Laser Energy Flux Research Articles

Micropulse cyclophotocoagulation based on a modified protocol of energy parameters in the treatment of patients with end-stage glaucoma

Purpose: to evaluate the effectiveness of transscleral micropulse cyclophotocoagulation (mCPC) in patients with end-stage glaucoma.Material and methods. 38 patients aged 76.6 ± 7.1 years with end-stage refractory glaucoma were examined, revealing subjective complaints, uncompensated IOP at the maximum hypotensive mode, prior multiple surgical interventions. Indications for mCPC to be performed on a SUPRA 810 device (Quantel Medical, France) according to a modified protocol, in which the laser energy flux is 121.8 J/cm2, were determined. In order to prevent postoperative inflammation after mCPC, a combined drug Floas-T® (glucocorticosteroid fluorometholone + tobramycin) was used.Results. A week after mCPC, the hypotensive effect was achieved in all 38 cases. IOP showed a 30.8 % decrease from the baseline. Considering an additional mCPC given to 14 patients, the entire group showed an IOP 22.8 % decrease (from 34.7 to 26.8 ± 2.9 mm Hg, p < 0.05) achieved after an 18 months’ follow-up. The combined drug Floas-T® was found to contribute to a subjective and clinical improvement, revealing no signs of an increased IOP.Conclusion. The use of mCPC in the treatment of patients with repeatedly operated refractory end-stage glaucoma who receive a maximum hypotensive mode should be estimated as a positive measure. The combined drug based on fluoroquinolone and tobramycin has demonstrated high effectiveness of anti-inflammatory prevention. A survey showed a subjective improvement in the patients’ quality of life. The mCPC method can be recommended as one of the components of a comprehensive rehabilitation program for patients with end-stage glaucoma.

Numerical Simulation and Validation of Multiscale 3D Laser Spiral Machining of Microholes

Femtosecond laser ablation is widely applied in high-precision machining of microholes in aeroengine turbine blades. To further explore the mechanism of action during the laser processing of microholes, numerical simulations were performed on the basis of a molecular dynamics (MD) method coupled with a two-temperature model (TTM). Laser irradiation on the surface of copper for different femtosecond-laser processing parameters is investigated in this work. Through the femtosecond-laser single-pulse central ablation simulation model, the laser energy flux density in a Gaussian laser spot range was discretized and analyzed to calculate the ablation depth at multiple points separately. The cross-sectional morphology of the femtosecond-laser single-pulse ablation pits was approximated and fitted. Finally, a 3D simulation model of the whole process of multiscale femtosecond-laser spiral processing microholes was established by superimposing multipulse femtosecond-laser spiral trajectories. This provides a theoretical basis for analyzing the evolution of geometric parameters and morphological characteristics of the hole during machining with specific laser and process parameters.

A system for the synthesis of nanoparticles by laser ablation in liquid that is remotely controlled with PC or smartphone.

Nanoparticles find applications in multiple technological and scientific fields, and laser ablation in liquid (LAL) emerged as a versatile method for providing colloidal solutions of nanomaterials with various composition, by a low cost, simple, self-standing, and "green" procedure. However, the use of high energy and high power laser beams is harmful, especially when coupled with flammable or toxic liquids, and in situ operation is required for starting, monitoring the LAL synthesis, and stopping it at the desired point. Here we describe the hardware and software design and the test results of a system for the production of nanoparticles by laser ablation synthesis in liquid solution (LASiS), which is remotely controllable with a personal computer or a smartphone. In this system, laser energy and solution flux are selectable, and the synthesis status can be monitored and managed at any time off site. Only commercially available components and software are employed, making the whole apparatus easily reproducible in any LAL laboratory. The system has proven its reliability in various conditions, including intercontinental remote control experiments. Overall, this apparatus represents a step forward to improve the safety and to more efficiently exploit the time of people working with LASiS, thus contributing to the increasing demand for off-site real time monitoring of experimental equipment in many scientific and industrial laboratories, due to safety and efficiency requirements.

