Laser Absorption Efficiency Research Articles

Impact of SWCNTs and CMCS on efficacy of anastomosis and optical properties in vivo during laser biological tissue soldering

In order to improve the mechanical properties of skin tissue incision, enhance laser absorption efficiency, further shorten healing time and reduce skin fibrosis tendency, this study investigated the effects of CMCS or SWCNT combined with 25 % BSA and 0.4 % ICG on laser tissue welding. Nd:YAG pulsed laser was used for wound closure test on live rats with an energy density of 67.3 J/cm2 and linear scanning of skin incisions. The effects of different types and concentrations of biological dressings on wound closure were tested at different sites. The results showed that biocompatible dressings containing CMCS and SWCNTs had a significant effect in promoting wound healing after laser welding. After laser welding, the tensile strength of the control group without CMCS or SWCNTs was only between 6.5 and 9.8 N/cm2, while that with CMCS reached as high as 26.5 N/cm2. Macroscopic morphology analysis showed that components such as CMCS and SWCNTs could significantly shorten healing time from 14 days to 9–10 days. Optical performance tests demonstrated that a combination of 5 %CMCS and 4 %SWCNTs can significantly increase skin's absorption coefficient for laser photons up to7-8 Lg-1cm−1 and reduce photon diffuse reflectance. HE and Masson staining revealed that when internalized by dressing containing 0.4 %SWCNTs, nanocarbon particles promoted collagen skeleton regeneration but increased fibrosis tendency after 14 days post-laser welding, resulting in unfavorable long-term healing outcomes. However, the combination of CMSC with SWCNTs can significantly improve incision mechanical properties, laser photon absorption rate, and shorten healing time while reducing scar proliferation tendencies.

Space-time dependent non-local thermal transport effects on laser ablation dynamics in inertial confinement fusion

In inertial confinement fusion (ICF), electron thermal transport plays a key role in laser ablation and the subsequent implosion processes, which always exhibits intractable non-local effects. Simple modifications of the local Spitzer–Härm model with either an artificially-assumed constant flux limiter or a purely time-dependent one are applied to explain some experimental data, but fail to simultaneously reproduce the space-time evolution of the whole laser ablation process. Here, by carrying out a series of one-dimensional and two-dimensional radiation hydrodynamic simulations where the space-time-dependent non-local thermal transport model proposed by Schurt, Nicolaï and Busquet (the SNB model) are self-consistently included, we systematically study the non-local effects on the whole laser ablation dynamics including those occurring at the critical surface, the conduction zone and the ablation front. Different from those obtained previously, our results show that due to the non-local heat flow redistribution and redirection, at the critical surface the thermal flux is more inhibited, in the conduction zone the lateral thermal transport is suppressed, and ahead of the ablation front the plasma is preheated. When combined together they eventually result in significant improvement of the laser absorption efficiency, extension of the conduction zone, increase of both the mass ablation rate and shock velocity. Furthermore, the dependence of these laser ablation dynamics on different drive laser intensities is investigated, which provides beneficial enlightenments on potential laser pulse shaping and/or ignition scheme optimization in ICF.

Effect of different pulse shapes on the laser welding of aluminum and copper

The Nd: YAG laser is utilized to weld 1060 aluminum (Al) and 110 copper (Cu) with a thickness of 0.4 mm. The effect of different pulse shapes on the microstructure, mechanical and electrical properties of Al-Cu lap joints are investigated by using of the optical microscopy, scanning electron microscope (SEM), tensile test device and micro-resistance tester, respectively. This investigation provided a detailed understanding of how the different pulse shapes influence the metal mixing and the formation of intermetallic compounds (IMCs). The results indicate that the pulse shape with an initial preheating phase improved the laser absorption efficiency. Additionally, this pulse shape resulted in less dissimilar metal mixing compared to the pulse shape that maintained the maximum power throughout. Furthermore, the pulse shape in which the laser power was linearly increased and then maintained at maximum power reduced the formation of IMCs at the joint interface. As a result, the joint exhibited mechanical strengths up to 92 % of the Al base material and similar electrical conductivity. The study provides theoretical guidance on how to utilize pulse shape modulation in laser welding to achieve optimal mechanical and electrical properties in typical joints between Al tabs and Cu busbars.

