Number Of Laser Shots Research Articles

In situ probing of pulsed laser melting and laser-induced periodic surface structures formation by dynamic reflectivity

The melting process and nanostructure formation induced by nanosecond and picosecond laser pulses on bulk silicon and copper thin film were studied by ex situ analysis and in situ real time reflectivity. Three different probing wavelengths (633, 473 and 326 nm) were used during the pump laser processing and were correlated to the beam parameters (pulse duration, laser fluence and number of laser shots) and copper thin film thickness. On a silicon surface using a KrF laser beam (27 ns, 1 Hz, 248 nm), the melting threshold was determined close to 700 mJ cm−2 and the melting duration increased from 10 to 130 ns as the fluence increased from 700 to 1750 mJ cm−2. Nanostructures with a spatial period close to the laser wavelength were formed on both copper thin film and silicon substrate after nanosecond Nd:YAG laser (10 ns, 266 nm, 1 Hz) irradiation. In the picosecond regime, using an Nd:YAG laser (40 ps, 266 nm, 1 Hz), different nanostructures, from spikes to laser-induced periodic surface structures, were formed on 500 nm copper thin film and were analyzed with respect to the drop in dynamic reflectivity changes versus the number of laser shots.

Manufacturing and Spectral Features of Different Types of Long Period Fiber Gratings: Phase-Shifted, Turn-Around Point, Internally Tilted, and Pseudo-Random

The manufacturing and spectral features of different types of long period fiber gratings (LPFGs), ranging from phase-shifted, turn-around point, and internally tilted gratings, to pseudo-random gratings, are described and discussed in detail. LPFGs were manufactured on boron-germanium co-doped photosensitive optical fibers with the point-by-point technique using an excimer KrF laser operating at 248 nm. The developed experimental setup to manufacture high-quality LPFGs was designed to totally customize any type of gratings with the possibility of setting different parameters, such as the grating period (or pitch), the number of grating planes, the number of laser shots for each plane, etc. Some important spectral features of the LPFGs’ spectra were taken into account. This allows realizing homemade devices useful in several fiber-based applications, such as optical filtering, coupling systems, random lasers, physical and chemical sensing, and biosensing.

Effect of laser shock peening on the hardness of AL-7075 alloy

Laser shock peening (LSP) is a surface treatment process for increasing the strength and reliability of metal components. Traditionally applied to composite structures of automotive and medical applications, the LSP technology also shows great potential for aircraft parts to improve the fatigue resistance of highly stressed critical aircraft turbine engine components, complex forming of wing surfaces, steam turbines, etc. The present study investigates the effect of laser peening without coating on the hardness of an aluminium alloy. The Vickers micro-hardness test is used to study the hardness of the Al alloy with different wavelengths and laser intensities. It is found that the metal hardness can be significantly increased to more than 80% by increasing the laser intensity and the number of laser shots irradiated per unit area.

Ultrafast photoionization and excitation of surface-plasmon-polaritons on diamond surfaces

Ultrafast plasmonics of novel materials has emerged as a promising field of nanophotonics bringing new concepts for advanced optical applications. Ultrafast electronic photoexcitation of a diamond surface and subsequent surface plasmon-polaritons (SPPs) excitation are studied both theoretically and experimentally. Following photoexcitation on the rising edge of the pulse, transient surface metallization was found to occur for laser intensity near 18TW/cm2 due to enhancement of the impact ionization rate. In this regime, the dielectric constant of the photoexcited diamond becomes negative in the trailing edge of the pulse thereby increasing the efficacy with which surface roughness leads to inhomogeneous energy absorption at the SPP wave-vector. These transient SPP waves imprint permanent fine and coarse surface ripples oriented perpendicularly to the laser polarization. The theoretical modeling is supported by the experiments on the generation of laser-induced periodic surface structure on diamond surface with normally incident 515-nm, 200-fs laser pulses. Sub-wavelength (Λ≈100nm) and near wavelength (Λ≈450nm) surface ripples oriented perpendicularly to the laser polarization emerged within the ablative craters with the increased number of laser shots. The spatial periods of the surface ripples decrease moderately with the increasing exposure. The comparison between experimental data and theoretical predictions demonstrates the role of transient changes of the dielectric permittivity of diamond during the initial stage of periodic surface ripple formation upon irradiation with ultrashort laser pulses.