Characterization of CO2 laser browning of dough

Abstract We study the application of laser-heating technology to browning dough, due to its potential for high-resolution spatial and surface color control. An important component of this process is the identification of how laser parameters affect browning and baking and whether desirable results can be achieved. In this study, we analyze the performance of a carbon dioxide (CO2) mid-infrared laser (operating at 10.6 μm wavelength) during the browning of dough. Dough samples—consisting of flour and water—were exposed to the infrared laser at different laser power, beam diameter, and sample exposure time. At a laser energy flux of 0.32 MW m−2 (beam diameter of 5.7 mm) and sample exposure time of 180 s we observe a maximum thermal penetration of 0.77 mm and satisfactory dough browning. These results suggest that a CO2 laser is ideal for browning thin goods as well as for food layered manufacture. Industrial relevance A CO2 laser that operates at a wavelength of 10.6 μm (IR) was used as an alternative method for browning dough. The high-power flux of the laser and the high energy absorption of food at this wavelength allow for rapid surface browning; however, the high absorption limits thermal penetration depth. Nevertheless, accuracy of the laser beam enables high resolution spatial and thermal control of the non-enzymatic browning process. This high precision cooking makes laser-browning particularly ideal for food layered manufacture (FLM), a food processing technique that has gained increased attention in recent years. Using FLM, one can adjust the printed layer height to match cooking penetration depth. As a digital manufacturing technology, laser-browning could also enable manufacture of highly complex and customized food geometries and textures.

Visual modeling of laser-induced dough browning

A data-driven model that predicatively generates photorealistic RGB images of dough surface browning is proposed. This model was validated in a practical application using a CO2 laser dough browning pipeline, thus confirming that it can be employed to characterize visual appearance of browned samples, such as surface color and patterns. A supervised deep generative network takes laser speed, laser energy flux, and dough moisture as an input and outputs an image (of 64×64 pixel size) of laser-browned dough. Image generation is achieved by nonlinearly interpolating high-dimensional training data. The proposed prediction framework contributes to the development of computer-aided design (CAD) software for food processing techniques by creating more accurate photorealistic models.

Soft X-ray emission from laser-irradiated gold foils

This paper reports measurements of soft-x-ray emission from gold foils irradiated by 6 ns laser pulses, and analysis and simulations of the observations. These foils can be used as x-ray sources to drive a wide range of experiments. A multichannel, photodiode array measured the time-resolved, soft-x-ray emission. A soft-x-ray framing camera imaged the emission in selected energy bands. Foil thicknesses were from 0.5 to 1.5 μm. The imaging data show that the region emitting soft x-rays grows throughout the laser drive, on both the front and rear surfaces. Analysis of the emitted radiation flux from the rear surface, taking the time-dependent spot size into account, showed that the peak effective temperature of 0.5-μm-thick foils is near 88 eV, while that of 0.75-μm-thick foils is near 78 eV. A Monte Carlo method was used to evaluate the component of the uncertainty in the effective temperature introduced by variations in signal voltages and by uncertainty in the size of the emitting spot. This was found to be near ±2 eV in most cases. Simple theoretical considerations explain the main features of the observations. The Florence code, working with atomic physics from sophisticated models, proved able to reproduce the main features of the observed spectra with 1D simulations in which the laser energy flux was adjusted on the basis of the observed lateral spreading of energy.

Nonlinear Steepening of Density Profile by Intense Laser Radiation in Collisional Inhomogeneous Plasmas

The interaction between a high-power electromagnetic wave with an inhomogeneous underdense plasma is studied by considering the ohmic heating caused by laser radiation. Considering the plasma inhomogeneity and ohmic heating, the nonlinear dielectric permittivity is obtained in the collisional regimes. The wave equation is numerically solved and the electromagnetic fields, electron density, electron temperature, and dielectric permittivity profiles are achieved. These profiles show that in the presence of three density profiles, by increasing the laser energy flux, the modified electron density deviates from background electron density and its structure near the critical density becomes highly peaked. Finally, it is found that the amplitude of electron density distribution decreases by increasing the laser wavelength.

Weakly relativistic and ponderomotive effects in interaction of intense laser beam with inhomogeneous collisionless and collisional plasmas

In this work, the effects of the plasma inhomogeneity and weakly relativistic ponderomotive force due to intense laser radiation on the density profile steepening and dielectric permittivity of plasma are studied in collisionless and collisional regimes. The nonlinear wave equation in the plasma is numerically solved and the electromagnetic field profiles, electron density distribution, and dielectric permittivity variations are achieved in two aforementioned regimes. It is shown that the density profile steepening depends significantly on the laser energy flux and its structure near the critical density becomes highly peaked. The electron temperature distribution in collisional regime is also obtained.

Sub-wavelength temperature probing in near-field laser heating by particles

This work reports on the first time experimental investigation of temperature field inside silicon substrates under particle-induced near-field focusing at a sub-wavelength resolution. The noncontact Raman thermometry technique employing both Raman shift and full width at half maximum (FWHM) methods is employed to investigate the temperature rise in silicon beneath silica particles. Silica particles of three diameters (400, 800 and 1210 nm), each under four laser energy fluxes of 2.5 × 10(8), 3.8 ×10(8), 6.9 ×10(8) and 8.6 ×10(8) W/m(2), are used to investigate the effects of particle size and laser energy flux. The experimental results indicate that as the particle size or the laser energy flux increases, the temperature rise inside the substrate goes higher. Maximum temperature rises of 55.8 K (based on Raman FWHM method) and 29.3K (based on Raman shift method) are observed inside the silicon under particles of 1210 nm diameter with an incident laser of 8.6 × 10(8) W/m(2). The difference is largely due to the stress inside the silicon caused by the laser heating. To explore the mechanism of heating at the sub-wavelength scale, high-fidelity simulations are conducted on the enhanced electric and temperature fields. Modeling results agree with experiment qualitatively, and discussions are provided about the reasons for their discrepancy.

