Focused Laser Radiation Research Articles

In situ microstructure analysis of Inconel 625 during laser powder bed fusion

Laser powder bed fusion is an additive manufacturing process that employs highly focused laser radiation for selective melting of a metal powder bed. This process entails a complex heat flow and thermal management that results in characteristic, often highly textured microstructures, which lead to mechanical anisotropy. In this study, high-energy X-ray diffraction experiments were carried out to illuminate the formation and evolution of microstructural features during LPBF. The nickel-base alloy Inconel 625 was used for in situ experiments using a custom LPBF system designed for these investigations. The diffraction patterns yielded results regarding texture, lattice defects, recrystallization, and chemical segregation. A combination of high laser power and scanning speed results in a strong preferred crystallographic orientation, while low laser power and scanning speed showed no clear texture. The observation of a constant gauge volume revealed solid-state texture changes without remelting. They were related to in situ recrystallization processes caused by the repeated laser scanning. After recrystallization, the formation and growth of segregations were deduced from an increasing diffraction peak asymmetry and confirmed by ex situ scanning transmission electron microscopy.Graphical

Formation of graphene nanostructures using laser induced vaporization of entrapped water

Facile construction of graphene nanostructures are potentially important for fundamental studies and various applications owing to its transparency and mechanical strength. Here we found that focused laser irradiation of a graphene/entrapped water/hydrophobic substrate leads to vaporization of entrapped water and consequent formation of graphene nanostructures. Graphene mechanically exfoliated on a hydrophobicized Si substrate was served as a transformable and impermeable nanocontainer in which water anisotropically and slowly diffuses from the weak edges into the van der Waals (vdW)-coupled interstitial volume between graphene and the substrate. Time-lapsed Raman mappings show that water entrapment promotes progressive lowering of the frequencies of the G and 2D bands of graphene and exhibits slower diffusion owing to vdW decoupling of substrate-induced doping and biaxial strain of graphene with hydrophobic substrate. Moreover, vaporized entrapped water promotes nanostructures by graphene sliding and bulging actions. This methodology represents viable approach to produce nanostructures from two dimensional materials.

APPLICATION OF DIFFRACTIVE OPTICAL ELEMENTS FOR OPTICAL-ELECTRONIC DIMENSIONAL INSPECTION SYSTEMS

The work is devoted to the application of diffractive optical elements in systems using the structured illumination method to the geometric parameters inspection of industrial articles. The objects of inspection in these systems are: weapon barrels, fuel pellets, fuel elements, spacer grids, ceramic ring insulators. The used diffractive optical elements are computer-synthesized holograms that focus laser radiation into geometric shapes, the configuration of which is optimally combined with the inspected objects shape.

Laser paintbrush as a tool for modern art

Light is critical for art. It allows us to see color, and can itself be a tool for creating unique pieces of art and design. Here we demonstrate that a laser can be a multifunctional and effective tool for the creation of masterpieces, analogous to the process of an artist creating a canvas with classical paints and brushes. We investigate the interaction between focused laser irradiation and metallic surfaces and analyze the optical effects in thin oxide films for three main artistic operations: color making, multiple color changes, and erasing managed by a nanosecond laser. These processes are possible upon heating the material above the evaporation point and are proved to be dependent on the cooling rate, according to both experimental and theoretical results. Such an interference-based laser paintbrush could find applications in modern art and design.

Features of the process of laser welding of cast iron with steel

The article presents the results of research on laser welding of cast iron with steel on a robotic laser technological complex. A system of technical vision for precision focusing of laser radiation on the joint of welded elements is presented, which provides control of the movement of the laser beam along the welded joint and adjustment of the radiation power, depending on the temperature of the joint. The welding process is carried out in a protective atmosphere of inert gases. Rough guidance of the beam is carried out by the robotic complex until the point “start of welding” falls into the field of view of the technical vision system, which is built into the process head. Precision positioning of the beam focus on the seam is provided by turning the focusing lens to a certain angle by a piezo actuator. The results of metallographic studies of the welded seam of cast iron and steel are presented.

