Varying Laser Energy Research Articles

Investigating MALDI MSI parameters (Part 1) – A systematic survey of the effects of repetition rates up to 20 kHz in continuous raster mode

Recent developments in laser performance, combined with the desire for increases in detected ion intensity and throughput, have led to the adoption of high repetition-rate diode-pumped solid-state (DPSS) lasers in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI). Previous studies have demonstrated a more complex relationship between detected ion intensity, stage raster speed and laser pulse repetition rate than the simple linear relationship between number of pulses and detected ion intensity that might be expected. Here we report, for the first time, the interrelated influence of varying laser energy, repetition rate and stage raster speed on detected ion intensity. Thin films of PC 34:1 lipid standard and murine brain tissue with CHCA are analysed by continuous stage raster MALDI MSI. Contrary to previous reports, the optimum laser repetition rate is found to be dependent on both laser energy and stage raster speed and is found to be as high as 20kHz under some conditions. The effects of different repetition rates and raster speeds are also found to vary for different ion species within MALDI MSI of tissue and so may be significant when either targeting specific molecules or seeking to minimize bias. A clear dependence on time between laser pulses is also observed indicating the underlying mechanisms may be related to on-plate hysteresis-exhibiting processes such as matrix chemical modification.

Fabrication and Characterization of Micro-Dent Produced by Laser Shock Peening on Zr-Based Bulk Metallic Glass

A Zr41.2Ti13.8Cu12.5Ni10Be22.5 (vit1) bulk metallic glass was processed by Nd: Glass laser pulses with duration 30ns and energy in the range 20 to 30J. The surface morphology and surface micro-hardness of the vit1 metallic glass, treated with varying laser energy, had been studied in detail. Laser shock peening induced plastic deformation and caused a micro-dent to be generated on the vit1 surface. The optical profiling tests showed that laser pulse energy greatly influenced the diameter and depth of the micro-dents. The surface roughness which was caused by various laser pulse energy was assessed and characterized. The three-dimensional surface topography of the laser treated region on vit1 surfaces had been characterized. In addition the plastic deformation features were also studied.

Surface quality of the curved overhanging structure manufactured from 316-L stainless steel by SLM

The efficiency of fabricating an overhanging structure by selective laser melting (SLM) is an important indicator of the performance of metallic parts. This is due to the fact that defects such as warpage and adherent dross may occur during fabrication of the curved surfaces of overhanging structures. In order to investigate the optimum conditions for fabrication of the curved surfaces of the overhanging structures, experiments were carried out using 316-L stainless steel powder. Initially, the almost 100 % dense parts were fabricated. Then, a model that has a circular curved surface along the Z axis was designed. For a given fabrication depth of 25 μm, several overhanging structures were produced when the laser scanning energy input ranges from 0.15 to 0.6 J/mm. Results show that the upper surface of the almost 100 % dense cube fluctuates like ripples and that the fabrication quality of the curved surface of the overhanging structure varies greatly depending on the energy input and the obliquity angle. For a given energy input of 0.2 J/mm, the obliquity angle for fabricating a totally overhanging surface is as low as 30°. The warpage and adherent dross grow with an increase in the energy input and a decrease in the obliquity angle. Warpage may accumulate, and the accumulated warpage of many layers significantly exceeds the predetermined thickness of the layer. All the four overhanging structures fabricated using varying energy inputs have the following four zones: no dross surface, dense-sinking transition surface, totally sinking surface, and forming failure surface. In the overhanging structures, fabricated with varying laser energy parameters, the angle corresponding to each region was different. The quality of the overhanging surface can be improved by reducing the laser energy. Additionally, a better overhanging surface can be obtained by increasing the obliquity angle. The variation trend of the roughness Rz was almost the same as that of Ra, but the variation range of Rz was much larger than that of Ra. Finally, a foldable abacus with several curved-surface overhanging structures was fabricated to verify the research results. Fundamental methods for controlling and optimizing the SLM-based direct fabrication of curved surfaces of overhanging structures are proposed in this paper, from the perspectives of crafting and design.

Laser alloyed Al-W coatings on aluminum for enhanced corrosion resistance

A tungsten precursor deposit was spray coated on aluminum 1100 substrate and was subsequently surface alloyed using a continuous wave diode-pumped ytterbium laser at varying laser energy densities. For the laser energy input of 21–32J/mm2 the melt depth ranged between 135 and 150μm. Scanning electron microscopy observations indicated the formation of uniform and continuously dense laser alloyed coatings with sound interface between the modified surface and substrate along with an equi-axed grain structure with second phase precipitates in the intergranular region. X-ray diffraction analysis confirmed that laser processing has resulted in the formation of Al4W, as the major phase with retention of W in Al within the alloyed region. The corrosion resistance of laser alloyed coatings was evaluated in near natural chloride solution using ac and dc electrochemical techniques. After laser processing potential–time measurements has indicated the relatively stable and high potential values over the longer exposure times. Cyclic polarization results showed the reduction in the corrosion current density by a factor of 8, compared to untreated Al 1100. Besides, the electrochemical impedance spectroscopy confirmed the increase in the total resistance (47–70kΩcm2) with the increase in the laser energy density.

