Mechanism Of Laser Ablation Research Articles

The Advent of Laser Therapies in Dermatology and Urology: Underlying Mechanisms, Recent Trends and Future Directions

Following their applications in cardiology, ophthalmology and dentistry among others, the advent of lasers in dermatology and urology had become the success story of the past decade. Laser-assisted treatments in dermatology and urology are mainly based on the laser-induced tissue injury/coagulation and/or ablation, depending upon the desirable clinical endpoint. In this review, we discussed the underlying mechanisms of the laser induced tissue ablation. In any medical laser application, the controlled thermal injury and coagulation, and the extent of ablation, if required, are critical. The laser thermal mechanism of injury is intricately related to the selective absorption of light and its exposure duration, similarly to the laser induced ablation. The laser ablation mechanisms were categorized into four different categories (the photo-thermally induced ablation, the photo-mechanically induced ablation, the plasma induced ablation and the photoablation) and their fundamentals are herein described. The brief history of laser treatment modality in dermatology and urology are summarized.

Ablation mechanism study on metallic materials with a 10 ps laser under high fluence

Single shot ablation of metallic materials of aluminium, titanium alloy (Ti6Al4V) and gold has been studied with 10 picoseconds (ps) laser pulses experimentally and theoretically. The ablation rate variation at high fluence was explained by a simplified predictive model based on critical-point phase separation (CPPS) theory. A comparison between experimental and numerical results inferred that CPPS may well be the dominant ablation mechanism for high fluence laser ablation at 10 ps laser duration.

Laser ablation of aluminum from normal evaporation to phase explosion

A study of laser ablation of Aluminum sample by nanosecond laser pulses considering two simultaneous mechanisms of normal evaporation and phase explosion is theoretically carried out. The temperature distribution in the sample is calculated by a one dimensional heat conduction equation. Ablation depth due to the evaporation and explosion is calculated as a function of laser pulse energies. Variation in some effective sample parameters during the laser ablation and their effects on laser ablation mechanisms are taken into account. At low irradiance, ablation is mainly due to the evaporation, while after a threshold intensity, the phase explosion becomes the dominant mechanism. Theoretical results of transition from the normal evaporation to the phase explosion are in good agreement with the experimental results.

Laser Microbeam-induced Spatiotemporal Change in Refractive Index of Chromosomes in Living PTK2 Cells

Ultra-short laser pulses, which allow for confinement of damage to the focal volume, are used routinely to ablate organelles inside living cells, yet the physical mechanisms of this ablation are not completely understood. Many different parameters, particularly wavelength and laser pulse duration, are used in experiments from different laboratories, but no systematic delineation of threshold energy and irradiance for microsurgery of chromosomes using various wavelengths has been reported.In a series of comparative experiments using three different lasers - a 200 femtosecond near-infrared, a 12 picosecond green, and a 12 nanosecond green - we measured energy and irradiance thresholds for inducing a change in the refractive index of micro-irradiated regions of chromosomes in mitotic PTK2 (Potorous tridactylus) kidney cells. To determine the exact irradiance at the focal point, we used the dual objective method for the wavelengths used in our study. While the required energy per pulse for a detectable change in refractive index was highest for the nanosecond laser, the required peak irradiance was highest for the femtosecond laser. The width of the observed damaged spot varied with pulse duration. The threshold for this change in refractive index was found to depend on the spatial pattern of irradiation - point versus line. Further, for a fixed wavelength, the time required to induce a detectable change in the refractive index decreased with increasing exposure time.In addition, a quantitative phase imaging system to quantify the damage in the micro-irradiated regions is being developed. This system will allow more precise quantitation of the change in refractive index in the chromosomes following exposure to the different laser parameters.From these results, specific insights can be gained into the physical mechanisms of laser ablation.

YAGレーザを用いたSnO2系薄膜パターンの高速加工とその加工メカニズムに関する研究

Nano-second pulsed Nd:YAG laser (1064nm) process on SnO2 system thin films on glass as transparent electrode for Flat Panel Displays(FPD) was investigated in this paper. Mechanism of laser ablation, which is an interaction between material and laser, was studied to approach low energy process for mass production application. It was found that carrier concentration is an important factor influencing the process from energy absorption mechanism of free electron vibration induced by laser. The process needed high carrier concentration for low energy process. Experiments showed threshold of the process was about 4.0x1025m-3 of carrier concentration. However, some showed exception of successful process with even low carrier concentration. Then an additional mechanism that YAG photon (1.16eV) excites electrons trapped at deep level to conductive band was inferred. Deep level was measured by cathode luminescence spectroscopy, and result showed existence of electron at less than 1.16eV. It is understood that SnO2 system thin films absorb laser energy through complex process of free electrons vibration and deep level electrons excitation. Considering the mechanisms, it is the first to achieve 20mJ/mm2 of low energy process. This result leads to high process speed and good prospect of the laser process for mass production application for FPD.