Effects of different wavelengths of invasive laser acupuncture on chronic non-specific low back pain: a study protocol for a pilot randomized controlled trial

BackgroundChronic non-specific low back pain (CLBP) is a common musculoskeletal disorder for which patients seek complementary and alternative medical treatments, including laser acupuncture (LA). Invasive LA (ILA) involves the simultaneous application of invasive acupuncture treatment at acupoints and focused laser irradiation. The efficacy of ILA for CLBP remains controversial owing to the insufficient clinical trial data. We intend to obtain basic data regarding the efficacy and safety of ILA for CLBP by comparing the effects of different wavelengths of ILA on CLBP.MethodsThis will be a prospective, patient-blinded, parallel-arm, single-center (DongShin University Gwangju Korean Medicine Hospital, Republic of Korea), pilot randomized controlled clinical trial. Forty-five participants with CLBP will be randomized in equal numbers into the control, 650-nm ILA (650 ILA), or 830-nm ILA (830 ILA) group. The control group will receive sham ILA for 10 min and real electroacupuncture (EA) for 10 min. The 650 and 830 ILA groups will receive real ILA (i.e., 650 ILA group, 650-nm wavelength; 830 ILA group, 830-nm wavelength) for 10 min and real EA for 10 min once/day, twice a week for 4 weeks, at bilateral Shenshu (BL23), Qihaishu (BL24), Dachangshu (BL25), and Huantiao (GB30). The primary outcome will be an improvement in pain intensity assessed using the visual analog scale. Scores in the Korean version of the Oswestry Disability Index and the European Quality of Life Five Dimension Five Level scale will be recorded as secondary outcome measures. All scores will be recorded at baseline (before intervention), 4 weeks after the first intervention (at the end of the intervention), and 4 weeks after completion of the intervention.DiscussionThe study is expected to provide preliminary evidence regarding the efficacy, safety, and usefulness of ILA for the treatment of CLBP.Trial registrationThis trial was registered with the Clinical Research Information Service (registration No. KCT0004610; http://cris.nih.go.kr). Registered on 7 January 2020.

Investigation of coherence properties of white light emission of tungsten lamp additionally excited with laser radiation

The coherence properties of white light emission of a tungsten incandescent lamp additionally excited with laser radiation are investigated. The degree of spatial coherence is determined from measurements of the contrast of interference fringe patterns obtained for a tungsten bulb as the light source. It is demonstrated that the degree of spatial coherence of an incandescent lamp is increased by additional excitation of the filament with focused laser radiation. Furthermore, the degree of spatial coherence can be adjusted by selecting the voltage applied to the filament. Such light sources can find applications in imaging techniques where precise control of spatial coherence of illumination is required.

The Role of Thermal Accumulation on the Fabrication of Diffraction Gratings in Ophthalmic PHEMA by Ultrashort Laser Direct Writing.

The fabrication of diffraction gratings by ultrashort direct laser writing in poly-hydroxyethyl-methacrylate (PHEMA) polymers used as soft contact lenses is reported. Diffraction gratings were inscribed by focusing laser radiation 100 µm underneath the surface of the samples. Low- and high-repetition rate Ti:sapphire lasers with 120 fs pulsewidth working at 1 kHz and 80 MHz respectively were used to assess the role of thermal accumulation on microstructural and optical characteristics. Periodic patterns were produced for different values of repetition rate, pulse energy, laser wavelength, distance between tracks, and scanning speed. Compositional and structural modifications of the processed areas were studied by micro-Raman spectroscopy showing that under certain parameters, thermal accumulation may result in local densification. Far-field diffraction patterns were recorded for the produced gratings to assess the refractive index change induced in the processed areas.