Characterization of hydroxyapatite coating by pulse laser deposition technique on stainless steel 316 L by varying laser energy

Hydroxyapatite is an attractive biomaterial mainly used in bone and tooth implants because it closely resembles human tooth and bone mineral and has proven to be biologically compatible with these tissues. In spite of this advantage of hydroxyapatite it has also certain limitation like inferior mechanical properties which do not make it suitable for long term load bearing applications; hence a lot of research is going on in the development of hydroxyapatite coating over various metallic implants. These metallic implants have good biocompatibility and mechanical properties. The aim of the present work is to deposit hydroxyapatite coating over stainless steel grade 316 L by pulse laser deposition technique by varying laser energy. To know the effect of this variation, the coatings were than characterized in detail by X-ray diffraction, finite emission-scanning electron microscope, atomic force microscope and energy dispersive X-ray spectroscopy.

Microscopic theoretical investigation on propagation and breakdown depth of ultrashort-pulse laser in dielectrics

Based on the Fokker-Planck equation along with laser propagation equation, a theoretical model that describes the ultrashort-pulse laser propagation characteristics and breakdown in dielectrics is established. Using this model, the conduction band electron densities and the electric field intensities at different positions in a dielectric material at different time are calculated. The variations of reflection, transmittance and energy deposition rate with input laser energy density are discussed. With the threshold conduction band electron density criterion, the breakdown depth in the material under varying laser energy density is calculated, which is found to increase first with laser energy density, and then to decline after reaching a maximum value. Effect of the spatial distribution of laser energy deposition on breakdown depth is analyzed. Meanwhile, the maximum value of breakdown depth is found to decrease as the laser pulse duration becomes shorter.

The ablation threshold of Er:YAG laser and Er,Cr:YSGG laser in dental dentin

This study aims to investigate the threshold dose for the ablation of dentin of human permanent tooth using erbium: yttrium-aluminium-garnet (Er:YAG, wavelength 2.94 μm, pulse duration 100 μs-50 ms) and erbium, chromium: yattrium-scandium-gallium-garnet (Er,Cr:YSGG, wavelength 2.79 μm; pulse duration 140 μs) lasers. A total of 70 dentin samples were subject to the experiment with varying laser energy densities ranging from 0 - 10 J/cm2. The treated dentin surfaces were examined through stereomicroscope and scanning electron microscope. The result of the experiment indicated that both Er:YAG and Er,Cr:YSGG lasers are effective in ablating human tooth dentin. The ablation thresholds for both lasers were determined by inspecting the scanning electron microscopy (SEM) micrographs. The ablation threshold value for Er:YAG laser in dental dentin is 2.97–3.56 J/cm2, and for Er,Cr:YSGG laser, it is 2.69 - 3.66 J/cm2. Key words: Dentin, Er:YAG laser, Er,Cr:YSGG laser, ablation, ablation threshold.

The influence of matrix and laser energy on the molecular mass distribution of synthetic polymers obtained by MALDI-TOF-MS

The molecular mass distribution (MMD) obtained in synthetic polymer characterization by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) may be biased by preferential desorption/ionization of low mass polymer molecules, preferential ion attachment to larger polymers, or degradation and fragmentation due to the desorption process. In this study we focus on the effect of matrix and laser energy on the MMD of four synthetic polymers of low polydispersity with varying thermal stabilities. The four polymers considered were polystyrene (PS), poly(ethylene glycol) (PEG), poly(methyl methacrylate) (PMMA) and poly(tetrahydrofuran) (PTHF). The matrix in which the polymer is analyzed may also influence the laser energy effect of MALDI and was also considered in this paper. Three common matrixes were considered, dithranol, all trans-retinoic acid (RA) and 2,5-dihydroxybenzoic acid (DHB). Statistical analyses of the molecular mass distributions, obtained by varying laser energy and matrixes, reveal trends that can be used to describe the influences of matrix and laser energy on MALDI-TOF-MS data measurement of synthetic polymers. The statistical analysis revealed that the matrix has a greater effect on the polymer MMD than was expected. Polymers analyzed in DHB yielded lower mass moments than polymers analyzed in RA and dithranol. The effects of laser power on the MMD of the polymers were found to be matrix dependent.