Effects Of Laser Pulse Energy Research Articles

Crystallization of Germanium-SiO2 composite films via nanosecond laser pulse irradiation

Germanium (Ge)-SiO2 composite films fabricated by using radio frequency magnetron co-sputtering were subjected to nanosecond (ns) laser pulse irradiation. The intense laser irradiation effects on as deposited composite films lead to the modification and the formation of Ge nanocrystals (NCs) embedded in SiO2. The as-deposited and laser treated samples have been characterized with X-ray diffraction (XRD) and micro-Raman spectroscopy to understand the formation of Ge NCs due to laser irradiation. The respective Ge NCs related peaks in XRD pattern as well as the Ge-Ge related optical phonon vibrational peaks in micro-Raman spectra confirm the formation of Ge NCs. Transmission electron microscopy images indicate the formation of Ge NCs after the laser irradiation. The effects of laser pulse energy and the irradiation time play a vital role in the crystallization of the as-deposited films. The changes in the Ge NCs size related shifts in the peak position of Ge optical phonons from the Raman spectra of the respective samples are explained with Ge-Ge optical phonon vibrational model. The observed photoluminescence emission in the green and red region of the visible spectrum from the laser treated samples are explained using the phenomenon of creation of Ge NCs in the Ge+SiO2 composite films and the oxygen defects created in SiO2 during the ns laser treatment.

Precision Layered Stealth Dicing of SiC Wafers by Ultrafast Lasers.

With the intrinsic material advantages, silicon carbide (SiC) power devices can operate at high voltage, high switching frequency, and high temperature. However, for SiC wafers with high hardness (Mohs hardness of 9.5), the diamond blade dicing suffers from problems such as debris contaminants and unnecessary thermal damage. In this work, a precision layered stealth dicing (PLSD) method by ultrafast lasers is proposed to separate the semi-insulated 4H-SiC wafer with a thickness of 508 μm. The laser power attenuates linearly from 100% to 62% in a gradient of 2% layer by layer from the bottom to the top of the wafer. A cross section with a roughness of about 1 μm was successfully achieved. We have analyzed the effects of laser pulse energy, pulse width, and crystal orientation of the SiC wafer. The anisotropy of the SiC wafer results in various qualities of PLSD cross sections, with the roughness of the crystal plane {10−10} being 20% lower than that of the crystal plane {11−20}.

Energy consumption and performance optimisation of laser cleaning for coating removal

Selective removal of coatings by lasers can facilitate the reuse of coated tools in a circular economy. In order to optimise and control the process, it is essential to study the impact of process input variables on process performance. In this paper, coating removal from tooling was carried out using a picosecond a pulsed fibre laser, in order to investigate the effects of laser pulse energy, pulse frequency, galvo scanning speed and scanning track stepover. A fractional factorial design of experiments and analysis of variance was used to optimise the process; considering cleaning rate, specific energy consumption and surface integrity as assessed by changes in surface roughness and composition of the tooling after laser cleaning. The results shows synergy between cleaning rate and specific energy with the laser pulse frequency and galvo scanning speed as the two most significant factors, while the laser pulse energy had the greatest contribution to changes in surface composition. Based on extensive experiments, the relationship between processing rate and system specific energy consumption was mathematically modelled. The paper contributes a new specific energy model for laser cleaning and provides a benchmark of the process energy requirements compared to other manufacturing processes. Additionally, the generic scientific learning from this is that the rate of energy input is a key tool for maximising cleaning rate and minimising specific energy requirements, while the intensity of energy applied, is a key metric that influences surface integrity. More complex factors, influence the surface integrity.

Copper circuits fabricated on flexible polymer substrates by a high repetition rate femtosecond laser-induced selective local reduction of copper oxide nanoparticles.

In this work, copper circuits were fabricated on flexible polyimide (PI) substrates by high repetition rate femtosecond laser-induced selective local reduction of copper oxide nanoparticles (CuO NPs). The effects of laser pulse energy and laser scanning velocity on the quality of the copper circuit were studied. By optimizing laser processing parameters, we prepared a Cu circuit of a line width of 5.5 µm and an electrical resistivity of 130.9 µΩ·cm. The Cu/O atomic ratio of the Cu circuit reaches ∼10.6 and the proportion of Cu is 91.42%. We then studied the formation mechanism of the copper circuit by simulating the temperature field under the irradiation of high repetition rate femtosecond laser pulses. The results show that the thermochemical reduction reaction induced by the high repetition rate femtosecond laser reduces CuO NPs into Cu NPs. Under the thermal effect of the high repetition rate femtosecond laser, Cu NPs agglomerate and grow to form a uniform and continuous Cu circuit.

