Energy Density Of Laser Beam Research Articles

Effect of combined radiation processing on parameters of Si-based MOS transistors

ABSTRACTThe variation of parameters of Si-based MOS-transistors affected by combined infrared and X- ray photons processing were presented. It was found that X-ray irradiated transistor under incoherent infrared radiation is characterized by lowering of radiation sensitivity. As positive charge and its radiation-induced rate of generation in undergate SiO2 insulator decreases, we observe a reduction of both ΔUNo and voltage threshold Uth transistor components. Under pulsed laser processing (λ = 1.06 µm, τ = 10−3s) of the X-rays irradiated transistor the energy density of laser beam corresponding to the minimum threshold voltage was established. It was shown that the combined treatment can be effectively used to control the transistor parameters. The model describing the radiation changes of parameters in Si-SiO2 structure was proposed. The effect of Na+, K+ and H+ ions in undergate insulator on variation of charge state and interface reconstruction under laser irradiation were predicted by proposed model.

The AlSi10Mg samples produced by selective laser melting: single track, densification, microstructure and mechanical behavior

This densification behavior and attendant microstructural characteristics of the selective laser melting (SLM) processed AlSi10Mg alloy affected by the processing parameters were systematically investigated. The samples with a single track were produced by SLM to study the influences of laser power and scanning speed on the surface morphologies of scan tracks. Additionally, the bulk samples were produced to investigate the influence of the laser power, scanning speed, and hatch spacing on the densification level and the resultant microstructure. The experimental results showed that the level of porosity of the SLM-processed samples was significantly governed by energy density of laser beam and the hatch spacing. The tensile properties of SLM-processed samples and the attendant fracture surface can be enhanced by decreasing the level of porosity. The microstructure of SLM-processed samples consists of supersaturated Al-rich cellular structure along with eutectic Al/Si situated at the cellular boundaries. The Si content in the cellular boundaries increases with increasing the laser power and decreasing the scanning speed. The hardness of SLM-processed samples was significantly improved by this fine microstructure compared with the cast samples. Moreover, the hardness of SLM-processed samples at overlaps was lower than the hardness observed at track cores.

LIPSS formed on the sidewalls of microholes in stainless steel trepanned by a circularly polarized femtosecond laser

In order to take advantage of microhole fluidynamics, laser-induced periodic surface structures (LIPSS, ripples) orientation should offer the lowest angle γ as possible with respect to hole axis. Investigations have been performed to explore the morphology of LIPSS formed on the sidewalls of microholes by circularly polarized femtosecond laser trepanning. The period of LIPSS on average was smaller than laser wavelength. The energy density of laser beam generally affected the processing effect. Experiments showed that the angle of the LIPSS decreases with increasing single pulse energy. However, increasing trepanning speed led to a decreasing in LIPSS angle.

Post Processing and Biological Evaluation of the Titanium Scaffolds for Bone Tissue Engineering.

Nowadays, post-surgical or post-accidental bone loss can be substituted by custom-made scaffolds fabricated by additive manufacturing (AM) methods from metallic powders. However, the partially melted powder particles must be removed in a post-process chemical treatment. The aim of this study was to investigate the effect of the chemical polishing with various acid baths on novel scaffolds’ morphology, porosity and mechanical properties. In the first stage, Magics software (Materialise NV, Leuven, Belgium) was used to design a porous scaffolds with pore size equal to (A) 200 µm, (B) 500 µm and (C) 200 + 500 µm, and diamond cell structure. The scaffolds were fabricated from commercially pure titanium powder (CP Ti) using a SLM50 3D printing machine (Realizer GmbH, Borchen, Germany). The selective laser melting (SLM) process was optimized and the laser beam energy density in range of 91–151 J/mm3 was applied to receive 3D structures with fully dense struts. To remove not fully melted titanium particles the scaffolds were chemically polished using various HF and HF-HNO3 acid solutions. Based on scaffolds mass loss and scanning electron (SEM) observations, baths which provided most uniform surface cleaning were proposed for each porosity. The pore and strut size after chemical treatments was calculated based on the micro-computed tomography (µ-CT) and SEM images. The mechanical tests showed that the treated scaffolds had Young’s modulus close to that of compact bone. Additionally, the effect of pore size of chemically polished scaffolds on cell retention, proliferation and differentiation was studied using human mesenchymal stem cells. Small pores yielded higher cell retention within the scaffolds, which then affected their growth. This shows that in vitro cell performance can be controlled to certain extent by varying pore sizes.

