Absorption Of Laser Energy Research Articles

Stimulated Brillouin scattering of backward stimulated Raman scattering

The rescattering of backward stimulated Raman scattering (BSRS) by stimulated Brillouin scattering (SBS) is found in the high electron density region by relativistic Vlasov-Maxwell simulation and particle-in-cell (PIC) simulation, where the BSRS is in the regime of absolute instability and dominates in all the scatterings. Both one dimension (1D) Vlasov simulation and two dimension (2D) PIC simulation have been given to verify that there exists SBS of BSRS in the regime of absolute instability for BSRS. The SBS of BSRS will be even stronger than forward stimulated Raman scattering (FSRS) and SBS in regime of absolute instability for BSRS. Thus, besides Langmuir decay instability and laser energy absorption, the SBS of BSRS is also an important saturation mechanism of BSRS in high electron density region.

Real-time observation of disintegration processes within argon clusters ionized by a hard-x-ray pulse of moderate fluence

We present a time-resolved study of disintegration within atomic clusters ionized by a hard-x-ray pulse of moderate fluence. It was performed with electron and ion spectroscopy, and complemented by theoretical simulations. The expanding clusters were probed with a near-infrared (NIR) laser pulse over a range of pump-probe delays from -4 to 10 ps. In addition to an increasing number of singly charged atomic ions, originating from the ionization of Rydberg atoms formed through electron-ion recombination, we observe a decrease of oligomer yields. The latter is due to the interaction of oligomers with the NIR probe pulse, leading to their dissociation. At time delays between -1 and 2 ps, efficient absorption of the NIR laser energy occurs, even though the NIR intensity is too low to trigger tuneling ionization of Ar atoms. Our observations are similar to earlier observations of the fragmentation behavior of clusters excited by soft-x-ray pulses. This indicates that the relaxation dynamics of x-ray-excited nano-objects are universal over a wide range of excitation photon energies.

Novel Multifunctional Nanoagent for Visual Chemo/Photothermal Therapy of Metastatic Lymph Nodes via Lymphatic Delivery.

Breast cancer is one of the major diseases that threaten women’s health. Lymph node (LN) metastasis is the most common metastatic path of breast cancer. Finding a simple, effective, and safe strategy to eliminate metastatic tumors in LNs is highly desired for clinical use. Carbon nanoparticles (CNs), as an LN tracer, have been widely used in the clinical setting. In addition, previous experiments have confirmed that CNs have good photoacoustic imaging and photothermal effects. In this study, we used CNs as a photothermal conversion material and drug carrier, poly(lactic-co-glycolic acid) (PLGA) as a film-forming material, and docetaxel as a chemotherapy drug to prepare multifunctional nanoparticles (DOC-CNPs). The prepared DOC-CNPs present as a black solution, which shows smooth spherical particles under light microscopy and transmission electron microscopy (TEM), and they have a good ability for liquid–gas phase transition, good dispersibility, high drug-loading capacity, and low cytotoxicity. In vitro, they can release drugs and inhibit tumor cells after laser irradiation. The photoacoustic (PA) signal intensity and the photothermal conversion efficiency increased with an increase in the concentration of DOC-CNPs. In vivo, after administration, the DOC-CNPs reached the LNs. After laser irradiation, the DOC-CNPs absorbed laser energy, and the temperature of the LNs increased high enough to achieve photothermal therapy under PA and ultrasound monitoring. Fracture of the DOC-CNPs was caused by the liquid–gas phase transition with the increased temperature, and the ruptured DOC-CNPs released docetaxel to achieve targeted chemotherapy. These findings suggested that DOC-CNPs can achieve precise treatment for metastatic LNs of breast cancer with PA and ultrasound visualization.