Numerical simulation of the surface morphology and residual stress field of IN718 alloy by Gaussian mode laser shock

Laser shock processing (LSP) is a new surface modification technology that can improve mechanical properties and extending fatigue life. The numerical simulation was utilized in this work, the IN718 alloy was treated by Gaussian mode laser with the laser pulse energy of 3−7 J, laser pulse width of 12 ns and laser spot in diameter of 3 mm. And the effects of laser pulse energy on the surface morphology and residual stress field of material was investigated. The numerical simulation results showed that after the treatment of LSP, the plastic deformation and compressive residual stress layer with a certain depth is formed on the near surface of material. The amount of the plasticity deformation of material was increased with the laser pulse energy. And the compressive residual stress in surface and the direction of depth are increased with the laser pulse energy too. With the laser pulse energy from 3−7 J, the maximum compressive residual stresses are appeared at the center of the surface corresponding to the laser spot. When the laser pulse energy is increased from 3 J–7 J, the plastic deformation in depth is increases from 0.50 μm–1.86 μm, and the maximum compressive residual stress is increased fromt 362 MPa–742 MPa. In conclusion, LSP can improve mechanical properties of IN718 significantly, and the laser pulse energy is the most important factor to affect the LSP effect. This work can provide a certain theoretical guidance for researchers to study the IN718 alloy treated by LSP.

Ablation and Patterning of Carbon Nanotube Film by Femtosecond Laser Irradiation

Carbon nanotube (CNT) film can be used as thin film electrodes and wearable electronic devices due to their excellent mechanical and electrical properties. The femtosecond laser has the characteristics of an ultra-short pulse duration and an ultra-high peak power, and it is one of the most suitable methods for film material processing. The ablation and patterning of CNT film are performed by a femtosecond laser with different parameters. An ablation threshold of 25 mJ/cm2 was obtained by investigating the effects of laser pulse energy and pulse number on ablation holes. Raman spectroscopy and scanning electron microscope (SEM) were used to characterize the performance of the pattern groove. The results show that the oligomer in the CNT film was removed by the laser ablation, resulting in an increase in Raman G band intensity. As the laser increased, the ablation of the CNTs was caused by the energy of photons interacting with laser-induced thermal elasticity when the pulse energy was increased enough to destroy the carbon–carbon bonds between different carbon atoms. Impurities and amorphous carbon were found at and near the cut edge while laser cutting at high energy, and considerable distortion and tensile was produced on the edge of the CNTs’ groove. Furthermore, appropriate cutting parameters were obtained without introducing defects and damage to the substrate, which provides a practical method applied to large-area patterning machining of CNT film.

Effects of laser pulse energy on the structural, optical and electrical properties of pulsed laser deposited Ga-doped ZnO thin films

Transparent conducting Ga-doped ZnO (GZO) thin films were deposited on glass substrate by pulsed laser deposition (PLD). The effects of laser pulse energy ranging from 80 to 200 mJ on microstructural, surface morphology, electrical and optical properties of GZO films were investigated in detail. XRD patterns have shown that all samples were hexagonal wurtzite structure presenting predominant orientation along the (002) c-axis direction, and the film obtained at 160 mJ showed the optimal crystallinity. The Raman spectra demonstrate that GZO films have oxygen vacancies, Zinc interstitials, and residual stress. The compact, homogenous and flat surface morphology of GZO films were observed by AFM. Hall effect measurements revealed that the electrical properties of samples were dominated largely by the crystallinity and the minimum resistivity of 6.10 × 10−4 Ω cm was obtained when GZO film grown at 160 mJ. Optical transmission spectra displayed an average transmittance higher than 90.6% for all GZO samples in the visible range. The film deposited at 160 mJ exhibited the maximum figure of merit of 22.70 × 10−3 Ω−1, owing to the low resistivity and high transmittance.

Research on Electrolyte Jet Assisted Laser Micromachining Technology

For the traditional laser processing method, processing defects such as recasting layer, microcrack and high concentration of heat affected zone are inevitably generated, which reduces the surface quality and service life of the microstructure. In this paper, the electrolyte jet assisted laser micromachining technology is proposed. This technology applies the laser beam and the corrosive electrolyte jet beam coaxially to the workpiece. At the same time as the laser acts, the corrosive electrolyte jet continuously scour, cool and slightly corrode the processing area. The effect can reduce the thickness of the recast layer, reduce the number of microcracks, and eliminate the high concentration of the heat affected zone. In this paper, the causes of recasting layer in laser processing are analyzed firstly. The material removal mechanism involved in the laser jet assisted laser micromachining and the mechanism of laser coupled electrolyte jet beam are studied. The flow field in the laser jet assisted laser drilling process is established. And the mathematical model of the temperature field; the effects of laser pulse energy, laser repetition frequency, electrolyte concentration and electrolyte jet velocity on the thickness of material recast layer were studied, and the basic processing technology of electrolyte jet assisted laser micromachining was preliminarily mastered, laying the foundation for further research on electrolyte jet assisted laser micromachining technology.