Specifications of nanosecond laser ablation with solid targets, aluminum, silicon rubber, and polymethylmethacrylate (PMMA)

The ablation parameters such as threshold fluence, etch depth, ablation rate and the effect of material targets were investigated under the interaction of laser pulse with low intensity. The parameters of the laser system are: laser pulse energy in the range of 110–140 mJ, wavelength 1064 nm and pulse duration 20 ns. By macroscopic estimation of the outward images of the ablation and data obtained, we can conclude that the photothermal and photoionization processes have more influence for aluminum ablation. In contrast, for polymer samples, from the macroscopic observation of the border pattern at the irradiated spot, and also the data obtained from the experiment results, we deduce that both chemical change due to heating and photochemical dissociation were effective mechanisms of ablation. However, concerning the two polymer samples, apart from considering the same theoretical ablation model, it is conceived that the photomehanical specifications of PMMA are involved in the ablation parameters. The threshold fluence for an ablation rate of 30 laser shots were obtained as 12.4, 24.64, and 11.71 J cm−2, for aluminum, silicon rubber and polymethylmethacrylate (PMMA) respectively. The ablation rate is exponentially decreased by the laser-shot number, especially for aluminum. Furthermore, the etch depth after 30 laser shots was measured as 180, 630 and 870 μm, for aluminum, silicon rubber and PMMA, respectively.

Magnetisation switching of FePt nanoparticle recording medium by femtosecond laser pulses

Manipulation of magnetisation with ultrashort laser pulses is promising for information storage device applications. The dynamics of the magnetisation response depends on the energy transfer from the photons to the spins during the initial laser excitation. A material of special interest for magnetic storage are FePt nanoparticles, for which switching of the magnetisation with optical angular momentum was demonstrated recently. The mechanism remained unclear. Here we investigate experimentally and theoretically the all-optical switching of FePt nanoparticles. We show that the magnetisation switching is a stochastic process. We develop a complete multiscale model which allows us to optimize the number of laser shots needed to switch the magnetisation of high anisotropy FePt nanoparticles in our experiments. We conclude that only angular momentum induced optically by the inverse Faraday effect will provide switching with one single femtosecond laser pulse.

Sample exchange by beam scanning with applications to noncollinear pump-probe spectroscopy at kilohertz repetition rates.

In laser spectroscopy, high photon flux can perturb the sample away from thermal equilibrium, altering its spectroscopic properties. Here, we describe an optical beam scanning apparatus that minimizes repetitive sample excitation while providing shot-to-shot sample exchange for samples such as cryostats, films, and air-tight cuvettes. In this apparatus, the beam crossing point is moved within the focal plane inside the sample by scanning both tilt angles of a flat mirror. A space-filling spiral scan pattern was designed that efficiently utilizes the sample area and mirror scanning bandwidth. Scanning beams along a spiral path is shown to increase the average number of laser shots that can be sampled before a spot on the sample cell is resampled by the laser to ∼1700 (out of the maximum possible 2500 for the sample area and laser spot size) while ensuring minimal shot-to-shot spatial overlap. Both an all-refractive version and an all-reflective version of the apparatus are demonstrated. The beam scanning apparatus does not measurably alter the time delay (less than the 0.4 fs measurement uncertainty), the laser focal spot size (less than the 2 μm measurement uncertainty), or the beam overlap (less than the 3.3% measurement uncertainty), leading to pump-probe and autocorrelation signal transients that accurately characterize the equilibrium sample.

An analytical reconstruction model of the spread-out Bragg peak using laser-accelerated proton beams

With the development of laser technology, laser-driven proton acceleration provides a new method for proton tumor therapy. However, it has not been applied in practice because of the wide and decreasing energy spectrum of laser-accelerated proton beams. In this paper, we propose an analytical model to reconstruct the spread-out Bragg peak (SOBP) using laser-accelerated proton beams. Firstly, we present a modified weighting formula for protons of different energies. Secondly, a theoretical model for the reconstruction of SOBPs with laser-accelerated proton beams has been built. It can quickly calculate the number of laser shots needed for each energy interval of the laser-accelerated protons. Finally, we show the 2D reconstruction results of SOBPs for laser-accelerated proton beams and the ideal situation. The final results show that our analytical model can give an SOBP reconstruction scheme that can be used for actual tumor therapy.