The effect of process parameters on rhenium diboride films deposited by PLD

Rhenium diboride (ReB2) thin films have been deposited by a nanosecond pulsed laser deposition method on Si (100) substrate heated to 570°C. The coatings were formed in the ablation process of SPS sintered ReB2 target. The effect of laser wavelength, energy density and postannealing on the films' properties was studied. Investigated wavelengths were 355 and 1064nm of Nd:YAG nanosecond laser. Laser beam energy density varied from 2.1 to 6.1Jcm−2 and from 4.1 to 9.4Jcm−2 at 355 and 1064nm, respectively. Layer thickness was of the order of several hundred nanometres. Deposition efficiency increases with an energy density in quasi linear way and strongly grows for shorter wavelength. The layers consist of two characteristic microstructures: a smooth basis and stick debris (typical diameters of several hundred nanometres). Lower energy density of laser beam and longer wavelength favour dominance of smooth basis and minimization of debris. The XRD analysis of all samples indicate the crystalline ReB2 with preferred (002) orientation and fine grain size of about 20nm. Shorter wavelength and higher energy density foster stronger (002) orientation. Moreover, an annealing right after the deposition (25min in 350°C) causes minimization of degree of orientation and decrease of hardness. The Vickers hardness of ReB2 films is at about 60GPa and is reduced to about 40GPa after the annealing process. Deposition efficiency and physical and chemical structures of layers produced under variety of conditions were studied and compared.

A new experimental setup for high-throughput controlled non-photochemical laser-induced nucleation: application to glycine crystallization

Non-photochemical laser-induced nucleation (NPLIN) has been a growing field of study since 1996, and more than 40 compounds including organics, inorganics and proteins have now been probed under various conditions (solvents, laser types, laser beams etc.). The potential advantages of using this technique are significant, in particular polymorphic control. To realize these benefits, the objective is a carefully designed experimental setup and highly controlled parameters, for example temperature and energy density, in order to reduce the uncertainty regarding the origin of nucleation. In this paper, a new experimental setup designed to study NPLIN is reported. After a full technical description of the present setup, the different functionalities of this device will be illustrated through results on glycine. Glycine crystals obtained through NPLIN nucleate at the meniscus and exhibit different morphologies. The nucleation efficiency, as a function of the supersaturation of the solution used and the laser beam energy density, has also been established for a large number of samples, with all other parameters held constant.

Properties of thermoelectric Ce0.09Fe0.67Co3.33Sb12/FeSb2Te multi-layered structures prepared by laser ablation

Multi-layered Ce0.09Fe0.67Co3.33Sb12/FeSb2.1Te structures composed of thin equidistant layers were prepared by Pulsed Laser Deposition on fused silica quartz glass substrates. The structures were prepared at different substrate temperatures (230 °C or 250 °C) applying the laser beam energy density of 3 Jcm−2. In the contribution we present some thermoelectric properties such as the in-plane electrical conductivity, the Seebeck coefficient and the power factor for the multi-layered structures in the temperature range from 300 K to 500 K. Comparison of multi-layered structure's thermoelectric properties with single thin Ce0.09Fe0.67Co3.33Sb12 and FeSb2.1Te layers is given. A cross sectional picture of the multi-layered structure made by Scanning Electron Microscope is presented for the thicker multi-layered structure.

Properties of thermoelectric Ce0.09Fe0.67Co3.33Sb12/FeSb2Te multi-layered structures prepared by laser ablation

Multi-layered Ce0.09Fe0.67Co3.33Sb12/FeSb2.1Te structures composed of thin equidistant layers of different thickness were prepared by pulsed laser deposition on fused silica quartz glass substrates. The structures were prepared at substrate temperatures (230°C or 250°C) applying the same laser beam energy density (3Jcm−2). In the contribution we present some thermoelectric properties such as in-plane electrical conductivity, the Seebeck coefficient and the power factor of the multi-layered structures in the temperature range from 300K to 500K. Comparison of multi-layered structure's thermoelectric properties with single thin Ce0.09Fe0.67Co3.33Sb12 and FeSb2.1Te layers is given. X-ray diffraction patterns are shown. A cross-sectional picture of the multi-layered structure made by scanning electron microscope is given for the thicker multi-layered structure.