High throughput lipid profiling for subtype classification of hepatocellular carcinoma cell lines and tumor tissues

Cell heterogeneity of tumor tissues is one of the causes of cancer recurrence after chemotherapy. Cell subtype identification in tumor tissues of specific cancer is critical for precision medicine and prognosis. As the structural and functional components of cells, lipids are closely related to the apparent morphology of cells. They are potential biomarkers of species of cancers and can be used to classify different cancer cell types, but it remains a challenge to establish a stable cell differentiation model and extend it to tumor tissue cell subtype differentiation. Here we describe a lipid profiling method based on nanostructure assisted laser desorption/ionization mass spectrometry (NALDI-MS), which could classify five hepatocellular carcinoma (HCC) cell lines and discriminate subtype of mixed cells and tumor tissues. The NALDI target was patterned with array of sample spots containing vertical silicon nanowires (Si NWs). Owing to its high ability to absorb laser energy, the vertical Si NWs can help to generate abundant lipid ions of cell extracts without need of organic matrix. Combined with statistical analysis methods, twenty-two ion peaks distributed in four MS peak clusters were selected as potential biomarkers to distinguish the subtype of the five HCC cell lines. Peak normalization was performed within each MS peak cluster to reduce the variation of peak intensity in batch to batch analysis. Compared to full-spectrum normalization method, the inner-cluster normalization method could help to distinguish cell subtype more stably and accurately. The molecular structure of these biomarkers was identified and sorted into two classes including phosphatidylcholine (PE, PI, PG, PA, PS) and glycosphingolipid (LacCer, ST). Furthermore, the established method was successfully applied to identify the major HCC cell subtype in mixed cell samples and xenograft tumor tissues as well as drug response test, showing great potential in precision medicine and prognosis.

Mechanical Performance of Polyethylene Joints Based on Nanocomposites Doped with Titanium Dioxide

AbstractTwo sheets of polyethylene (biomedical type) are welded by a diode laser; one of the two layers is doped with titanium dioxide nanoparticles at different concentrations in order to enhance the absorption coefficient at the laser wavelength. The doped nanocomposite plastic has the typical white color of pure polyethylene. Single‐lap geometries are stressed by means of mechanical static lap shear and hardness tests in order to check the change induced by laser energy absorption and choose the best filler amount. These polymeric joints can be useful in biomedical field for the special features of the ultra‐high‐molecular‐weight polyethylene and for the particular advantages of high sealing precision required in medical devices.

Deep cooling characteristics of multi-pulsed cryogen spray: A new technology to assist laser lipolysis

Obesity is a fast growing health problem that may induce severe chronic diseases. Laser lipolysis, as an effective noninvasive treatment, has great potential. Multi-pulsed cryogen spray (MCS) can be used to improve therapeutic effect, particularly by protecting epidermis and dermis from thermal damage caused by the competitive absorption of laser energy between dermal water and subcutaneous fat. Epoxy resin was employed as skin phantom, and surface heat transfer characteristics exposed in deep cooling by continuous and multi-pulsed cryogen spray were investigated by R134a. Findings indicate that MCS is more suitable for laser lipolysis than continuous spray given the deeper cooling depth and better cooling efficiency due to the dispersion of the accumulated liquid film that hinders surface heat transfer. Spatial heat transfer has a large inhomogeneity with short pulse duration and more homogeneity distribution with long pulse duration. The optimal duty cycle of 0.039 obtained good cooling effect without frostbite given the same pulse durations (Δtp) and number of pulses (np). The MCS with parametric settings of Δtp = 10 ms, Δtd (pulse delay) ≥ 1500 ms, np ≤ 10 and Δtp = 30 ms, Δtd ≥ 3000 ms, np ≤ 6 can be used as reference for clinical treatment given their good cooling effect on 2-mm deep dermis without frostbites.