Demonstration of efficient relativistic electron acceleration by surface plasmonics with sequential target processing using high repetition lasers

For high repetition ultrahigh-intensity laser system, automatic alignment of structured target is key to achieving consistent particle acceleration and plasma heating. In this work, we demonstrate efficient electron acceleration with two sequential steps of laser processing using a high repetition rate, 30-fs ultrahigh-intensity laser. The first pulse does laser machining and creates a steep cylindrical crater on the surface of a flat stainless-steel target. The crater is formed by the hydrodynamic expansion of the heated surface and by spallation of the inner, deeper material by nonthermal relativistic electrons. The crater shape is well controlled and reproducible with 200 \ensuremath{\mu}m width and 350 \ensuremath{\mu}m depth. The second pulse irradiates deeply inside the crater and interacts with the crater wall, efficiently accelerating electrons via surface plasmonic, without need for target realignment. The laser absorption efficiency increases from 32.5 to 97.5% by the process.

Reduced Graphene Oxide/Polydimethylsiloxane as an Over-Coating Layer on Quartz Tuning Fork for Sensitive Light-Induced Thermoelastic Spectroscopy

A novel near-infrared light-induced thermoelastic spectroscopy (LITES) based on a multilayer surface-coated quartz tuning fork (QTF) is proposed for gas detection. Thin-film of reduced graphene oxide (rGO) and polydimethylsiloxane (PDMS) is successively coated on the surface of QTF to improve the laser absorption and thermoelastic conversion efficiency, respectively. NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> is selected as the target analyte for the measurements. The experimental results indicate that introducing a thin layer of PDMS-rGO composite allows a maximum gain factor of 8.64 and 5.53 for the signal amplitude and signal-to-noise ratio (SNR), respectively, compared to a commercial standard QTF. A minimum detectable concentration of 8.98 ppmv was obtained, improved by 5.12 times than that of a bare QTF, and a normalized noise equivalent absorption coefficient (NNEA) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${1.53}\times {10}^{-{9}}\,\text {cm}^{-{1}} \cdot \text {W} \cdot \text {Hz}^{-\text {1/2}}$ </tex-math></inline-formula> was achieved. The results of Allan deviation analysis show that the detection sensitivity reaches 2.63 ppmv when the averaging time is 555 s. The research work and related results have laid a good foundation for trace gas detection by the cost-effective and easy-to-operate infrared sensor.

High absorption efficiency by high intensity laser irradiating carbon aerogel targets

We have proposed a scheme to increase the ultra-intense femtosecond laser absorption efficiency by using carbon aerogel targets. Particle-in-cell simulations show that, compared to a homogeneous target of the same density, the carbon aerogel target can significantly enhance the laser absorption efficiency, and the maximum laser absorption efficiency can reach 88%. Such high absorption efficiency can be attributed to the porous structure and larger surface area of carbon aerogel than ordinary materials, which allows the laser to enter more of the target and interact more fully with the particles inside rather than being reflected off the surface. By studying the interaction between the laser and the carbon aerogel targets, we found that both the nanoparticle diameter and porosity have great effects on the laser absorption efficiency, which is enhanced significantly as the nanoparticle diameter and porosity increase. Such carbon aerogel targets should have significant applications in the fields of laser generation of x rays and high energy density physics.

Efficient absorption of laser light by nano-porous materials with well-controlled structure

The absorption of high-power nanosecond laser pulses in a porous matter is investigated through theoretical and numerical calculations. The effects of structural properties of the porous target such as size of pores and thickness of solid elements on the laser absorption are investigated. The time and space-dependent absorption coefficient of the laser created partially homogenized plasma is used in a plasma hydrodynamic code to reproduce the laser absorption and plasma formation processes in a porous matter. It is observed that the structural characteristics of the porous material can be optimized to significantly increase the laser energy absorption. For porous targets with pore sizes in the range 30–60 nm a value around 1000 nm could be desirable for the wall thickness to increase the laser absorption efficiency to more than 90%. The results can be advantageous in production of efficient laser absorber targets which are desirable in advanced applications such as inertial confinement fusion and laser-plasma x-ray sources.

Influence of the pump scheme on the output power and the intensity noise of a single-frequency continuous-wave laser.

