q is the amplitude of density modulation. In our investigations, nanoparticles of AlAs and InP semiconductors are considered. Resonance condition is obtained when the laser beat frequency matches with the surface plasmon frequency of nanoparticles. We obtain resonances at two different frequencies when we apply a DC magnetic field. The resonance frequencies of THz fields shift with the nanoparticles' shape and orientation. THz field amplitude varies with material properties, spacing, size, and orientation of the nanoparticles. The applied magnetic field enhances the THz field and also helps in controlling the field profile. A THz field ∼ 0.1 GV / cm with ∼ 2 % efficiency is obtained for an optimized set of parameters for CNPs. [ABSTRACT FROM AUTHOR]

The time delay phenomenon of reflected and transmitted laser pulse under the action of s-polarized laser radiation on a supercritical plasma slab is considered. The dependence of the time delay and peak intensity of reflected and transmitted signals on the slab thickness, plasma density, and angle of laser radiation incidence is investigated. It is shown that with increasing thickness of the plasma slab, the saturation of the transmitted signal delay time (Hartman effect) does not occur due to the exponential decrease in its intensity. The tunneling speed of the laser pulse energy through the slab of supercritical plasma is calculated, and it is shown that at large angles of laser radiation incidence, it can exceed the speed of light in vacuum. [ABSTRACT FROM AUTHOR]

Aero-optical steady-distortion reduces the far-field quality of the forward-looking laser beam of an airborne turret. It has a complex relation with the viewing angle of the laser beam and the flow around the turret at different flight speeds. In this paper, the aero-optical steady-distortion, including the fixed tip/tilt and steady-lensing wavefront, for a hemisphere-on-cylinder turret with a conformal window is analyzed at different freestream Mach numbers (M a ∞ = 0.3 – 1.7) and window angles. Computational fluid dynamics and particle-based ray-tracing methods are combined to simulate the steady-state flow over the turret and its aero-optical effect. The scaling laws of the fixed tip/tilt and steady-lensing wavefront for the forward-looking laser beam are summarized under these subsonic, transonic, and supersonic flows. The results show that the scaling factor M a ∞ 2 is only applicable to the wavefront distortion caused by low-velocity flows, while the relevant scaling factors M a ∞ 2 / [ 1 + (γ + 1) M a ∞ 2 (γ + 1) / (γ − 1) ] and (γ − 1) / (2 γ) M a ∞ γ / (γ − 1) are effective across subsonic/transonic and supersonic flows. The fixed tip/tilt is discussed separately, and its scaling factor and scaling law differ from the steady-lensing wavefront. In addition, the fixed tip/tilt and steady-lensing wavefront within these flow regimes are only related to the viewing angle, not the elevation angle. [ABSTRACT FROM AUTHOR]

Quiet optical discharge in high-pressure xenon is visually stable pre-breakdown stage of optical discharge supported by pulse-periodic short-wavelength infrared laser radiation with intensity of the order of 109 W/cm2. Increasing the laser intensity leads to the transition of the quiet discharge into a pulse-periodic optical breakdown. In this study, quasi-stationary directional flows generated by both the quiet discharge and the optical breakdown are observed. The flows and their initial stages under limited number of discharge pulses are visualized by shadow imaging method using a point-like laser-plasma radiation source. It is shown that the gas streams outflow points in a quiet discharge correspond to the positions of the laser radiation intensity local maxima in the focal beam waist with astigmatism complicated by defocusing effect of thermal lens arising in the discharge zone. The pulse-periodic optical breakdown emits a turbulent gas flow toward the laser beam. The beam refraction on density gradients in the turbulent flow causes the breakdown instability from pulse to pulse. It was found that time-average absorption of laser radiation in a quiet discharge is about 3% (also in a pulse), while that in optical breakdown is 15% and higher (from 70% to 100% in a pulse). Laser beam intensity for quiet discharge at pulse repetition rate νp = 20 kHz ranges from 1.3 × 109 to 1.5 × 109 W/cm2. At intensities above 4 × 109 W/cm2 and repetition rates νp > 50–55 kHz, laser breakdowns are observed in each laser pulse with the focal ratio f/d ≤ 7. At f/d = 10.6 and νp > 28 kHz, the quiet discharge does not transit to laser breakdown due to defocusing by the thermal lens induced. [ABSTRACT FROM AUTHOR]