Особенности применения лазерного коаксиального плавления порошковых материалов для создания объектов из сплавов на основе меди

Among the methods of additive technologies, coaxial laser melting, i.e. direct metal deposition (DMD), is quite widespread. Essentially, this process is about creating objects by sequentially deposing layers of powder and melting them due to their simultaneous supply through a nozzle with focusing of laser radiation into the processing zone. Various powders are used as materials for this technology, the powders being selected depending on the tasks and final characteristics. One of the promising directions for implementation is the creation of complex structures from copper alloys for aircraft construction. Despite the fairly widespread use of this technology in relation to copper alloys, in particular bronzes, there is a small amount of data and research for this technology. The purpose of this study was to understand the process of forming the materials when grown by the DMD method. For this purpose, the fusion of bronzes with a steel substrate was investigated; special aspects were revealed, which made it possible to pose the second task - the study of fusion of bronzes with a copper substrate. As a result, the microstructure of the samples was considered and their micro-hardness was measured.

The photonic nanojets formation by two-dimensional microprisms

Using the finite difference method implemented in the COMSOL Multiphysics software package, the focusing of laser radiation by dielectric prisms with a triangular profile was numerically investigated. It was shown that two-dimensional triangular prisms make it possible to focus light in free space into spots with dimensions smaller than the scalar diffraction limit. In particular, a silica glass prism with a base width of 60 μm and a height of 28.5 μm forms a photonic nanojet with a maximum intensity of 6 times the intensity of the incident radiation and a width of FWHM=0.38λ. A prism from barium titanate with a base width of 60 μm and a height of 20 μm allows to obtain a photonic nanojet with the same width (0.38λ) and a maximum intensity 5 times the intensity of the incident radiation. The size of the focal spot can be reduced further if the height of the prism is selected so that the maximum intensity is located inside the material of the prism. For example, a barium titanate prism with a height of 21 μm and a base width of 60 μm forms a focal spot with a width of FWHM=0.25λ.

Adaptive system for wavefront correction of the PEARL laser facility

The results of the operation of a wavefront correction system based on a deformable bimorph mirror of the PEARL subpetawatt laser facility are presented. An improvement in the quality of focusing of laser radiation, which led to an increase in the Strehl ratio from 0.3 to 0.6, is demonstrated. The features of the compensation for phase distortions of the wavefront in the case of a low pulse repetition rate, as well as the correct allowance for the noise of the CCD camera when calculating the Strehl ratio are investigated.

Revealing nucleoplasm mechanics by optical trapping and Brownian motion of nucleolus within mouse GV-oocytes in vivo

Optical trapping of nucleoli within nucleoplasm of living oocytes as unique model system provides non-invasive technique for investigation of nuclear environment. We employed methods of active and passive rheology to characterize rheological properties of the nucleoplasm of GV-oocytes (germinal vesicle stage) with main types of chromatin distribution in the nucleus (NSN, SN). By using of single beam optical trap, formed by a tightly focused laser radiation at 790 nm wavelength, we performed subsequent stress-relaxation tests series of nucleoli in various directions and with different amplitudes. Nucleolus of the oocyte was employed as a microprobe due to its large size and spherical shape. The characteristic nucleolus relaxation times were obtained for two types of chromatin distribution, which can subsequently be used to evaluate the viscoelastic properties of the nuclear material within oocytes with different physiological states. Motion activity of nucleoli was also extracted to evaluate local forces, acting within nucleolar environment and facilitating chromatin redistribution.

A Method for Recording the Bioelectrical Activity of Neural Axons upon Stimulation with Short Pulses of Infrared Laser Radiation.