Nanostructuring of single-crystal silicon carbide by picosecond UV laser radiation

Surface nanostructures are produced on single-crystal 4H-SiC by laser ablation in water using a Nd : YAG laser ( wavelength, pulse duration) as a radiation source. The morphology of the nanostructured surface and the nanostructure size distribution are examined in relation to the energy density of the incident laser beam. The potential of the described process for improving the luminosity of light-emitting diodes on silicon carbide substrates is discussed.

Thermoelectric Properties of Ce0.09Fe0.67Co3.33Sb12/FeSb2Te Multi-Layered Structures

Thermoelectric properties of Ce0.09Fe0.67Co3.33Sb12/FeSb2.1Te multi-layered structures with period of 5 nm were studied in temperature ranging from 300 K to 500 K. Structures were prepared by Pulsed Laser Deposition (PLD) on fused sili- ca quartz glass substrates at the substrate temperature during the deposition Ts = 230°C and Ts = 250°C with the laser beam energy density Ds = 3 Jcm-2. In the contribution temperature dependencies of the in-plane electrical conductivity, the Seebeck coefficient and the resultant power factor together with room temperature value of thermoelectric figure of merit are presented.

Narrow-band tunable laser system for a lidar facility

A unique ultraviolet laser system has been developed for a lidar intended to detect nitrogen oxide molecules in the atmosphere. The electric-discharge KrF laser system is capable of producing a highly coherent laser beam with practically the same energy over a spectral range of 247.5–249.5 nm. At the edge of the amplification band in the range 247.5–247.8 nm, the system produces a beam of energy 0.3 J, pulse duration 16 ns, and spectral line width 2 pm. Atmospheric sounding by using this beam with an energy density of 200 mJ/cm2 in the scattered signal has detected noise in the 226 and 236 nm bands whose intensity increases the laser beam pulse repetition rate and energy density.

Mitigation of laser damage growth in fused silica by using a non-evaporative technique

A non-evaporative technique is used to mitigate damage sites with lateral sizes in a range from 50 μm to 400 μm and depths smaller than 100 μm. The influence of the pulse frequency of a CO2 laser on the mitigation effect is studied. It is found that a more symmetrical and smooth mitigation crater can be obtained by increasing the laser pulse frequency form 0.1 to 20 kHz. Furthermore, the sizes of laser-affected and distorted zones decrease with the increase of the laser pulse frequency, leading to less degradation of the wave-front quality of the conditioned sample. The energy density of the CO2 laser beam is introduced for selecting the mitigation parameters. The damage sites can be successfully mitigated by increasing the energy density in a ramped way. Finally, the laser-induced damage threshold (LIDT) of the mitigated site is tested using 355 nm laser beam with a small spot (0.23 mm2) and a large spot (3.14 mm2), separately. It is shown that the non-evaporative mitigation technique is a successful method to stop damage re-initiation since the average LIDTs of mitigated sites tested with small or large laser spots are higher than that of pristine material.

Absolute atomic chlorine densities in a Cl2 inductively coupled plasma determined by two-photon laser-induced fluorescence with a new calibration method

Absolute densities of chlorine atoms were determined in an inductively coupled plasma in pure chlorine gas as a function of gas pressure and RF power by two-photon laser-induced fluorescence. A new technique is proposed to put the relative two-photon laser-induced fluorescence (TALIF) measurements on an absolute scale, based on photolysis of Cl2 gas (without plasma) with a tripled Nd : YAG laser at 355 nm. Because the dissociation cross-section and photo-dissociation laser beam energy density are well known, the absolute densities can be determined with high accuracy. We find that the ratio of the Cl atom density normalized to the Cl2 gas density without plasma at the reactor centre increases with RF power and decreases with gas pressure, reaching 20% at 2 mTorr 500 WRF.