Laser Induced Forward Transfer (LIFT) of Materials using 40 ps Pulses-Experimental and Quantitative Modelisation Study

In this paper we report the results of experiments on LIFT performed using single pulses from a mode locked (40ps pulses), frequency doubled Nd:YAG laser (energy flux ≈ 13J/cm at λ = 532 nm). We studied the controlled transfer of thin films of different metallic materials to a receiving substrate. Optical and scanning electron microscopy (SEM) as well as Energy-dispersive X-ray spectroscopy (EDAX) analysis were performed, showing evidence of the production of micrometric scale patterns. One of our objectives is to investigate and develop possible applications of LIFT in jewellery industry. In order to understand the experimental results we developed a simple analytical model based on the Rankine-Hugoniot relations. Comparison between experimental and simulated results is presented. DOI:10.2961/jlmn.2011.02.0010

Laser-induced forward transfer (LIFT) of material using ablation of thin films

We show the controlled transfer of thin films of different metallic materials to a receiving substrate. Single pulses from a mode locked (40 ps pulse), frequency-doubled Nd:YAG laser (energy flux ≈ 13 J/cm2 at 532 nm) were used. Receiving substrates (metals, semiconductors or crystals) were placed parallel, at a close proximity to the thin film. Optical and scanning electron microscopy (SEM) as well as EDAX analysis were performed, showing evidence of the production of micrometric scale patterns. In particular, we studied the transfer of precious metal to metal/crystals for possible application in the jewellery industry.

Dynamics of plasma formation during quasicontinuous laser irradiation of metals in high-pressure nitrogen atmospheres

This is a study of target destruction and the dynamics of surface plasma formation during the interaction of quasicontinuous laser radiation (λ = 1.06 μm, q = 1-7 MW/cm 2 , τ ∼ 1.5 msec) with D16T duraluminum and bismuth in nitrogen atmospheres at pressures p = 1-20 atm. High speed photography and spectroscopy of the erosion plasma flare are used to determine the onset time for vaporization of the target, as well as the times of appearance of erosion and nitrogen plasmas for different gas pressures and laser energy fluxes q. The emergence of the plasma front from the vapor zone into the surrounding nitrogen is detected experimentally and the properties of the nitrogen plasma are studied.

Nd:YAG laser interaction with titanium implant surfaces for medical applications

Interaction of Nd:YAG laser, operating at 1064 or 532 nm wavelengths and pulse duration of 40 picoseconds, with titanium implant has been studied. Surface damage threshold were estimated to be 0.9 and 0.6 J/cm2 at wavelengths of 1064 and 532 nm, respectively. The titanium implant surface modification was studied at the laser fluence ∼4.0 and 23.8 J/cm2 (at 1064 nm) and 13.6 J/cm2 (at 532 nm). The following titanium implant surface morphological changes were observed: (1) both laser wavelengths cause damage of the titanium in the central zone of the irradiated area (2) appearance of a hydrodynamic feature in the form of re-solidified droplets of the material in the surrounding outer zone with the 1064 nm laser wavelength, and (3) appearance of wave-like microstructures with the 532 nm wavelength. Generally, both laser wavelengths and the corresponding laser energy flux can efficiently enhance the titanium roughness to improve bio-integration with the biological tissues.

Energy characteristics and deposition rates of metals from vacuum laser plasma on dielectric substrates

The effect of the energy flux density of a pulsed Kr-F laser on the processes of generation of the laser plasma of tin, palladium and platinum and on the deposition rates of metal films on dielectric substrates in laser ablation have been studied. The use of the differential scheme of probing a laser plasma with Faraday cups and time-of-flight mass spectrometry has made it possible to distinguish, in plasma ion signals, the ranges of singly charged and multicharged ions, which differ in kinetic energy. The film deposition rate depends on both the laser energy flux density and the degree of ionization of the laser plasma.