Effect of Q-Switched Nd:YAG laser on the anodization of 1050 aluminum alloy

Short pulses from a Nd:YAG laser effectively enhanced the corrosion resistance of aluminum alloy. Laser heat treatment at energies of 450, 550, 650, and 750 mJ was applied prior to anodization of 1050 aluminum alloy at voltages of 5, 10, and 15 V. The pitting corrosion potential of the anodic oxide layer was investigated in a seawater environment by electrochemical tests, and the corrosion behavior of the aluminum alloy samples was analyzed by polarization and cyclic tests to provide vital information on their corrosion resistance. The corrosion current (Icorr) at 15 V was reduced from 175.47 µA/cm2 to 22.97 µA/cm2 and the potential corrosion (Ecorr) was reduced from −573.4 mV to −334.8 mV by laser treatment. The current density in the cyclic test decreased from 203.58 µA/cm2 to 21.29 µA/cm2 with Laser; the potential corrosion (Ecorr) at 15 V also reduced from −591.9 mV to −358.9 mv. The corrosion resistance for best laser energy was improved at 650 and 750 mJ. Results showed that the oxide layer is influenced by laser treatment. The surface morphology of samples treated before and after laser enhancement was studied, and absorption of laser energy could increase the corrosion resistance of the 1050 aluminum alloy surface. The process and conditions adopted in this paper could improve the pitting corrosion resistance of 1050 aluminum alloy.

Improvement of ablation capacity of sapphire by gold film-assisted femtosecond laser processing

Sapphire is widely used in civilian and military equipment owing to its superior optical and mechanical properties. Femtosecond laser has been demonstrated to be an effective tool to process sapphire material. However, the direct processing of sapphire by femtosecond laser still meets some challenges, such as poor ablation morphology and low laser energy absorption. In this work, femtosecond laser processing of sapphire coated with a 12-nm-thick gold film (Au-coated sapphire) has been investigated. The experimental results have revealed that the ablation morphology of Au-coated sapphire has been improved, featuring fewer molten materials and thermal cracks, as well as regular crater shape and uniform periodic surface structures. It has also been found that, under 100 shots condition, the threshold fluence of Au-coated sapphire is reduced by about 56% compared to that of uncoated one. Meanwhile, the incubation effect of Au-coated sapphire is stronger than that of uncoated one. We also illustrate that the material removal rate of Au-coated sapphire is increased up to about two times higher than that of uncoated one. In order to reveal the effective mechanism of the gold film in the laser processing of sapphire, the energy transfer process among incident photons, free electrons and sapphire lattice phonons was studied. Our study provides a guidance for improving the laser ablation capacity of sapphire.

Time-dependent photothermal characterization on damage of fused silica induced by pulsed 355-nm laser with high repetition rate**Project supported by the National Natural Science Foundation of China (Grant No. 51402173) and the Fundamental Research Funds for the Central Universities, China (Grant No. FRF-TP-15-099A1).

Time-dependent damage to fused silica induced by high frequency ultraviolet laser is investigated. Photothermal spectroscopy (PTS) and optical microscopy (OM) are utilized to characterize the evolution of damage pits with irradiation time. Experimental results describe that in the pre-damage stage of fused silica sample irradiated by 355-nm laser, the photothermal spectrum signal undergoes a process from scratch to metamorphism due to the absorption of laser energy by defects. During the visible damage stage of fused silica sample, the photothermal spectrum signal decreases gradually from the maximum value because of the aggravation of the damage and the splashing of the material. This method can be used to estimate the operation lifetime of optical elements in engineering.

Investigation on Surface Smoothing of Mold Material by Pulsed Laser Irradiation of 532 nm

Manual polishing has been commonly applied as finishing process for metal molds with complicated-shape, but it takes a long time to achieve required surface roughness. Thus, high-efficient polishing method and surface smoothing in micro-areas are required for precise molds. Therefore, the reduction method of surface roughness for metal mold was experimentally investigated by controlling the pulse duration and the waveform in microsecond pulsed Nd:YAG laser irradiation of 532 nm wavelength, which can achieve stable absorption of laser energy even for difficult-to-weld materials with high reflectance. The maximum height roughness can be reduced from 4.0 μm to 1.0 μm by setting an appropriate pulse duration. Excessive heat input generates the edge at the circumference of laser irradiated area due to the movement of molten material. However, control of pulse duration enables the reduction of edge formation. Shorter pulse duration from 2.0 μs to 4.5 μs can perform a wider range of power density without edge formation, compared with longer pulse duration. The range of power density without edge formation can be increased by controlling the temporal input power, which can improve the process controllability of surface smoothing of mold material.