The aim of the study was to develop a method for long-term non-invasive recording of the bioelectrical activity induced in isolated neuronal axons irradiated with short infrared (IR) pulses and to study the effect of radiation on the occurrence of action potentials in axons of a neuron culture in vitro.Materials and Methods.Hippocampal cells of mouse embryos (E18) were cultured in microfluidic chips made of polydimethylsiloxane and containing microchannels for axonal growth at a distance of up to 800 μm. We studied the electrophysiological activity of a neuronal culture induced by pulses of focused laser radiation in the IR range (1907 and 2095 nm). The electrophysiological activity of the neuronal culture was recorded using a multichannel recording system (Multi Channel Systems, Germany).Results.The developed microfluidic chip and the optical stimulation system combined with the multichannel registration system made it possible to non-invasively record the action potentials caused by pulsed IR radiation in isolated neuronal axons in vitro. The propagation of action potentials in axons was detected using extracellular microelectrodes when the cells were irradiated with a laser at a wavelength of 1907 nm with a radiation power of 0.2–0.5 W for pulses with a duration of 6 ms and 0.5 W for pulses with a duration of 10 ms. It was shown that the radiation power positively correlated with the occurrence rate of axonal response. Moreover, the probability of a response evoked by optical stimulation increased at short optical pulses. In addition, we found that more responses could be evoked by irradiating the neuronal cell culture itself rather than the axon-containing microchannels.Conclusion.The developed method makes it possible to isolate the axons growing from cultured neurons into a microfluidic chip, stimulate the neurons with infrared radiation, and non-invasively record the axonal spiking. The proposed approach allowed us to study the characteristics of neuronal responses in cell cultures over a long (weeks) period of time. The method can be used both in fundamental research into the brain signaling system and in the development of a non-invasive neuro-interface.

Laser Formation of Holes in Nonmetallic Substrates

The use of a pulse picosecond laser with a wavelength of 532 nm and frequency of 15 Hz in the formation of holes with diameters up to 0.1 mm in nonmetallic substrates (silicon, ceramics, etc.) was proposed. It was found by modeling in MathCAD and COMSOL Multiphysics that the half-angle value of the light cone aperture that depends on the focusing of laser radiation exerts a significant effect on the depth and diameter of holes in laser processing. The influence of the regimes of laser processing employing nanosecond and picosecond lasers with wavelengths of 1064 and 532 nm, respectively, on the conicity and time of formation of holes in silicon substrates was investigated. The preliminary heating of the substrate to 170–200°С reduces the time of formation of the holes by 20%.

Tannic acid-functionalized boron nitride nanosheets for theranostics

Here, we report a tannic acid-Fe3+ coordination complex coating that confers magnetic resonance imaging (MRI) theranostic properties to inert nanomaterials. Boron nitride nanosheets (BNS), which lack magnetic field and light responsiveness, were used as a model nonfunctional nanomaterial. Among various catechol derivatives tested (i.e., dopamine, 3,4-dihydroxyphenylacetic acid, gallic acid, and tannic acid), a coating of tannic acid-Fe3+ coordination complex provided the highest magnetic field relaxivity and near infrared (NIR) laser light responsiveness. An in vitro study showed that KB tumor cells treated with tannic acid-Fe3+ coordination complex adsorbed on BNS (TA-Fe/BNS) exhibited higher T1-weighted magnetic resonance contrast compared with plain BNS, and BNS coated with tannic acid or Fe alone. NIR irradiation at 808 nm caused a significant increase in KB tumor cell death after treatment with TA-Fe/BNS compared with other treatments. In vivo MRI imaging revealed tumor accumulation of intravenously administered TA-Fe/BNS. Guided by MRI information, application of focused laser irradiation onto tumor tissues resulted in complete tumor ablation. These results support the potential of TA-Fe/BNS for MRI theranostics. Moreover, this study suggests the wide applicability of TA-Fe noncovalent coating as biocompatible and facile tool for converting nonfunctional early-generation nanomaterials into functional new nanomaterials, opening new opportunities for their use in translational biomedical applications such as MRI theranostics.

Microfocusing sapphire capillary needle for laser surgery and therapy: Fabrication and characterization.

A sapphire shaped capillary needle designed for collimating and focusing of laser radiation was proposed and fabricated by the edge-defined film-fed growth technique. It features an as-grown surface quality, high transparency for visible and near-infrared radiation, high thermal and chemical resistance and the complex shape of the tip, which protects silica fibers. The needle's geometrical parameters can be adjusted for use in various situations, such as type of tissue, modality of therapy and treatment protocol. The focusing effect was demonstrated numerically and observed experimentally during coagulation of the ex vivo porcine liver samples. This needle in combination with 0.22NA optical fiber allows intensive and uniform coagulation of 150 mm3 volume interstitially and 30 mm3 superficially by laser exposure with 280 J without tissue carbonization and fiber damaging along with delicate treatment of small areas. The demonstrated results reveal the perspectives of the proposed sapphire microfocusing needle for laser surgery and therapy.