An Approach to Reduce the Sample Consumption for LIBS based Identification of Explosive Materials

<p>An experimental design based on spectral construction, which has potential to minimise the sample consumption, the number of laser shots and time required to collect the data from laser induced breakdown spectroscopy for identification of the explosive materials is reported in the study. This approach is an ideal solution in the field of hazardous material detection, where the availability of the sample can be a serious limiting factor. The experimental data recorded on a set of five high energy materials has been considered to test the performance of the proposed methodology. Multiple spectra are constructed by assuming a normal distribution at each wavelength of the spectrum, where random numbers are generated using the mean and standard deviations obtained from arbitrarily chosen five experimental spectra from each class. The newly generated spectra are called as synthetic spectra. The correct classification obtained from – K - nearest neighbour combined with principal component analysis and partial least square – discriminant analysis demonstrated very promising results. The correct classification rates differed by only<br />4 per cent - 7 per cent as compared to conventional approach where experimental spectra alone are considered for the analysis. Further, when RDX is excluded, the obtained results are almost identical with conventional approach.</p>

Statistical analysis of laser driven protons using a high-repetition-rate tape drive target system

One of the challenges for laser-driven proton beams for many potential applications is their stability and reproducibility. We investigate the stability of the laser driven proton beams through statistical analysis of the data obtained by employing a high repetition rate tape driven target system. The characterization of the target system shows the positioning of the target within $\ensuremath{\sim}15\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ in the focal plane of an off-axis parabola, with less than a micron variation in surface flatness. By employing this stable target system, we study the stability of the proton beams driven by ultrashort and intense laser pulses. Protons with maximum energies of $\ensuremath{\sim}6\ifmmode\pm\else\textpm\fi{}0.3\text{ }\text{ }\mathrm{MeV}$ were accelerated for a large number of laser shots taken at a rate of 0.2 Hz with a stability of less than 5% variations in cutoff energy. The development of high repetition rate target system may provide a platform to understand the dynamics of laser driven proton beams at the rate required for future applications.

Histology-Compatible MALDI Mass Spectrometry Based Imaging of Neuronal Lipids for Subsequent Immunofluorescent Staining.

Matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) enables acquisition of spatial distribution maps for molecular species in situ. This can provide comprehensive insights on the pathophysiology of different diseases. However, current sample preparation and MALDI-IMS acquisition methods have limitations in preserving molecular and histological tissue morphology, resulting in interfered correspondence of MALDI-IMS data with subsequently acquired immunofluorescent staining results. We here investigated the histology compatibility of MALDI-IMS to image neuronal lipids in rodent brain tissue with subsequent immunohistochemistry and fluorescent staining of histological features. This was achieved by sublimation of a low ionization energy matrix compound, 1,5-diaminonapthalene (1,5-DAN), minimizing the number of low-energy laser shots. This yielded improved lipid spectral quality and speed of data acquisition and reduced matrix cluster formation along with preservation of specific histological information at cellular levels. This gentle, histology-compatible MALDI-IMS protocol also diminished thermal effects and mechanical stress created during nanosecond laser ablation processes that were prominent in subsequent immunofluorescent staining images but not with classical hematoxylin and eosin (H&E) staining on the same tissue section. Furthermore, this methodology proved to be a powerful strategy for investigating β-amyloid (Aβ) plaque-associated neuronal lipids as exemplified by performing high-resolution MALDI-IMS with subsequent fluorescent amyloid staining in a transgenic mouse model of Alzheimer's disease (tgSwe).

Thermoelectric and Structural Characterization of Al-Doped ZnO/Y₂O₃ Multilayers.