고 출력 레이저에 의한 충격파 현상 연구 및 응용

Abstract Ablation occurs at irradiance beyond 10 9 W/cm 2 with nanosecond and short laser pulses focused onto any materials. Phenomenologically, the surface temperature is instantaneously heated past its vaporization temperature. Before the surface layer is able to vaporize, underlying material will reach its vaporization temperature. Temperature and pressure of the underlying material are raised beyond their critical values, causing the surface to explode. The pressure over the irradiated surface from the recoil of vaporized material can be as high as 10 5 MPa. The interaction of high power nanosecond laser with a thin metal in air has been investigated. The nanosecond pulse laser beam in atmosphere generates intensive explosions of the materials. The explosive ejection of materials make the surrounding gas compressed, which form a shock wave that travels at several thousand meters per second. To understand the laser ablation mechanism including the heating and ionization of the metal after lasing, the temporal evolution of shock waves is captured on an ICCD camera through laser flash shadowgraphy. The expansion of shock wave in atmosphere was found to agree with the Sedov’s self-similar spherical blast wave solution.기호설명R : 충격파 반지름 E : 레이저 에너지

Experimental study and numerical simulation of the propulsion of microbeads by femtosecond laser filament

The light filament formed by intense femtosecond laser pulses in air can be used to generate the effective impulse to propel a micro glass bead. In this report, through both experimental studies and the corresponding numerical simulations that involve the dynamics of the nonlinear propagation of light and the laser ablation mechanism, we confirm that this propulsion scheme is based on the laser ablation of the target material. The fundamental characteristics of laser propulsion using a single ultrafast laser filament is also revealed.

Focused ion beam imaging of laser ablation sub-surface effects on layered materials

The focussed ion beam (FIB) represents a useful and versatile tool to allow visualization of sub-surface features related to the thermal effects of laser–target interaction with high spatial resolution. The possibility of performing a contamination-free milling process on specific sample locations provides significant advantage over conventional metallurgical procedures involving cutting and polishing. In particular, the direct visualization of the thermal features occurring at fluences below the phase explosion allows a deeper understanding of the extension of the laser heat-affected zone, the sub-surface alloying processes and additional features related to the photo-thermal mechanism of laser ablation.

Characterization of laser ablation of polymethylmethacrylate at different laser wavelengths

Pulsed laser ablation of polymethylmethacrylate (PMMA) in high vacuum was investigated by using different laser beams. A Nd:Yag laser, working at fundamental (1064 nm) and second harmonics (532 nm) with 9 ns pulse duration and 800 mJ maximum pulse energy was used at INFN-LNS of Catania. Two excimer UV lasers working at 308 nm (XeCl) and 248 nm (KrF) with 20 ns pulse width and 600 mJ maximum pulse energy was used at INFN-LEAS of Lecce. The laser ablation effects on the PMMA were investigated by using similar experimental set-ups and fluences ranging between 2 and 20 J/cm2. A 200 amu mass quadrupole spectrometer was employed to detect ‘on line’ the atom and molecular species emitted in vacuum by the laser ablation process. The ablation yield increases with the laser wavelength, demonstrating that IR radiation induces photothermal effects. The molecular fragmentation increases with the photon energy, demonstrating that photochemical effects become predominant for UV radiation. An investigation about the possible laser ablation mechanisms of PMMA, depending on the laser parameters, will be presented and discussed.

Radiation mechanism of pulsed laser ablation of metal Al

Time-resolved measurement of plasma emission spectra by pulsed XeCl excimer laser ablation of Al under different conditions is reported. The experimental results show that plasma emission spectra are composed of atomic spectrum, univalent ion spectrum and continuous radiation. The atomic spectrum intensity and duration is most significant, the next is the univalent ion spectrum, the continuous radiation is weakest. The detailed mechanism of species excitation is discussed. The continuum radiation comes from electron bremsstrahlung and recombination of electron and ion, the primary atomic and univalent ion excitation originate from recombination of ion and electron. The experimental results are qualitatively explained with the mechanism.