The combined use of adaptive optics and nonlinear optical wavefront reversal techniques to compensate for turbulent distortions when focusing laser radiation on distant objects

Approaches to constructing a mock-up of a system for focusing laser radiation on distant objects using both adaptive optics elements and nonlinear-optical wavefront reversal methods providing compensation for turbulent distortions are considered. Numerical calculations were preliminarily performed, in which the split-step method was used as a numerical method for solving a second-order partial differential wave equation for the complex amplitude of the wave field of a laser beam. This method, combined with methods of spectral-phase Fourier transforms and statistical tests, is the most effective way to obtain reliable quantitative results for solving engineering problems of atmospheric wave optics. Quantitative data are obtained on the effect of turbulent atmospheric distortions along propagation paths on the main parameters of coherent laser beams – focusing, effective average radius, and the proportion of the beam energy in its diffraction spot. The preliminary results obtained of the system mock-up performance confirm the conclusions of the theory.

Quantitative Analysis of Hydrogen in High-Hydrogen-Content Material of Magnesium Hydride via Laser-Induced Breakdown Spectroscopy.

An analytical approach that can rapidly determine a wide range of hydrogen concentration in solid-state materials has been recently demanded to contribute to the hydrogen economy. This study presents a method for estimating hydrogen concentrations ranging from 0.2 to 7.6 mass % via laser-induced breakdown spectroscopy (LIBS) in a few seconds, with an improvement in the upper limit of determination (7.6 mass %) by approximately 1.3 times compared with a previous work (5.7 mass %). This extension of the determinable concentration range was achieved by measuring the emission intensity at 656.28 nm from the sample in a helium atmosphere at 3000 Pa under focused laser irradiation and by reducing the water residues in both the sample and gas line of the LIBS system. The as-determined hydrogen concentrations in magnesium hydride (MgH2) samples agreed well with those estimated through inert gas fusion/gas chromatography. The calibration curve for LIBS analysis was acquired by measuring the emission intensity at 656.28 nm of standard Mg/MgH2 mixtures containing various hydrogen concentrations (0, 0.1, 0.2, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, and 7.6 mass %). Results indicated that the proposed LIBS-based method is applicable to the rapid quantitative analysis of hydrogen in hydrogen-containing material of MgH2.

MASK RECORDING TECHNIQUE OF ON MULTILAYERED COATINGS (part 2)

The experimental determination of the reflection coefficients in the visible region of the spectrum of chromium oxide films unexposed and exposed to laser radiation was performed. The reflection coefficients were measured using a Linza - 150 spectrophotometer (operating spectrum range from 380 to 1700 nm). The obtained characteristic values of the reflection coefficients of samples of chromium oxide films at different wavelengths are presented in the table and in the form of graphs. It was found that the reflectance of the chromium oxide film before exposure to laser radiation monotonically decreases with increasing wavelength from 380 to 450 nm, with a further increase in wavelength to 630 nm, the reflectance increases monotonically. This work is part of the development of a technique for recording masks by focused laser radiation on multilayer absorbing coatings.

Distributed Focusing of Laser Radiation and Applications Possibility

A new type of focusing is reported. For the first time, the lenses necessary to obtain the distributed focusing are described. The approximate calculation shows that this type of focusing can be useful in surgery, industry and information technology. There is only one type of distributed focusing at this moment, that is Bessel beam. In this type of beams, energy flux, excurrenting out of axicon, is distributed by a line segment. Power distribution by the line segment can be changed by varying the intensity profile of the incoming beam. Another way is presented in the paper. There are two types of laser scalpels (contact and non-contact ones), but this type of focusing can be used as a base for creating new types of laser scalpels with fundamentally new characteristics. Also this focusing can be applied to creation of more efficient laser cutters.