The influence of the pump scheme on the intensity noise of the single-frequency continuous-wave (CW) laser is investigated in this paper, which is implemented in a single-frequency CW Nd:YVO4 1064 nm laser by comparing the traditional 808 nm pumping scheme (TPS) to the direct 888 nm pumping scheme (DPS). Under the conditions that the lasers with TPS and DPS have the same cavity structure and the cavity mirrors, as well as the same operation state including the thermal lens of the laser crystals and the mode-matching between the pump laser mode and the laser cavity mode at the laser crystals, the output power of the laser with DPS is up-to 32.0 W, which is far higher than that of 21.1 W for the laser with TPS. However, the intensity noise of the DPS laser including resonant relaxation oscillation (RRO) frequency of 809 kHz, RRO peak amplitude of 31.6 dB/Hz above the shot noise level (SNL) and the SNL cutoff frequency of 4.2 MHz, respectively, is also higher than that of 606 kHz, 20.4 dB/Hz and 2.4 MHz for the TPS laser. After further analyses, we find that the laser crystal with high doping concentration and long optical length is employed for DPS laser in order to improve the pump laser absorption efficiency, which can simultaneously increase the dipole coupling between the active atoms and the laser cavity, and then results in a high RRO frequency with a large amplitude peak as well as a high SNL cutoff frequency of the laser.

Laser sintering of cryogenically ground polymer powders into high-performance parts: The role of dry particle coating with a conductive flow agent

The poor processability of cryogenically ground polymer powders rendered by their irregular shapes greatly hinders their applications in the selective laser sintering (SLS) technique. In this study, nonconductive silica (SiO2) nanoparticles and conductive carbon black (CB) nanoparticles were coated onto cryogenically ground polyamide 12 (PA12) powders and acted as flow agents to alleviate the flow problem. It was found that the addition of SiO2 or CB nanoparticles both greatly improved the flowability of cryogenically ground powders, thereby facilitating a successful sintering process. However, significantly improved mechanical performance and reduced structural defects were achieved only upon the addition of CB nanoparticles. The underlying mechanism was suggested to be related with the higher conductivity, lower friction, smaller adhesion energy and higher laser absorption efficiency of CB-coated powders. Therefore, conductive and radiation-adsorbing particles such as CB can serve as a multifunctional agent to enable the sintering of polymer powders with irregular shapes into parts with improved mechanical performance.

Influence of laser surface melting on the properties of MB26 and AZ80 magnesium alloys

In the present investigation, laser surface melting (LSM) was performed on MB26 and AZ80 magnesium alloys and their surface properties were evaluated. The finite element method (FEM) was used to calculate the resulting temperature during the laser surface melting process. The melted layer average thickness values were about 296 and 190 μm for MB26 and AZ80 alloys, respectively and the variation in the thickness is mainly attributed to the absorption in laser energy. The average grain size of the LSMed MB26 alloy was decreased about 14.5 times and AZ80 had very finer grains than the MB26 along with the fine distribution of second phases. Further, the X-ray diffraction results revealed that the second phase intensities were decreased in both the alloys due to their dispersion. The laser absorption efficiency of MB26 was higher due to the higher plasma attachment during LSM process, thereby has higher melt layer thickness compared to AZ80. The refined microstructure of the melted layer resulted in an increase of micro-hardness up to 110 Hv. Potentiodynamic polarization test results revealed that the corrosion current density (icorr) values of the LSMed MB26 and AZ80 alloys were decreased about 1.8 and 2.5 times, respectively compared to the as-received alloys. A variation in solidification rates of the melt pool due to the alloying elements were attributed to an improvement in the surface and electrochemical properties.

Maximizing magnetic field generation in high power laser–solid interactions

In order to understand the transport of fast electrons within solid density targets driven by an optical high power laser, we have numerically investigated the dynamics and structure of strong self-generated magnetic fields in such experiments. Here we present a systematic study of the bulk magnetic field generation due to the ponderomotive current, Weibel-like instability and resistivity gradient between two solid layers. Using particle-in-cell simulations, we observe the effect of varying the laser and target parameters, including laser intensity, focal size, incident angle, preplasma scale length, target thickness and material and experimental geometry. The simulation results suggest that the strongest magnetic field is generated with laser incident angles and preplasma scale lengths that maximize laser absorption efficiency. The recent commissioning of experimental platforms equipped with both optical high power laser and X-ray free electron laser (XFEL), such as European XFEL-HED, LCLS-MEC and SACLA beamlines, provides unprecedented opportunities to probe the self-generated bulk magnetic field by X-ray polarimetry via Faraday rotation with simultaneous high spatial and temporal resolution. We expect that this systematic numerical investigation will pave the way to design and optimize near future experimental setups to probe the magnetic fields in such experimental platforms.