Influence of water-layer thickness on Er:YAG laser ablation of enamel of bovine anterior teeth

Different ideas have been presented to describe the mechanism of augmented laser ablation of dental enamel with different shapes by adding water to the working environment. In this study, the influence of water-laser interaction on the surface of enamel during ablation was investigated at a wavelength of 2.94 microm with different distances between the laser tip and the enamel surface. A motion-control system was used to produce linear incisions uniformly on flat enamel surfaces of bovine anterior teeth, with free-running Er:YAG laser very short pulses (pulse length = 90-120 micros, repetition rate = 10 pulses per second). Four different output energies (100, 200, 300 and 400 mJ) were radiated on samples under distilled water from different distances (0.5, 0.75, 1, 1.25, 1.75 and 2.00 mm). The tooth slices were prepared with a cutting machine, and the surfaces of the ablated areas were measured with software under a light microscope. The average and standard deviation of all cut areas in different groups were reported. There was no significant difference when using a different pulse ablation speed (cm(3)/J) and a water-layer thickness between the tip and enamel surface of 0.5-1.25 mm with energy densities of 30-60 J/cm(2) (200-400 mJ). However, using an output energy of 15 J/cm(2) (100 mJ) and a thicker water layer than 1 mm, a linear ablation did not take place. This information led to a clearer view of the efficiency of Er:YAG laser in the conditions of this study. There are several hypotheses which describe a hydrokinetic effect of Er,Cr:YSGG. These basic studies could guide us to have a correct attitude regarding hydro-mechanical effects of water, although the wavelength of 2.78 microm has a better absorption in hydroxyl branch of water molecules. Therefore, our results do not directly interrupt with the series of investigations done with Er,Cr:YSGG. Water propagation and channel formation under water are investigated during the ablation of tooth enamel with the Er:YAG laser from different distances. Comparing the results of this study with the same research done with water/air spray concludes that the bubble formation and channel propagation in water with this wavelength leads to a more symmetric (linear) ablation process with cavity-preparation-recommended parameters.

Laserowe modyfikowanie materiałow polimerowych. Cz. III. Ablacja laserowa i zmiany struktury geometrycznej powierzchni

The basic mechanisms of laser ablation of polymeric materials were presented. Two main types of ablation were discussed: photochemical and photothermal ones, occurring commonly in actual conditions. The most important factors influencing the course of ablation and the results of the process were characterized, both these concerning irradiation acting and those concerning the material modified. The model of the process, being the base for ablation depth calculation, was described. Most important geometric structures of the surfaces modified with laser irradiation - coherent periodic or incoherent (conical or dendritic) ones - were presented. The possibilities of wide applications of laser ablation in polymeric materials treatment were noticed.

Study of visible and mid-infrared laser ablation mechanism of PMMA and intraocular lenses: experimental and theoretical results

Laser-polymer interactions have attracted extensive attention both for understanding the inherent basic ablation mechanism and for development of tissue simulators in several biomedical laser applications such as in human ophthalmology. Ablation experiments were performed on polymethylmethacrylate used as cornea tissue simulator and PMMA intraocular lenses. The polymer-ablation mechanism was examined with two different wavelengths and pulse durations. The experiments were conducted with Nd:YAG and Er:YAG solid-state lasers, and the ablation rates were simulated by a mathematical model in each case. Furthermore, to investigate the role of tissue hydration during laser ablation, we performed a set of experiments in which Er:YAG laser ablation of hydrophilic acrylic intraocular lenses, with different H(2)O and D(2)O concentrations, was studied. The hydrophilic acrylic lenses with the higher concentration of H(2)O gave the most satisfactory results regarding both the ablation efficiency and the quality of the ablated craters.

Synthesis of CaWO4 nanocolloidal suspension via pulsed laser ablation and its optical properties

Pulsed laser ablation (PLA) in the liquid phase was successfully employed to synthesize calcium tungstate (CaWO4) nanocolloidal suspension. The crystalline phase, particle morphology and laser ablation mechanism for the colloidal nanoparticles were investigated using XRD, TEM and SEM. The obtained colloidal suspension consisted of well-dispersed CaWO4 nanoparticles which showed a spherical shape with sizes ranging from 5 to 30 nm. The laser ablation and the nanoparticle forming process were discussed under consideration of the photo-ablation mechanism, where the nanoparticles were generated by rapid condensation of the plume in high pressured ethanol vapor. The optical properties of the prepared CaWO4 colloidal nanoparticles were analyzed in detail using XPS, Raman spectroscopy, UV-Vis spectroscopy and PL spectrophotometry. The optical band gap was estimated by Tauc and Menths law.

Molecular dynamics simulation of ultrafast laser ablation of fused silica

Ultrafast laser ablation of fused silica is studied using molecular dynamics simulations. Ionization and generation of free electrons, absorption of the laser energy by free electrons and energy coupling between free electrons and ions are considered. The BKS potential is used to describe molecular interactions and is modified to include the effect of free electrons. Temperature, density, and material removal are computed, and the thermal and non-thermal mechanisms of ultrafast laser ablation of fused silica are discussed.