Eye safety for scanning laser projection systems

In the growing field of pico-projectors, laser-based scanning systems may be advantageous over DLP- or LCoS-based imagers due to their potential for miniaturization, enhanced optical efficiency and cost reduction. The high energy density of a combined laser beam can, however, be hazardous to the human eye. Laser projection systems must therefore be identified with the laser class, depending on their maximum optical output power. This power limits the brightness of the displayed image, which is of particular interest for mobile applications. Various approaches to classifying laser devices by their wavelength and output power are described within the standards for laser safety. It is found that actual safety regulations cannot be directly applied to scanning systems. A detailed analysis of the optical conditions in terms of a two-dimensional extended light source is appropriate for the consideration of laser scanner devices. In this article, alternative ways of applying laser standards for scanning systems are discussed. The dependencies of maximum luminous flux from scanning system parameters are reviewed. It is shown that the evaluation of retinal light exposure in terms of existing laser regulations leads to an overestimation of the hazardous potential. Advanced investigations are proposed to support the definition of suitable criteria for the classification of laser scanning projectors.

Single-Pass Laser-Gma Hybrid Welding of 13.5 mm thick duplex stainless steel

Single-pass solid-state laser welding of plates in the thickness range of 10 to 20 mm became possible with the invention of the fibre laser. This new technique provides excellent beam quality at powers as high as 20 kW or more, and has proved applicable in several industrial applications. By replacing conventional methods with the fibre laser, it is possible to avoid multiple-pass welding that requires time-consuming bevelling. The high energy density of the fibre laser beam also reduces the heat input and consequently the distortion. However, the rapid solidification and cooling associated with laser welding can cause imbalance of the microstructure of duplex stainless steel weldments, where excessively high ferrite contents may reduce the corrosion resistance and the ductility of the material. The solution is normally to add nickel-based filler wire and to increase the heat input. By using a hybrid welding process where the laser beam and the gas metal arc (GMA) process act in a common process zone, filler metal can be added to the molten pool at higher heat input and at the same time, higher welding speed and deeper penetration can be achieved. In this work, 13.5 mm thick 2205 (EN 1.4462, UNS S31803) was fibre laser-GMA hybrid welded in a single-pass using 14 kW of laser power and ISO 22 9 3 N L as filler wire for the GMA process. The resulting welds were free from defects, with smooth surfaces and full penetration. The investigation examines the weld metal microstructure and the effect on corrosion resistance and mechanical properties. The option to add nickel foil, when hybrid welding, was also investigated, as comparison, and the effect on austenite formation was evaluated.

Effect of laser beam energy density on the structural and electrical properties of TiO2-doped Bi5Nb3O15 thin film grown by pulsed laser deposition

With the addition of TiO2, the dielectric constant (εr) of a Bi5Nb3O15(B5N3) film was slightly increased and the leakage current decreased, probably due to the increased dipole moment and the decreased number of free electrons in the film, respectively. The energy density of the laser beam considerably influenced the structure and electrical properties of the 1.0 mol% TiO2-doped B5N3 (TBN) films. At low beam energy densities (⩽2.0 J cm−2), Bi3NbO7 and Bi8Nb18O57 phases with a porous microstructure were formed and a poor interface was also formed between the film and the electrode. However, for the TBN film grown at 200 °C at a high beam energy density of 4.0 J cm−2, a dense Bi3NbO7 phase was formed with a sharp interface. The εr value of this TBN film was very high, approximately 115, with a low leakage current density of 1.4 × 10−8 A cm−2 at 0.5 MV cm−1 and a high breakdown field of 0.55 MV cm−1. This improvement in the εr value and the electrical properties was explained by the formation of a dense Bi3NbO7 phase with a (1 1 1) preferred orientation, Ti doping and a sharp interface, indicating that the TBN film is a good candidate material for embedded capacitors.