Elimination of radiation damage in Tm-doped silica fibers based on the radical bleaching of deuterium loading

We present the deuterium-loading induced radical recovery of 2µm laser fiber and absorption efficiency in thulium (Tm)-doped silica fibers under gamma irradiation in the range of 185Gy-1000Gy. The optical-optical efficiency and fiber cladding absorption spectra of the Tm-doped silica fibers with multi-dose irradiation and deuterium treatment have been measured. It was found that the reduction of the optical-optical efficiency and the additional absorption, both induced by irradiation, were positively associated with the dose. Under the deuterium loading, the efficiencies of the multi-irradiated TDFs could be restored to above 91.9% of the pristine, and the radiation induced absorptions were almost completely vanished. The results indicate that deuterium-loading has an extensive prospect for the radiation hardness of Tm-doped silica fiber.

Prussian blue decorated mesoporous silica hybrid nanocarriers for photoacoustic imaging-guided synergistic chemo-photothermal combination therapy.

The fabrication of nanotherapeutic systems capable of stimuli-responsive drug delivery and photoacoustic imaging (PAI)-guided photothermal therapy (PTT) is considered significant for chemo-photothermal therapy applications in cancer therapy. In the present study, the Prussian blue nanoflake (PBNF) decorated mesoporous silica hybrid nanoparticle (PB@MSH-EDA NPs) is reported for PAI-guided chemo-photothermal therapy applications. The amine group enriched mesoporous silica channels can be used to encapsulate an anticancer drug for chemotherapy, and the surface decorated PBNFs can convert a near-infrared (NIR) laser (808 nm) into heat for photothermal therapy and can also be used for PAI applications. The PB@MSH-EDA NPs show pH-responsive drug release efficiency under acidic pH (pH 5.0 and 4.0) conditions. Furthermore, the PB@MSH-EDA NPs system shows strong NIR laser absorption and photothermal conversion efficiency under 808 nm laser irradiation. The in vitro experimental result shows that the PB@MSH-EDA NPs are biocompatible and could be efficiently taken up by MDA-MB-231 cells. In addition, the in vivo results demonstrate that the tumor-bearing mice fully recovered after injecting the drug (Dox)-loaded PB@MSH-EDA/Dox NPs and being further irradiated with the 808 nm laser. We believe that the PB@MSH-EDA NPs system could be utilized as an efficient PAI-guided chemo-photothermal therapy agent for the detection and treatment of tumors in an emerging cancer therapy application.

Simulation of femtosecond laser absorption by metallic targets and their thermal evolution

AbstractThe interaction of femtosecond laser with initially cold solid metallic targets (Al, Au, Cu, Mo, Ni) was investigated in a wide range of laser intensity with focus on the laser energy absorption efficiency. Our developed simulation code (FEMTO-2D) is based on two-temperature model in two-dimensional configuration, where the temperature-dependent optical and thermodynamic properties of the target material were considered. The role of the collisional processes in the ultrashort pulse laser–matter interaction has been carefully analyzed throughout the process of material transition from the cold solid state into the dense plasma state during the pulse. We have compared the simulation predictions of the laser pulse absorption with temperature-dependent reflectivity and optical penetration depth to the case of constant optical parameters. By considering the effect of the temporal and spatial (radial) distribution of the laser intensity on the light absorption efficiency, we obtained a good agreement between the simulated results and available experimental data. The appropriate model for temperature-dependent optical parameters defining the laser absorption efficiency will allow more accurate simulation of the target thermal response in the applications where it is critical, such as prediction of the material damage threshold, laser ablation threshold, and the ablation profile.

Silver-gold alloy nanoparticles as tunable substrates for systematic control of ion-desorption efficiency and heat transfer in surface-assisted laser desorption/ionization.

Systematically controlling heat transfer in the surface-assisted laser desorption/ionization (SALDI) process and thus enhancing the analytical performance of SALDI-MS remains a challenging task. In the current study, by tuning the metal contents of Ag-Au alloy nanoparticle substrates (AgNPs, Ag55Au45NPs, Ag15Au85NPs and AuNPs, ∅: ∼2.0 nm), it was found that both SALDI ion-desorption efficiency and heat transfer can be controlled in a wide range of laser fluence (21.3 mJ cm-2 to 125.9 mJ cm-2). It was discovered that ion detection sensitivity can be enhanced at any laser fluence by tuning up the Ag content of the alloy nanoparticle, whereas the extent of ion fragmentation can be reduced by tuning up the Au content. The enhancement effect of Ag content on ion desorption was found to be attributable to the increase in laser absorption efficiency (at 355 nm) with Ag content. Tuning the laser absorption efficiency by changing the metal composition was also effective in controlling the heat transfer from the NPs to the analytes. The laser-induced heating of Ag-rich alloy NPs could be balanced or even overridden by increasing the Au content of NPs, resulting in the reduction of the fragmentation of analytes. In the correlation of experimental measurement with molecular dynamics simulation, the effect of metal composition on the dynamics of the ion desorption process was also elucidated. Upon increasing the Ag content, it was also found that phase transition temperatures, such as melting, vaporization and phase explosion temperature, of NPs could be reduced. This further enhanced the desorption of analyte ions via phase-transition-driven desorption processes. The significant cooling effect on the analyte ions observed at high laser fluence was also determined to be originated from the phase explosion of the NPs. This study revealed that the development of alloy nanoparticles as SALDI substrates can constitute an effective means for the systematic control of ion-desorption efficiency and the extent of heat transfer, which could potentially enhance the analytical performance of SALDI-MS.