The influence of Y2O3 nanolayers on thermoelectric performance and structure of 2% Al-doped ZnO (AZO) thin films has been studied. Multilayers based on five 50 nm thick AZO layers alternated with few nanometers thick Y2O3 layers were prepared by pulsed laser deposition on Al2O3 single crystals by alternate ablation of AZO target and Y2O3 target. The number of laser shots on Y2O3 target was maintained very low (5, 10 and 15 pulses in three separate experiments. The main phase (AZO) presents polycrystalline orientation and typical columnar growth not affected by the presence of Y2O3 nanolayers. The multilayer with 15 laser shots of Y2O3 showed best thermoelectric performance with electrical conductivity σ 48 S/cm and Seebeck coefficient S = −82 μV/K, which estimate power factor (S2·σ) about 0.03 × 10−3 W m−1 K−2 at 600 K. The value of thermal conductivity (κ) was found 10.03 W m−1 K−1 at 300 K, which is one third of typical value previously reported for bulk AZO. The figure of merit, ZT = S2·σ·T/κ, is calculated 9.6 × 10−4 at 600 K. These results demonstrated the feasibility of nanoengineered defects insertion for the depression of thermal conductivity.

Analysis of Indium Tin Oxide Film Using Argon Fluroide (ArF) Laser-Excited Atomic Fluorescence of Ablated Plumes.

A two-pulse laser-excited atomic fluorescence (LEAF) technique at 193 nm wavelength was applied to the analysis of indium tin oxide (ITO) layer on polyethylene terephthalate (PET) film. Fluorescence emissions from analytes were induced from plumes generated by first laser pulse. Using this approach, non-selective LEAF can be accomplished for simultaneous multi-element analysis and it overcomes the handicap of strict requirement for laser excitation wavelength. In this study, experimental conditions including laser fluences, times for gating and time delay between pulses were optimized to reveal high sensitivity with minimal sample destruction and penetration. With weak laser fluences of 100 and 125 mJ/cm2 for 355 and 193 nm pulses, detection limits were estimated to be 0.10% and 0.43% for Sn and In, respectively. In addition, the relation between fluorescence emissions and number of laser shots was investigated; reproducible results were obtained for Sn and In. It shows the feasibility of depth profiling by this technique. Morphologies of samples were characterized at various laser fluences and number of shots to examine the accurate penetration. Images of craters were also investigated using scanning electron microscopy (SEM). The results demonstrate the imperceptible destructiveness of film after laser shot. With such weak laser fluences and minimal destructiveness, this LEAF technique is suitable for thin-film analysis.

Intraocular Pressure Spikes following Neodymium-doped Yttrium Aluminum Garnet Laser Capsulotomy: Current Prevalence and Management in Israel.

ABSTRACTAim The current treatment for posterior capsular opacification (PCO), neodymium-doped yttrium aluminum garnet (Nd:YAG) laser capsulotomy, may lead to increased intraocular pressure (IOP). Our aim was to survey routines in the management of IOP spikes and to identify the rate of IOP spikes following prophylactic apraclonidine treatment.Materials and methods A survey questionnaire among ophthalmologists and a retrospective registry review was used. Patients were administered apraclonidine 0.5% prior to capsulotomy. The IOP was measured before and 1 hour postprocedure.Results A total of 71% of responders (n = 45) routinely prescribe topical IOP-lowering medication and 82% routinely measure IOP before or after capsulotomy. The registry analysis included 87 eyes of 75 patients. Mean IOP decreased by 0.9 ± 3.3 mm Hg (p = 0.01, range: -6 to 10) following capsulotomy. No patient reached IOP values above 21 mm Hg following the procedure, with 3.4 and 1.1% of patients demonstrating an IOP elevation of more than 3 and 5 mm Hg respectively. No association was found between number of laser shots, mean laser power, or comorbid conditions, such as diabetes, hypertension, or glaucoma status with posttreatment IOP.Conclusion Most ophthalmologists surveyed routinely prescribe prophylactic IOP-lowering medication and measure IOP before or after capsulotomy. Mean IOP remained clinically stable following capsulotomy with prophylactic apraclonidine instillation, and no patient reached IOP values above 21 mm Hg. Differences in laser delivery or comorbid conditions were not associated with posttreatment IOP. Considering that no patient demonstrated a clinically significant IOP spike following prophylactic apraclonidine instillation, perhaps routine measurement of IOP following primary Nd:YAG laser may be reserved for high-risk patients only.Clinical significance In this work, we showed the prophylactic effect of apraclonidine 0.5% and suggest that measuring IOP after the procedure is necessary only in certain high-risk cases, possibly helping to reduce workload and patient waiting time and improving quality of service.How to cite this article Achiron A. Intraocular Pressure Spikes following Neodymium-doped Yttrium Aluminum Garnet Laser Capsulotomy: Current Prevalence and Management in Israel. J Curr Glaucoma Pract 2017;11(2):63-66.