Real-time laser induced chemical derivatizations of peptide N-Terminus for in-situ mass spectrometric sequencing at sub-picomole and nanosecond scale

Distinguishing b- and y-ions is essential to compute amino acid sequences from either N- or C-terminus in mass spectrometry. We described herein a solvent free and real time on-plate derivatization approach that can tag N-terminus of peptides at microliter level with p-chlorobenzaldehyde or 2-hydroxy-5-methylisophthalaldehyde for matrix assisted laser desorption ionization mass spectrometry (MALDI MS). Less than 1 μL of sample solutions can be directly mixed with equal volumes of p-chlorobenzaldehyde or 2-hydroxy-5-methylisophthalaldehyde and α-cyano-4-hydroxycinnamic acid (CHCA), a matrix compound to co-crystalize with analytes for efficient absorption of laser energy and peptide ionization. When the mixture spotted on the sample plate is irradiated with the 3rd harmonic (355 nm) of Nd3+:YAG laser pulses (3 ns width), N-terminal amine groups of peptides instantly react with carbonyl groups of chlorobenzaldehyde or 2-hydroxy-5-methylisophthalaldehyde. Resultant peptides carrying with on-plate formed azomethine group (-CN-) are simultaneously protonated and isolated as precursor ions for subsequent collision-activated dissociation. The mass shift with unique Cl isotopic signature unambiguously distinguishes b ions from y ions and other ions. This method does not need extensive sample preparation and is useful for those samples with limited quantities down to sub-picomole level in sub-microliter volumes. The efficiency was demonstrated with synthetic peptides and tryptic peptides of model proteins. It was found that 2-hydroxy-5-methylisophthalaldehyde provides improved yield for peptides containing lysine residues. Unknown proteins of human saliva and bovine milk as well as phosphopeptides have been identified.

Investigation of subsurface damage density and morphology impact on the laser-induced damage threshold of fused silica.

The laser-induced damage threshold (LIDT) of fused silica is affected by laser field intensity modulation and laser energy absorption. In this paper, the subsurface damage (SSD) density and morphology are detected by the small-angle taper polishing method. The modulation effect of SSD morphology on the incident laser/electric field is analyzed by the finite difference time domain (FDTD) simulation. Finally, the LIDT of the taper polished surface is tested to analyze the relationship among LIDT, SSD density, and SSD morphology, and the results show a high correlation. A reliable regression model is obtained based on the results, which shows that LIDT is inversely proportional to SSD density and the light intensity enhancement factor (LIEF).

Formation of Supercritical Water under Laser Radiation

Abstract—Publications describing the formation of supercritical water (SCW) under laser radiation are summarized, and the control methods for this fast-flowing process are discussed. SCW can appear due to both pulsed and continuous laser irradiation. A primary part of this process is the absorption of laser energy with the transition into heat and/or pressure impulse. Such absorption can proceed in water, targets in contact with water, and in various absorbers in water (for example, metallic or carbon nanoparticles). We have shown that laser methods are effective for transforming water into a supercritical state. The mechanism of action of various laser technologies should take into account the contribution of SCW, because its influence on various processes is often prevalent.

Analysis of the Influence of Laser Parameters on the Microstructure and Surface Properties of Laser Deposited Aluminum Based Coatings

The effects of processing parameters were investigated namely laser intensity and speed of laser scanning of Laser Metal Deposition (LMD) process had on the microstructure, metallurgical evolution, porosity generated in the coating, the geometrical property of the coating and the sizes of the grains in the coating. The processing parameters were applied in combinations in order to find the optimized settings of the process that least affects the metallurgical properties of the Ti-6Al-4V alloy substrate cladded with reinforced aluminium based powder. The temperature gradient and the rate of solidification of reinforcing the Ti-6Al-4V substrate with the aluminium based power were also focused on in terms of how they were influenced by the laser intensity and the scanning speed used in the building process. The inherent material properties were dependent on the process input parameters. The characterized performances considered in the investigation was influenced significantly by the laser processing intensity. The results of the investigation showed that the density had increased in proportion to the increase of the processing laser power coupled with the reduction of the speed of the laser scan. Moreover, for a laser power equivalent to and exceeding 950 W, the density became less susceptible to the laser power. The increased temperature field led to changes in geometry of the coatings as a results of more absorbed laser energy. The materials properties were influenced by the Fe-intermetallic compounds. The molten pool had columnar grains which were fully developed, along its volume as determined in the examination of the microstructure. In the direction of processing, the sample processed at 1.0-1.2 m/min had a reduction in width of the coatings from 1.643 to 1.293 mm and along the height it reduced to 0.375 at 2% Fe and 1% Mn. Increase in the percentage of both Fe and Mn increased the width of the coating to 1.833 mm at 1.0 m/min while the height continued to reduce to minimum of 0.272 mm at 1.2 m/min respectively.