Control of laser absorbing efficiency and proton quality by a specific double target

The micro-structured double-layer target is an efficient method to improve proton quality. However, the laser absorption efficiency is low due to strong reflection at the front surface of such targets. Moreover, the proton charge is limited by the driving laser radius. To overcome these shortcomings, a specific double-layer (SDL) target with a vacuum gap in the center of the heavy ion layer is proposed in this paper. In this specified target, the laser reflection effect is significantly weakened and the absorption and penetration efficiencies are greatly enhanced. The high-energy electrons from Breakout afterburner regime efficiently transfer their energy to the protons. Both the energy of the spectral peaks and maximum proton energy are greatly increased. The periodic structure of the longitudinal electric field makes the force applied on the protons becomes homogeneous in time average and therefore reduce the energy spread. In these SDL targets, the proton layer radius and the accelerated proton charge are not limited by the laser radius. With a larger-radius proton layer, the protons can be accelerated to high energy with small energy spread. When the proton layer radius is reduced to the laser radius, the SDL target is still an effective structure to improve the proton quality. The mechanism is proved by a series of particle-in-cell simulations.

Laser-filamentation-induced water condensation and snow formation in a cloud chamber filled with different ambient gases.

We investigated femtosecond laser-filamentation-induced airflow, water condensation and snow formation in a cloud chamber filled respectively with air, argon and helium. The mass of snow induced by laser filaments was found being the maximum when the chamber was filled with argon, followed by air and being the minimum with helium. We also discussed the mechanisms of water condensation in different gases. The results show that filaments with higher laser absorption efficiency, which result in higher plasma density, are beneficial for triggering intense airflow and thus more water condensation and precipitation.

Reinjection of transmitted laser light into laser-produced plasma for efficient laser ignition.

For improving the laser absorption efficiency in laser ignition, the transmitted laser light was returned to the laser-produced plasma by using a corner cube. In the experiments, the transmitted light was reinjected into the plasma at different times. The laser absorption efficiency was found to be substantially improved when the transmitted light was reinjected into the plasma after adequate plasma expansion. Furthermore, through visualization experiments on gas-dynamics phenomena, it was found that the reinjection of the transmitted light affected not only the laser absorption efficiency but also the gas dynamics after breakdown, and thereby the initial flame kernel development.

Selection of powder or wire feedstock material for the laser cladding of Inconel® 625

The selection of the feedstock material form significantly affects the temperature and resulting distortion generated during laser cladding. An experimental investigation is undertaken to characterize the differences in temperature and deformation histories resulting from laser cladding using powder and wire. While both feedstock produce good quality clads, the powder clad is nearly twice as thick as the wire clad. In situ measurements show that the selection of a powder feedstock results in higher temperatures and greater deformation. However, characterization of the final distortion shows that each clad twists the substrate by nearly the same amount. Thermo-mechanical modeling of the process shows that the disparity in laser absorption efficiency is responsible for the variation in temperature between the powder and wire. Simulations of a multi-layer deposition show that although a single wire layer generates lower temperatures and less deformation than a single powder layer, the wire clad will actually produce greater total deformation because two layers are required to achieve the same thickness as the powder clad.

Correlation between laser absorption and radiation conversion efficiency in laser produced tin plasma

The correlation between the laser absorption and the conversion efficiency (CE) for 13.5 nm extreme ultraviolet (EUV) light in a laser-produced tin plasma was investigated. The absorption rate α and the CE were measured simultaneously for a laser-pre-formed low-density tin target as a function of the time delay between the pre-pulse and the main laser pulse. A clear and positive correlation between α and CE was found with increasing delay time; however, the CE decreases rapidly at longer delay times. This result is partly attributed to a reduction in the absorption rate, but is mainly attributed to the self-absorption of EUV light in excessively long-scale plasmas.