Experimental design for optimizing MALDI-TOF-MS analysis of palladium complexes

This paper presents optimization of matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometer (MS) instrumental parameters for the analysis of chloro(2,2'',2"-terpyridine)palladium(II) chloride dihydrate complex applying design of experiments methodology (DoE). This complex is of interest for potential use in the cancer therapy. DoE methodology was proved to succeed in optimization of many complex analytical problems. However, it has been poorly used for MALDI-TOF-MS optimization up to now. The theoretical mathematical relationships which explain the influence of important experimental factors (laser energy, grid voltage and number of laser shots) on the selected responses (signal to noise ? S/N ratio and the resolution ? R of the leading peak) is established. The optimal instrumental settings providing maximal S/N and R are identified and experimentally verified.

Yttria-Stabilized Zirconia Ceramic Deposition on SS430 Ferritic Steel Grown by PLD - Pulsed Laser Deposition Method

Development of high temperature materials are one of the key issues for the deployment of advanced nuclear reactors due to higher temperature operation. One of the candidate materials for that purpose is ceramic-coated ferritic steel that one of the functions is to be a thermal barrier coating (TBC). Thin films of YSZ (Ytrria-Stabilized Zirconia) ceramic have been deposited on a SS430 ferritic steel using Pulsed Laser Deposition (PLD) at Center For Science and Technology of Advanced Materials laboratory – National Nuclear Energy Agency of Indonesia (BATAN). The thin film was deposited with the chamber pressure range of 200-225 mTorr, the substrate temperature of 800oC, and the number of laser shots of 3×104, 6×104 and 9×104. Afterward, the samples were analyzed using Scanning Electron Microscope – Energy Dispersive X-ray Spectroscope (SEM-EDS), X-Ray Diffractometer (XRD), Atomic Force Microscope (AFM) and Vickers hardness tester. The results showed that the YSZ could homogeneously and sticky deposited on the surface of the ferritic steel. The surfaces were very smoothly formed with the surface roughness was in the range of 70 nm. Furthermore, thickness, composition of Zr4+ dan Y3+, the crystallinity, and hardness property was increased with the increasing the number of the shots.

Structural, electrical, and mechanical characterization of Al 5086 alloy irradiated with 248 nm–20 ns KrF excimer laser

Williamson-Hall analysis of XRD patterns of Al 5086 alloy specimens (10 mm × 10 mm × 6 mm) irradiated with 100–500 KrF excimer laser pulses in air (1 bar) as well as in vacuum (10−3 mbar) was done to evaluate structural changes on laser irradiation. Both crystallite size (30 nm–99 nm) and lattice strain (0.00043–0.00241) were found, in general, to increase with the number of laser shots first rapidly up to 200 and later on rather slowly. Also, for a given number of laser shots, the crystallite size of the specimen laser-irradiated in vacuum was higher than that of the specimens laser-irradiated in air. Harris analysis of XRD patterns revealed that the most preferentially oriented plane was (200) with texture coefficient in the range 2.359–2.982. Electrical resistivity of the specimens was measured by four-point probe technique. It was found to increase with the number of laser shots up to 200, and later on decreases monotonically. However, for a given number of laser shots, its value was higher for the specimen laser-irradiated in air than that for the specimen laser-irradiated in vacuum. On plotting combined surface hardness data for un-irradiated and laser-irradiated specimens in air as well as in vacuum as a function of inverse square-root of crystallite size, a cross over from classical Hall-Petch relation (99 nm–55 nm) to inverse Hall-Petch relation (55 nm–30 nm) occurred at about 55 nm. This is true not only for the surface hardness but also for the hardness measured at 0.5 and 1.0 mm depth below the specimen surface. The intensity of laser-hardening effect gradually diminishes as one goes down from the uniformly laser-irradiated specimen surface to a depth of 3.0 mm below it. The relationship between electrical resistivity and surface hardness was linear.