Effect of annealing temperature and laser pulse energy on the optical properties of CuO films prepared by pulsed laser deposition

In this work; copper oxide films (CuO) were fabricated by PLD. The films were analyzed by UV-VIS absorption spectra and their thickness by using profilometer. Pulsed Nd:YAG laser was used for prepared CuO thin films under O2 gas environment with varying both pulse energy and annealing temperature. The optical properties of as-grown film such as optical transmittance spectrum, refractive index and energy gap has been measured experimentally and the effects of laser pulse energy and annealing temperature on it were studied. An inverse relationship between energy gap and both annealing temperature and pulse energy was observed.

Underwater Laser Micromilling of Commercially-Pure Titanium Using Different Scan Overlaps

Underwater laser milling process is a technique for minimizing the thermal damage and gaining a higher material removal rate than processing in air. This paper presents the effect of laser scan overlap on cavity width, depth and surface roughness in the laser milling of commercially-pure titanium in water. The effects of laser pulse energy and pulse repetition rate were also examined, in which a nanosecond pulse laser emitting a 1064-nm wavelength was used in this study. The experimental results indicated that a wide and deep cavity was achievable under high laser energy and large scan overlap. According to the surface roughness, the use of high pulse repetition rate together with low laser energy can promote a smooth laser-milled surface particularly at 50% scan overlap. These findings can further suggest a suitable laser micromilling condition for titanium in roughing and finishing operations.

Influence of ns-laser wavelength in laser-induced breakdown spectroscopy for discrimination of painting techniques

The influence of ns-laser wavelength to discriminate ancient painting techniques such as are fresco, casein, animal glue, egg yolk and oil was investigated in this work. This study was carried out with a single shot laser on samples covered by a layer made of a mixture of the cinnabar pigment and different binders. Three wavelengths based on Nd: YAG laser were investigated (1064, 532 and 266nm). The plasma is controlled at the same electron temperature after an adjustment of pulse energy for these three wavelengths on a fresco sample without organic binder. This approach allows to eliminate the effects of laser pulse energy and the material laser absorption. Afterwards, the emission spectra were compared to separate different techniques. The organic binding media has been separated based on the relative emission intensity of the present CN or C2 rovibrational emissions. In order to test the capability of separating or identifying, the chemometric approach (PCA) was applied to the different matrix. The different solutions in term of wavelength range to optimise the identification was investigated. We focused on the evaluation for the laser wavelength to insure a better separation. The different capacity was interpreted by differentiating the binders by the altered interaction mechanisms between the laser photon and the binders. Also, the electron temperature in the plasma was estimated, which provided the evidences to our findings.

Remote defect visualization of standard composite coupons using a mobile pulse-echo ultrasonic propagation imager

A new laser-ultrasonic-based defect monitoring system, a mobile pulse-echo ultrasonic propagation imager, has been developed to evaluate damage to composite and metallic structures. The system integrates a Q-switched Nd:YAG laser for the generation of thermoelastic waves, a laser Doppler vibrometry sensor for sensing ultrasound and a two-axis translation stage for raster scanning of the combined generation and sensing laser beams. The system allows scanning of both ultrasound generation and sensing laser beams simultaneously. Thus, a full-field pulse-echo ultrasound, as large as the scan area, can be generated that visualizes the longitudinal wave propagation through the thickness. The full-field pulse-echo ultrasonic wave propagation imaging algorithm is used for real-time structural damage evaluation. Four F-16 Lockheed Martin aircraft reference standard composite specimens with different shapes, sizes, thicknesses, compositions, and aspect ratio of damages were tested: the stepped graphite-to-aluminum, the graphite-to-graphite, and the steel-to-graphite composite panel with flat bottom holes and the graphite-to-aluminum core sandwich structure with core missing. Moreover, the effects of laser pulse energy on damage visualization using the system has been presented and tested on the 4-mm-thick aluminum plate with 2-mm-thick wall-thinning. The proposed system successfully detected and visualized all the artificially introduced defects in the standard coupons.