Facile Fabrication of High-Contrast and Light-Colored Marking on Dark Thermoplastic Polyurethane Materials.

In this work, using ferroferric oxide (Fe3O4) and zirconium oxide (ZrO2) as laser-sensitive particles and thermoplastic polyurethane (TPU) as the matrix resin, a series of TPU/Fe3O4/ZrO2 composites were prepared by melt blending, and the effect of the laser marking additive content, composition, and laser marking parameters on the laser marking properties of composites was investigated. The laser marking mechanism of Fe3O4/ZrO2 additives and the role of each component in TPU laser marking were studied by metallographic microscopy, color difference test, scanning electron microscopy, and Raman spectroscopy. Fe3O4 nanoparticles as a laser sensitizer component, on the one hand, can act as a pigment to make the TPU substrate black and, on the other hand, can absorb laser energy to contribute to the formation of laser markings on TPU composite surfaces. In addition, the introduction of ZrO2 nanoparticles can help absorb the laser energy, while the contrast can be improved to enhance the laser marking performance of the TPU composite. Through thermogravimetric analysis, the changes in the thermally stable properties of TPU composites before and after laser marking were investigated, and the results indicated that Fe3O4/ZrO2 nanoparticles can absorb the laser energy, causing melting and pyrolysis of the TPU backbone at a high temperature, to produce a gaseous product resulting in foaming. Finally, the high-contrast and light-colored markings were formed on the black TPU composite surface. This work provides a facile method for producing high-contrast and light-colored markings on the dark TPU composite surface.

Influence of Bulk Temperature on Laser-Induced Periodic Surface Structures on Polycarbonate.

In this paper, the influence of the bulk temperature (BT) of Polycarbonate (PC) on the occurrence and growth of Laser-induced Periodic Surface Structures (LIPSS) is studied. Ultrashort UV laser pulses with various laser peak fluence levels and various numbers of overscans were applied on the surface of pre-heated Polycarbonate at different bulk temperatures. Increased BT leads to a stronger absorption of laser energy by the Polycarbonate. For High Spatial Frequency LIPSS (HSFL), Low Spatial Frequency LIPSS perpendicular (LSFL-I) and parallel (LSFL-II) to the laser polarization were only observed on the rim of the ablated tracks on the surface but not in the center of the tracks. For , it was found that when pre-heating the polymer to a BT close its glass transition temperature (), the laser fluence to achieve similar LIPSS as when processed at room temperature decreases by a factor of two. LSFL types I and II were obtained on PC at a BT close to and their periods and amplitudes were similar to typical values found in the literature. To the best of the author’s knowledge, it is the first time both LSFL types developed simultaneously and consistently on the same sample under equal laser processing parameters. The evolution of LIPSS from HSFL, over LSFL-II to LSFL I, is described, depending on laser peak fluence levels, number of pulses processing the spot and bulk temperature.