Mechanism of laser plasma production and of plasma interaction with a target

A model of plasma production by laser interaction with a solid target was developed taking into account plasma heating by the emitted electrons, as additional to the absorbed laser energy flux, and also target heating by ion bombardment, as additional heat source to the laser radiation. A system of equations, including equations for solid heat conduction, plasma generation, and the plasma expansion, was solved self-consistently. The proposed model allows to understand that the plasma, partially shielding the laser radiation from the target, also converts absorbed laser energies to kinetic and potential energy of the plasma particles, which transport this energy not only in the ambient vacuum but also through the electrostatic sheath to the solid surface.

FE Simulation of Laser Ultrasonic Surface Waves in a Biomaterial Model

This paper describes a study of laser generated ultrasonic waves in an 2-layer elastic, isotropic biomaterial model, in order to establish a modelling technique to simulate the thermoelastic response of high-power short pulse laser beams in human skin. The theory proposed in this paper takes into consideration the fundamental understanding of the laser/material interface. A finite element model using the commercial finite element code ANSYS is used to study the effects of laser pulse duration and energy flux contribution to the surface waves. The simulation comprises a set of boundary conditions that approximate a heat flux point source located on top of the surface of the material. Because of the time scale of interest, the elastic effects do not feed back into the thermal problems, so that a sequential coupled-field analysis was performed where the thermal and elastodynamic fields are uncoupled and treated separately. The initial finite element analysis involves a transient thermal analysis using a heat flux with Gaussian spatial variation to simulate the laser pulse heating. The results from the thermal analysis were read and applied to the structural analysis where the out-of-plane displacements histories are analyzed in the skin model with varying thicknesses

Study on impurity desorption induced by femtosecond pulse laser based on a stochastic process model

With the advantages on non-equilibrium heating and desorption induced by electronic transition, the femtosecond pulse laser introduces a new way for solving the problem of impurity pollution adsorbed on a solid thin film in micro-electro-mechanical systems (MEMS). A model based on stochastic processes was established for stimulated desorption induced by the femtosecond pulse laser to interpret the interaction of the opti-cally excited hot electrons with the adsorbed molecules in a metal substrate. Numerical simulation results reveal a time-dependent desorption probability of adsorbed molecules and indicate that how key parameters of femtosecond pulse laser, such as incident laser energy flux, pulse duration, and wavelength of pulse, have a great effect on the desorption probability.

Screening effects of the excimer laser produced plasma of YBa 2Cu 3O 7

The radiation screening properties of the excimer laser produced plasma of the YBCO high T c superconductor were investigated. The plasma was created as a result of the ablation of bulk YBCO in air, following the absorption of 30 ns duration excimer laser pulses and probed by laser pulses of the same characteristics. Plasma shielding was observed above approximately 1.4 J/cm 2 of laser energy flux. The electron density of the plasma as a function of the laser energy flux, at the beginning of the plasma expansion, was estimated.

Transport Phenomena and Droplet Formation During Pulsed Laser Interaction With Thin Films

This work investigates transport phenomena and mechanisms of droplet formation during a pulsed laser interaction with thin films. The surface of the target material is altered through material flow in the molten phase induced by a tightly focused laser energy flux. Such a process is useful for developing a laser-based micromachining technique. Experimental and numerical investigations of the laser-induced fluid flow and topography variations are carried out for a better understanding of the physical phenomena involved in the process. As with many machining techniques, debris is often generated during laser-material interaction. Experimental parametric studies are carried out to correlate the laser parameters with the topography and droplet formations. It is found that a narrow range of operation parameters and target conditions exists for “clean” structures to be fabricated. The stop action photography technique is employed to capture the surface topography variation and the melting development with a nanosecond time resolution and a micrometer spatial resolution. Numerical simulations of the laser-induced surface deformation are also performed to obtain the transient field variables and to track the deforming surface. The comparison between the numerical and experimental work shows that, within the energy intensity range investigated in this work, the surface deformation and droplet formation are attributed to the surface-tension-driven flow, and the recoil pressure effect plays an insignificant role in the surface topography development. [S0022-1481(00)02903-0]

Effect of Aging on Ignition Delay Times of a Composite Solid Propellant Under CO2 Laser Heating

In this paper, the effect of aging on the ignitibility and reproducibility of a composite solid propellant was investigated. Ignition delay times of solid propellant samples undergone different degrees of aging were determined under various levels of incident CO2 laser energy fluxes. Micrographs obtained from an Environmental Scanning Electron Microscope (ESEM) showed that the surfaces of the aged samples exhibited fiber-like structure as compared to the heterogeneous structure of the as-machined sample. The porosity of the fiber-like structure increased with the degree of aging. Based upon the results of experiments, it was observed that aged propellant samples require much longer heating time to reach self-sustained combustion condition than the as-machined sample at lower energy fluxes (around 50 W/cm2). However, at higher energy fluxes (around 150 W/cm2), the effect of aging on the ignition delay times became smaller.