Laser-assisted bioprinting at different wavelengths and pulse durations with a metal dynamic release layer: A parametric study.

For more than a decade, living cells and biomaterials (typically hydrogels) are printed via laser-assisted bioprinting. Often, a thin metal layer is applied as laser-absorbing material called dynamic release layer (DRL). This layer is vaporized by focused laser pulses generating vapor pressure that propels forward a coated biomaterial. Different lasers with laser wavelengths from 193 to 1064 nanometer have been used. As a metal DRL gold, silver, or titanium layers have been used. The applied laser pulse durations were usually in the nanosecond range from 1 to 30 ns. In addition, some studies with femtosecond lasers have been published. However, there are no studies on the effect of all these lasers parameters on bioprinting with a metal DRL, and on comparing different wavelengths and pulse durations – except one study comparing 500 femtosecond pulses with 15 ns pulses. In this paper, the effects of laser wavelength (355, 532, and 1064 nm) and laser pulse duration (in the range of 8 to 200 ns) are investigated. Furthermore, the effects of laser pulse energy, intensity, and focal spot size are studied. The printed droplet volume, hydrogel jet velocity, and cell viability are analyzed.

Surface Morphology of Silicon Induced by Laser Ablation in Flowing Water

Underwater laser machining process has a high potential over the typical laser ablation to remove materials with less thermal damage occurring along the cut. However, the formations of vapor bubble and cut debris in water can substantially disturb the incident laser beam, thereby reducing the ablation performance. Instead of performing the ablation in still water, the flowing water technique was applied to flush away the cut debris and bubble generated. In this study, the effects of laser pulse energy, traverse speed and water flow rate on the cut surface roughness and heat-affected zone in the laser grooving of silicon were experimentally investigated and analyzed. The findings revealed that the cut surface roughness decreased with the increases in laser pulse energy and laser traverse speed. Though a higher water flow rate resulted in a rougher cut surface, the heat-affected zone can be minimized when the increased flow rate was applied.

Study of Composition and Morphology of Cadmium Oxide (CdO) Nanoparticles for Eliminating Cancer Cells

The effects of substrate temperature on the structural, optical, medical and electrical characteristics of Cadmium Oxide (CdO) films are investigated in the current study. Films are deposited on glass substrate at different temperatures, ranged between 450–600 oC, using Spray Pyrolysis Technique. According to X–Ray Diffraction (XRD), it is found that the films are polycrystalline and Cadmium Oxide (CdO) is of a hexagonal wurtzite structure which the preferred direction of its crystal plane is (002). The maximum optical transmittance of films is more than 85%. The size of crystallites is calculated with the maximum value in 500o C. Furthermore, Cadmium Oxide (CdO) nanoparticles were synthesized in deionized water by laser ablation of Cadmium plate. In the current paper, the effects of laser pulse energy and wavelength on the characteristics of Cadmium Oxide (CdO) nanoparticles were studied. Analyses of Transmission Electron Microscope (TEM) were confirmed that size distribution of Cadmium Oxide (CdO) nanoparticles is reduced by increase in laser pulse energy. Fluorescence spectrum of Cadmium Oxide (CdO) nanoparticles shows violet emission accompanied by blue and green band. UV emission with high intensity shows that nanostructure of Cadmium Oxide (CdO) is of a little deficiency. Also, the current study aims to study the linear and non–linear optical characteristics of Cadmium Oxide (CdO) nanoparticles and their applications. Firstly, fluorescence spectrum, as a linear characteristics of Cadmium Oxide (CdO), as well as second harmonic generation and two photons absorption, as non–linear characteristics of Cadmium Oxide (CdO), are studied. Then, some aspects of medicinal and pharmaceutical applications of Cadmium Oxide (CdO) nanoparticles for eliminating cancer cells such as the effect of Cadmium Oxide (CdO) nanoparticles on DNA of human cancer cells and the interaction of Cadmium Oxide (CdO) nanoparticles with DNA of cancer cells are originally investigated. It should be noted that the range of considered parameters are separately clarified and explained in each of related sections (Figure 1).

Effects of laser pulse energy on surface microstructure and mechanical properties of high carbon steel

Surface microstructure and mechanical properties of pearlitic Fe–0.8%C (mass fraction) steel after laser shock processing (LSP) with different laser pulse energies were investigated by scanning electron microscopy(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD) and microhardness measurements. After LSP, the cementite lamellae were bent, kinked and broken into particles. Fragmentation and dissolution of the cementite lamellae were enhanced by increasing the laser pulse energy. Due to the dissolution of carbon atoms in the ferritic matrix, the lattice parameter of α-Fe increased. The grain size of the surface ferrite was refined, and the microstructure changed from lamellae to ultrafine micro-duplex structure (ferrite (α)+cementite (θ)) with higher laser pulse energy, accompanied by the residual stress and microhardness increase.