Plume investigations of the mechanisms of SiO laser ablation at 266 nm

The ablation mechanism of SiO at the laser wavelength of 266 nm has been investigated by characterizing the composition and dynamics of neutral and charged particles produced in the ablation. The neutral and ionized composition of the plume and the dynamics of neutral SiO were investigated by time-of-flight mass spectrometry. The velocity distribution of neutral SiO molecules shows contributions of slow and fast components. The velocity distributions of charged species in the plume were investigated by a Langmuir probe technique, obtaining that the distributions shift towards higher velocities with increasing distance from the target surface. The fastest component of the velocity distribution of neutral SiO overlaps the slowest part of the velocity distribution of charged species. The average rotational energy of SiO molecules, estimated by LIF spectroscopy does not allow to draw clear conclusions about the participation of silicon oxide ion clusters as the precursors of fast SiO molecules in the plume.

Femtosecond laser-induced cleaving of protein crystal in water solution

For precise X-ray diffraction (XRD) measurement giving the three-dimensional structure of proteins, it is important to prepare high-quality single crystals with suitable shape. As a new processing technique to obtain such protein crystals, we employed femtosecond laser-induced cleaving of protein crystal in a growth vessel containing water solution. An intact protein crystal was precisely processed without mechanical contact in its sealed growth vessel by focusing femtosecond laser pulses. We confirmed that three-dimensional processing of the crystal in its supersaturated solution was realized using multiphoton absorption and that the processing was efficiently enhanced by the cleaving behavior attributed to a photomechanical mechanism of the femtosecond laser ablation.

IR laser ablation of doped poly(methyl methacrylate)

We investigate the TEA CO 2 laser ablation of films of poly(methyl methacrylate), PMMA, with average M W 2.5, 120 and 996 kDa doped with photosensitive compounds iodo-naphthalene (NapI) and iodo-phenanthrene (PhenI) by examining the induced morphological and physicochemical modifications. The films casted on CaF 2 substrates were irradiated with a pulsed CO 2 laser (10P(20) line at 10.59 μm) in resonance with vibrational modes of PMMA and of the dopants at fluences up to 6 J/cm 2. Laser induced fluorescence probing of photoproducts in a pump and probe configuration is carried out at 266 nm. Formation of naphthalene (NapH) and phenanthrene (PhenH) is observed in NapI and PhenI doped PMMA, respectively, with relatively higher yields in high M W polymer, in similarity with results obtained previously upon irradiation in the UV at 248 nm. Above threshold, formation of photoproducts is nearly complete after 200 ms. As established via optical microscopy, bubbles are formed in the irradiated areas with sizes that depend on polymer M W and filaments are observed to be ejected out of the irradiated volume in the samples made with high M W polymer. The implications of these results for the mechanisms of polymer IR laser ablation are discussed and compared with UV range studies.

Mechanism of ablation of CdS at laser wavelengths in the visible and in the UV

The mechanisms of laser ablation of CdS targets at different laser wavelengths have been investigated. (CdS) n + cluster formation is only observed upon 532 nm ablation. The time and energy distributions of neutral S, S 2, Cd and CdS show significant dependence on laser wavelength. Bimodal distributions are observed at 266 and 308 nm. For the former, the average kinetic energy increases significantly with mass, taking values in the range of 0.3–1.7 eV. At 308 nm the slow component of the time distribution disappears at distances above the target larger than 1 cm. At this wavelength, the observed time distribution appears to reflect mainly the dynamics of the expansion. At 532 nm the time distribution is monomodal and the average kinetic energies are below 0.2 eV. Clear indications of the participation of thermal (at 532 nm) and non-thermal mechanisms (at 266 nm) have been found. It is tentatively concluded that the cluster formation observed upon ablation at 532 nm can be related to the thermal ablation mechanisms in which the low kinetic energy of the species in the plume and their similar velocities favor the aggregation processes.

Infrared and ultraviolet laser ablation mechanisms of SiO

The mechanisms of SiO ablation have been investigated at laser wavelengths in the infrared, at 10.53 μm, and in the ultraviolet at 248 nm. The energy content of the SiO molecule in the plume and the occurrence of phase transformations in the target, are studied as a function of wavelength and fluence of the ablation laser. At 10.53 μm, in the range of fluences of 0.6–3.0 J cm-2, time distributions of ejected SiO, measured at different distances above the surface target are characteristic of thermal ablation, yielding estimated temperatures of the surface in the range from 1300 to 4800 K. The energy channelled as rotational excitation of ejected SiO, scales with increasing fluence. The time distributions of SiO in the plume, obtained at 248 nm laser ablation, are measured at different distances above the target, yielding velocity and energy distributions that shift towards higher values with distance and show a weak tendency to decrease with increasing laser fluence. Raman analysis of the postablated SiO targets irradiated at 10.53 μm, at fluences above 0.6 J cm-2, shows the formation of Si nanocrystals whose size increases with fluence. Phase transformation is not observed at the shorter laser ablation wavelength.