Determining a substance's refractive index (RI) is of great importance in a wide variety of disciplines, such as chemistry, biomedicine, engineering, and optics, to name just a few. This work utilizes critical-angle reflectometry to measure the refractive index of dentin, a biological tissue characterized by its high RI and complex structure. We fabricated a hollow semicircular prism and filled it with bromonaphthalene (1-B), allowing us to measure RIs up to 1.65. We used 5 tooth samples with exposed dentin and a laser diode beam (λ = 650 nm) incident on interface 1-B/Dentine; the reflectance curve was measured from 60° to 75°. The critical angle is determined, and dentin RI is calculated. The real part of the calculated dentine's RI coincided well with those determined by other more expensive and specialized techniques with high technical support. [ABSTRACT FROM AUTHOR]

The detection of high-flux gamma beams from laser plasma interactions is always hampered by signal pileup. In this study, a gamma threshold detector based on the bubble chamber is designed to detect high-flux gamma beams. Through simulations, it has been demonstrated that this detector can detect gamma rays with energies above 5 MeV through photonuclear reactions, even at fluences as high as 1011 photons/cm2. In addition, by setting the detection threshold at 0.1 MeV/μm, a yield of up to 10−2 bubbles per gamma interaction can be achieved. Finally, the bubble chamber in the detection of a gamma ray from the inverse Compton scattering process is also discussed. [ABSTRACT FROM AUTHOR]

Laser doping of silicon with pulsed and scanned laser beams is now well-established to obtain defect-free, doping profile tailored, and locally selectively doped regions with a high spatial resolution. Picking the correct laser parameters (pulse power, pulse shape, and scanning speed) impacts the depth and uniformity of the melted region geometry. This work performs laser doping on the surface of single crystalline silicon, using a pulsed and scanned laser profile with a Gaussian intensity distribution. A deposited boron oxide precursor layer serves as a doping source. Increasing the local inter-pulse distance x irr between subsequent pulses causes a quadratic decrease of the sheet conductance G sh of the doped surface layer. Here, we present a simple geometric model that explains all experimental findings. The quadratic dependence stems from the approximately parabolic shape of the individual melted regions directly after the laser beam has hit the Si surface. The sheet resistance depends critically on the intersection depth d ch and the distance x irr of overlap between two subsequent, neighboring pulses. The intersection depth d ch quadratically depends on the pulse distance x irr and therefore also on the scanning speed v scan of the laser. Finally, we present a simple model that reduces the complicated three dimensional, laterally inhomogeneous doping profile to an effective two-dimensional, homogeneously doped layer which varies its thickness with the scanning speed. [ABSTRACT FROM AUTHOR]

Lateral flow assay (LFA) is a handful diagnostic technology that can identify severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other common respiratory viruses in one strip, which can be tested at the point-of-care without the need for equipment or skilled personnel outside the laboratory. Although its simplicity and practicality make it an appealing solution, it remains a grand challenge to substantially enhance the colorimetric LFA sensitivity. In this work, we present a straightforward approach to enhance the sensitivity of LFA by imposing the flow constraints in nitrocellulose (NC) membranes via a number of vertical femtosecond laser micromachined microchannels which is important for prolonged specific binding interactions. Porous NC membrane surfaces were structured with different widths and densities µ-channels employing a second harmonic of the Yb:KGW femtosecond laser and sample XYZ translation over a microscope objective-focused laser beam. The influence of the microchannel parameters on the vertical wicking speed was evaluated from the video recordings. The obtained results indicated that µ-channel length, width, and density in NC membranes controllably increased the immunological reaction time between the analyte and the labeled antibody by 950%. Image analysis of the colorimetric indicators confirmed that the flow rate delaying strategy enhanced the signal sensitives by 40% compared with pristine NC LFA. [ABSTRACT FROM AUTHOR]

The use of photons to directly or indirectly drive chemical reactions has revolutionized the field of nanomaterial synthesis resulting in appearance of new sustainable laser chemistry methods for manufacturing of micro‐ and nanostructures. The incident laser radiation triggers a complex interplay between the chemical and physical processes at the interface between the solid surface and the liquid or gas environment. In such a multi‐parameter system, the precise control over the resulting nanostructures is not possible without deep understanding of both environment‐affected chemical and physical processes. The present review intends to provide detailed systematization of these processes surveying both well‐established and emerging laser technologies for production of advanced nanostructures and nanomaterials. Both gases and liquids are considered as potential reacting environments affecting the fabrication process, while subtractive and additive manufacturing methods are analyzed. Finally, the prospects and emerging applications of such technologies are discussed. [ABSTRACT FROM AUTHOR]