Investigation on mechanism of oxide removal and plasma behavior during laser cleaning on aluminum alloy

Through comparing the cleaning effect of aluminum alloy at different energy densities, the model of materials thermodynamics was established, illuminating the cleaning mechanism and plasma behavior. The research showed laser cleaning could remove oxide layer completely. The initial cleaning threshold was 12.7 J/cm2 and complete cleaning threshold was 25.5 J/cm2. At low energy density, phase explosion caused by laser ablation was the main cleaning mechanism. At high energy density, besides phase explosion, impact effect induced by evaporation pressure caused the splattering and removal of oxide layer. Plasma lifespan had positive correlation with energy density. Its lifespan in 25.5 J/cm2 and 51.0 J/cm2 were about 6 μs and above 10 μs, respectively. The model of materials thermodynamics showed that at low energy density, substrate evaporation pushed out molten oxide layer and formed pulse craters. At high energy density, transient energy absorption caused thermal stress coupling effect and separated substrate with oxide layer. The impact effect induced by evaporation pressure resulted in the removal of oxide layer. The vapor of Al absorbed laser energy and formed plasma. The high energy density enhanced the laser-plasma coupling. It caused high temperature and intensive electron density. The time of plasma cooling and atomization became longer.

Exfoliated MXene as a mediator for efficient laser desorption/ionization mass spectrometry analysis of various analytes

The exfoliated MXene (e-MXene) is systematically investigated as a mediator for laser desorption/ionization time-of-flight mass spectrometry (LDI-MS) analysis. Whereas un-exfoliated MXene has no activity for LDI-MS analysis, the e-MXene presents a high resolution, salt-tolerance and efficiency for LDI-MS analysis of various small molecules regardless of their polarity, aromaticity and molecular weight owing to its physicochemical properties such as high laser energy absorption, electrical conductivity and photothermal conversion. Based on our findings, it is clearly confirmed that e-MXene is a promising material for the development of an efficient platform for LDI-MS analysis of small molecules.

Influence of surface plasmon polaritons on laser energy absorption and structuring of surfaces

The accurate calculation of laser energy absorption during femto- or picosecond laser pulse experiments is very important for the description of the formation of periodic surface structures. On a rough material surface, a crack or a step edge, ultrashort laser pulses can excite surface plasmon polaritons (SPP), i.e. surface plasmons coupled to a laser-electromagnetic wave. The interference of such plasmon wave and the incoming pulse leads to a periodic modulation of the deposited laser energy on the surface of the sample. In the present work, within the frames of a Two Temperature Model we propose the analytical form of the source term, which takes into account SPP excited at a step edge of a dielectric-metal interface upon irradiation of an ultrashort laser pulse at normal incidence. The influence of the laser pulse parameters on energy absorption is quantified for the example of gold. This result can be used for nanophotonic applications and for the theoretical investigation of the evolution of electronic and lattice temperatures and, therefore, of the formation of surfaces with predestined properties under controlled conditions.

New Strategy to Achieve Laser Direct Writing of Polymers: Fabrication of the Color-Changing Microcapsule with a Core-Shell Structure.

This paper proposed an efficient and environmentally friendly strategy to prepare a new color-changing microcapsule with a core-shell structure for laser direct writing of polymers, and only the physical melt blending of polymers was employed. The laser absorber (SnO2) and the easily carbonized polymer (PC) were designed as the "core" and the "shell" of the microcapsule, respectively. The microcapsules were in situ formed during melt blending. Scanning electron microscopy, transmission electron microscopy, and energy-dispersive spectrometry confirmed the successful preparation of SnO2/PC microcapsules with a core-shell structure. Their average diameter was 2.2 μm, and the "shell" thickness was 0.21-0.24 μm. As expected, these SnO2/PC microcapsules endowed polymers with an outstanding performance of near-infrared (NIR) laser direct writing. Raman spectroscopy and X-ray photoelectron spectroscopy indicated that the color change was ascribed to the polymer carbonization because of the instantaneous high temperature caused by the SnO2 absorption of NIR laser energy. Optical microscopy observed a thick carbonization layer of 234 μm. Moreover, Raman depth imaging revealed the carbonization distribution, confirming that the amorphous carbon produced by the carbonization of the PC "shell" is the key factor of SnO2/PC microcapsules to provide polymers an outstanding performance of laser direct writing. This color-changing microcapsule has no selectivity to polymers because of providing a black color source (the carbonization of PC) itself, ensuring the high contrast and precision of patterns or texts after laser direct writing for all general-purpose polymers. We believe that this novel strategy to achieve laser direct writing of polymers will have broad application prospects.