Properties of thin N-type Yb0.14Co4Sb12 and P-type Ce0.09Fe0.67Co3.33Sb12 skutterudite layers prepared by laser ablation

The properties of thin thermoelectric layers (about 60 nm in thickness) prepared by pulsed laser deposition are presented. Hot pressed targets were made from “middle” temperature range thermoelectric bulk materials with the potential high figure of merit ZT. P-type and N-type layers were prepared from Yb0.19Co4Sb12 and Ce0.1Fe0.7Co3.3Sb12 targets, respectively. The thin films were deposited on quartz glass substrates using KrF excimer laser. The individual layers were prepared by applying different laser beam energy densities (2 or 3 J cm−2) at several substrate temperatures (200, 250, or 300 °C). Crystallinity and composition of the layers were examined by x-ray diffraction and wavelength dispersive analysis, respectively. Homogeneity of Yb across a surface of the Yb filled film was explored by secondary ion mass spectrometry. The thermoelectric properties, the Seebeck coefficient, the electrical resistivity, and the power factor, for the best prepared P and N layer are presented in the temperature range from 300 to 500 K.

Microwave characterization of nanostructured ferroelectricBa0.6Sr0.4TiO3 thin films fabricated by pulsed laser deposition

A series of nanostructured ferroelectric thin films of barium strontium titanate werefabricated using a pulsed laser deposition system with real-time in situ processcontrol. Pulsed laser deposition parameters were controlled during the growth ofnanostructured thin films for use in the development of high frequency tunable microwavedevices. The thin films were all grown at the same substrate temperature and laserbeam energy density, but the chamber oxygen partial pressure (COPP) was variedsystematically from 19 mTorr through 1000 Torr. Structural and electromagneticcharacterization was performed using atomic force microscopy and evanescent microwavemicroscopy, respectively. Atomic force microscopy showed a linear increase in grain sizewith increases in the ambient oxygen pressure from 38 to 150 mTorr and from300 mTorr to 1000 Torr. The correlation of the microwave properties with the epitaxialfilm microstructure can be attributed to stresses and polarizability in the film.Microwave characterization showed that a COPP of 75 mTorr yielded the mostdesirable film in terms of tunability and loss tangent over a wide frequency range.

Electrical and dielectrical properties of tantalum oxide films grown by Nd:YAG laser assisted oxidation

Tantalum pentoxide (Ta 2O 5) thin films (20 to 44 nm) have been grown by 1064 nm Nd:YAG laser oxidation of Ta deposited films with various thickness on Si. Fourier Transform Infrared (FTIR) spectrum, thickness distribution, dielectric and electrical properties of laser grown oxide layers have been studied. The effect of the sputtered Ta film thickness, laser beam energy density and the substrate temperature on the final Ta 2O 5 film structure has been determined. It is shown that the oxide layers obtained for the laser beam energy density in the range from 3.26 to 3.31 J/cm 2 and the substrate temperature around 350 °C have superior properties. FTIR measurement demonstrates that the Ta 2O 5 layers are obtained with the laser assisted oxidation technique. Metal Oxide Semiconductor capacitors fabricated on the grown oxide layers exhibits typical Capacitance–Voltage, Conductance–Voltage and Current–Voltage characteristics. However, the density of oxide charges is found to be slightly higher than the typical values of thermally grown oxides. The conduction mechanism studied by Current–Voltage measurements of the capacitors indicated that the current flow through the oxide layer is modified Poole–Frenkel type. It is concluded that the Ta 2O 5 films formed by the technique of Nd:YAG laser-enhanced oxidation at relatively low substrate temperatures are potentially useful for device applications and their properties can be further improved by post oxidation annealing processes.

Thin layers of bovine serum albumin by matrix assisted pulsed laser evaporation

Thin films of bovine serum albumin were prepared by cryogenic matrix assisted pulsed laser evaporation technique under various deposition conditions. Energy density of laser beam changed in the range 0.1–0.5 J cm −2. Films were deposited in vacuum or in nitrogen ambient. Targets were prepared from bovine serum albumin solution in phosphate buffered physiological saline and with an addition of UV absorbers as dimethylsulphoxide, phthalic acid, or adenine. Polyethylene and silicon (1 1 1) were used as substrates. Film properties were studied with atomic force microscopy and Fourier transform infrared spectroscopy attenuated total reflection. The deposition changed native conformation of albumin, resulting in the formation of water-insoluble aggregates. Addition of laser light absorbers in target solutions did not prevent the damage of albumin structure.