Surface-pattern geometry, topography, and chemical modifications during KrF excimer laser micro-drilling of p-type Si (111) wafers in ambient environment of HCl fumes in air

Eight mirror-like polished p-type Si (111) wafers were irradiated with 100, 200, 300, 400, 800, 1200, 1600, and 2000 KrF excimer laser pulses in ambient environment of HCl fumes in air. The laser parameters were: wavelength = 248 nm, pulse width = 20 ns, pulse energy = 20 mJ, and repetition rate = 20 Hz. For each set of laser pulses, characterization of the rectangular etched patterns formed on target surface was done by optical/scanning electron microscopy, XRD, and EDX techniques. The average etched depth increased with the increase in number of laser pulses from 100 to 2000 in accord with Sigmoidal (Boltzmann) function, whereas the average etch rate followed an exponential decay with the increase in number of laser pulses. However, the etched area, maximum etched depth, and maximum etch rate were found to increase linearly with the number of laser pulses, but the rate of increase was faster for 100–400 laser pulses (region I) than that for 800–2000 laser pulses (region II). The elemental composition for each etched-pattern determined by EDX shows that both O and Cl contents increase progressively with the increase in the number of laser shots in region I. However, in region II both O and Cl contents attain saturation values of about 39.33 wt.% and 0.14 wt.%, respectively. Perforation of Si wafers was achieved on irradiation with 1200–2000 laser pulses. XRD analysis confirmed the formation of SiO2, SiCl2 and SiCl4 phases in Si (111) wafers due to chemical reaction of silicon with both HCl fumes and oxygen in air.

Analysis of impurities on contaminated surface of the tokamak limiter using laser induced breakdown spectroscopy

Laser induced breakdown spectroscopy (LIBS) analysis of plasma dust/impurities deposited on the surface of graphite limiter of Aditya tokamak is presented in the manuscript. LIBS spectra of contaminated curved surface of the limiter show the presence of Fe, Cr, Ni, Mo, Mn, Cu and C. The depth profile analysis of impurities has been performed by recording LIBS spectra with successive number of laser shots. Variation of spectral line intensity of impurities on its surface with distance from one end of the curved surface to the other end has been studied which shows spatial analysis i.e. deposition pattern of plasma dust/impurities on its surface. The concentration of constituents has been calculated using calibration free LIBS (CF-LIBS) method. The study demonstrates the capability of LIBS for depth profile and spatial analysis of deposited impurities on tokamak limiter.

Impact of 1064 nm–10 ns pulsed laser on the surface morphology, structure, and hardness of Pd80Ni20 alloy

Specimens of Pd80Ni20 alloy were irradiated in air with 70, 80, 90, and 100 laser shots using a Q-switched Nd-YAG laser of 1064 nm wavelength with pulse duration 10 ns, energy 50 mJ, and repetition rate 10 Hz. Surface morphology of the laser-irradiated specimens was studied with the help of a scanning electron microscope. It includes wave-like structures or ripples, dips, ridges, microcones, flakes, and fissures, etc. The X-ray diffraction patterns of un-irradiated and irradiated specimens were analyzed using the Williamson–Hall method to evaluate crystallite size and microstrain. Texture coefficient was determined by Harris analysis. The peak intensity of (111), (200), (220), (311), and (222) planes increases linearly with laser shots, which shows that the concentration of point defects (i.e., vacancies) is progressively decreased on increasing the number of laser shots due to the annealing processes. Surface hardness was measured using a Vickers hardness tester. The average surface hardness of the specimens initially decreases on irradiation with 70 laser shots and later on increases linearly with increase in laser shots up to 100. An inverse Hall-Petch relationship is observed in the crystallite size range 19–27 nm. As crystallite size decreases from 27 to 19 nm, volume fraction of amorphous phase increases progressively. The amorphous phase being softer than crystalline phase due to increased atomic spacing leads to reduction in surface hardness of the material.