Direct writing of sub-wavelength ripples on silicon using femtosecond laser at high repetition rate

The near sub-wavelength and deep sub-wavelength ripples on monocrystalline silicon were formed in air by using linearly polarized and high repetition rate femtosecond laser pulses (f=76MHz, λ=800nm, Ͽ=50fs). The effects of laser pulse energy, direct writing speed and laser polarization on silicon surface morphology are studied. When the laser pulse energy is 2nJ/pulse and the direct writing speed varies from 10 to 25mm/s, the near sub-wavelength ripples (NSRs) with orientation perpendicular to the laser polarization are generated. While the direct writing speed reaches 30mm/s, the direction of the obtained deep sub-wavelength ripples (DSRs) suddenly changes and becomes parallel to the laser polarization, rarely reported so far for femtosecond laser irradiation of silicon. Meanwhile, we extend the Sipe⿿Drude interference theory by considering the thermal excitation, and numerically calculate the efficacy factor for silicon irradiated by femtosecond laser pulses. The revised Sipe⿿Drude interference theoretical results show good agreement with the periods and orientations of sub-wavelength ripples.

Effects of Laser Pulse Energy and Annealing Process on Physical Properties of Nanostructured SiO<sub>2</sub> Prepared by Pulse Laser Deposition

Silicon dioxide thin film of different thicknesses has been grown on glass substrate by pulsed laser deposition technique with and without annealing temperature under the vacuum pressure of 8×10-2 mbar. The optical properties such as the absorption, and transmission spectra have been studied for the prepared SiO2 thin film before and after annealing temperature. From the transmission spectra, the optical gap and linear refractive index of the SiO2 thin film was determined. The structure of the SiO2 thin film was tested with X-Ray diffraction, it was formed to be amorphous structure before annealing temperature. The effects of laser pulse energy on the optical properties has been studied before and after annealing temperature. It is found that almost optical properties depends on the laser pulse energy and increases with increasing laser pulse energy and they are enhanced with the annealing temperature. Keywords: SiO2 thin film, pulse laser deposition, annealing temperature.

Effects of Laser Pulse Energy and Annealing Process on Physical Properties of Nanostructured SiO<sub>2</sub> Prepared by Pulse Laser Deposition

Silicon dioxide thin film of different thicknesses has been grown on glass substrate by pulsed laser deposition technique with and without annealing temperature under the vacuum pressure of 8×10-2 mbar. The optical properties such as the absorption, and transmission spectra have been studied for the prepared SiO2 thin film before and after annealing temperature. From the transmission spectra, the optical gap and linear refractive index of the SiO2 thin film was determined. The structure of the SiO2 thin film was tested with X-Ray diffraction, it was formed to be amorphous structure before annealing temperature. The effects of laser pulse energy on the optical properties has been studied before and after annealing temperature. It is found that almost optical properties depends on the laser pulse energy and increases with increasing laser pulse energy and they are enhanced with the annealing temperature. Keywords: SiO2 thin film, pulse laser deposition, annealing temperature.

Laser-induced breakdown spectroscopy enhanced by a micro torch.

A commercial butane micron troch was used to enhance plasma optical emissions in laser-induced breakdown spectroscopy (LIBS). Fast imaging and spectroscopic analyses were used to observe plasma evolution in the atmospheric pressure for LIBS without and with using a micro torch. Optical emission intensities and signal-to-noise ratios (SNRs) as functions of delay time were studied. Enhanced optical emission and SNRs were obtained by using a micro torch. The effects of laser pulse energy on the emission intensities and SNRs were studied. The same spectral intensity could be obtained using micro torch with much lower laser pulse energy. The investigation of SNR evolution with delay time at different laser pulse energies showed that the SNR enhancement factor is higher for plasmas generated by lower laser pulse energies than those generated by higher laser energies. The calibration curves of emission line intensities with elemental concentrations showed that detection sensitivities of Mn I 404.136 nm and V I 437.923 nm were improved by around 3 times. The limits of detection for both Mn I 404.136 nm and V I 437.923 nm are reduced from 425 and 42 ppm to 139 and 20 ppm, respectively, after using the micro torch. The LIBS system with micro torch was demonstrated to be cost-effective, compact, and capable of sensitivity improvement, especially for LIBS system operating with low laser pulse energy.