Laser Irradiation Experiments Research Articles

Effect of Low Fluence Diode Laser Irradiation on the Hydraulic Conductivity of Perfused Trabecular Meshwork Endothelial Cell Monolayers

Objective: To determine the effect of low-fluence diode laser irradiation upon the fluid perfusion characteristics of cultured human trabecular meshwork cell monolayers when placed in a specially designed testing apparatus and subjected to fluid flow driven by a hydrostatic pressure gradient. Methods: Two experimental series were conducted. In the first series, six low-fluence diode laser irradiation experiments were conducted using cultured human trabecular meshwork cell monolayers grown on filter supports. Upon reaching a steady state perfusion condition at approximately 5.0 mmHg, monolayers were irradiated at fluencies ranging from 0.2619 to 0.8571 J/cm2 using a diode laser (λ = 810 nm). Perfusion and data collection continued for 45 minutes post-irradiation, after which the monolayers were tested to determine post-experimental viability. Hydraulic conductivity values were analyzed for post-irradiation response in 2.5-minute intervals, grouped by viability. In the second series, a total of six irradiated experiments and six simulataneous nonirradiated control experiments were conducted. Fluence values of 0.3571 J/cm2 (n = 3) and 0.4286 J/cm2 (n = 3) were used. Hydraulic conductivity values were analyzed for post-irradiation response in 2.5-minute intervals, grouped by irradiated vs. nonirradiated control groups. Results: In the first series, analysis showed that the viable monolayers exhibited a statistically significant increase in hydraulic conductivity (p < 0.001) from 10 minutes post-irradiation onward. The non-viable monolayers exhibited a statistically significant decrease in hydraulic conductivity. In the second series, irradiated groups showed a significant difference (p < 0.001) from nonirradiated controls from 10 minutes post-irradiation onward. Conclusion: Low-fluence diode laser irradiation increases hydraulic conductivity in viable perfused TM cell monolayers when compared to baseline values or simultaneous nonirradiated controls while decreasing hydraulic conductivity in nonviable monolayers.

Regular 3-D Networks with Clusters for Controlled Energy Transport Studies in Laser Plasma Near Critical Density

Fabrication methods for low-density fine-structure (cell size < 1 μm) 3-D networks of cellulose triacetate (TAC) are developed. Target densities ranged 4-20 mg/cm3, similar polymer structures were produced both with no load and with high-Z cluster dopant with concentration up to 30%. Foams of varying density down to 0.25 plasma critical density at the third harmonic of iodine laser wavelength are supplied for laser shots. Closed-cell and 3-D network structures are considered and monitored as the means of thermal and radiation control in plasma. In comparative foam-and-foil laser irradiation experiments on PALS (Czech, Prague) laser facility the presently developed TAC targets were used along with earlier reported TMPTA (trimethylol propane triacrilate) and agar foams. Radiation transport and hydrodynamic wave velocities proved to be similar in TAC and TMPTA volume structures both having the form of regular 3-D networks, but differed a lot when TAC was compared to agar foams. Radiation transport during laser pulse in TAC doped with Cu-clusters was faster then in TAC with no dopant, whereas plasma from TAC doped with Cu-clusters cooled down quicker then with no clusters. High-Z cluster dopant is effective tool to control energy transport in underdense plasma.

Thermal transient response of membrane-structured-superconducting MgB 2 detector by using 20-ps pulse laser

We carried out 20-ps pulse laser irradiation experiments to a superconducting MgB 2 meander line to understand a thermal excitation and relaxation processes, which are critical for developing as MgB 2 neutron detectors. We observed an exponential thermal–relaxation signal, resulting from pulse laser irradiation. The response time was faster than 1 μs, meaning that the detector would be capable of counting events at a rate of more than 10 6 events per second. The nonequilibrium process was realistically simulated by means of the system of the time-dependent Ginzburg–Landau equation, the Maxwell equation, and the heat diffusion equation.

Three Dimensional Thermal Stress Analysis on Laser Scribing of Glass

Abstract In the laser scribing of glass a thermal stress is introduced into a glass plate by means of CO 2 laser irradiation. The glass plate is rapidly cooled down by water jet immediately after the irradiation. For the purpose of theoretical clarification of the factors ruling the scribable condition and the crack depth, scribable conditions were acquired in laser irradiation experiments using a soda-lime glass plate having a thickness of 0.7 mm. Furthermore, the crack depth and the crack profile were observed for various values of the distance between the heating area and the cooling area. On the basis of the scribable conditions obtained from the experiments, a three-dimensional thermal stress analysis was conducted by a finite element method, allowing the following findings to be obtained. The scribable condition can be estimated from the maximum surface tensile stress in the cooling area and the maximum surface temperature. The crack depth in laser scribing depends on the surface tensile stress in the cooling area and the compressive stress field immediately under that area.

Space weathering of silicates simulated by nanosecond pulse UV excimer laser

Laser irradiation experiments have been performed on powdered silicates (othopyroxene, clinopyroxene, and olivine) using a nanosecond pulse UV excimer laser (193 and 248 nm) to simulate the effects of space weathering induced on minor bodies of the Solar System by micrometeorite bombardment. We have used different fluences (from 0.05 to 2 J/cm 2) to weather the samples, experimenting below and above the ablation threshold. All the irradiated materials have shown reddening and darkening of their UV–vis-NIR reflectance spectra. In addition we have found that: (1) below ablation threshold, weathering effects increase with increasing number of laser pulses, and with increasing fluence, confirming that a thermal process is active; (2) above ablation threshold, weathering is much stronger and efficient than in the previous case, and is independent on the number of pulses. We show that astrophysical time-scales, i.e. times necessary to obtain similar effects on planetary objects, are of about 10 8 yr for both olivine and pyroxene in the case of ablation. The time grows up to 10 10 yr in the case of thermal effects. We infer that micrometeorite bombardment can be rightly simulated by laser irradiation only considering congruent laser ablation.

Detection of Nanostructured Metal in Meteorites: Implications for the Reddening of Asteroids

The association between the most abundant population of meteorites, the ordinary chondrites, and their parent bodies is one of the main topics in the quest to understand the evolution of the solar system. This association is mainly inferred from spectra in visible and near-infrared wavelengths, where many of the asteroids show reddened reflected light curves. The analysis of lunar soils attributed the reddening of the spectra to the presence of nanometer-size metallic particles, and a simulation of micrometeoroid impacts with laser irradiation experiments on terrestrial samples has reproduced this effect and tied it to the vaporization of Fe-bearing silicates. Recently, spacecraft observations have revealed a new mystery in the interpretation of the reddening of S-type asteroids. We have identified an alternative process for surface alteration of airless bodies that can be invoked to solve this mystery through a shock-induced phase transformation of Fe-Ni alloys. These metal phases are usually reported in meteorites but have never been associated with the reddening of the spectra. Here we show, for the first time, atomic force microscopy observations of diffuse nanostructured metal in ordinary chondrites. We also show that the corresponding spectra are unambiguously redder.

Pulse laser irradiation into superconducting MgB2 detector

We performed 20-ps pulse laser irradiation experiments on a MgB2 neutron detector to know a thermal-relaxation process for designing a MgB2 neutron detector. The membrane-type structured MgB2 device was fabricated to minimize the heat capacity of sensing part of a detector as well as to enhance its sensitivity. We successfully observed a thermal-relaxation signal resulting from pulse laser irradiation by developing a detection circuit. The response time was faster than 1μs, meaning that the detector would be capable of counting neutrons at a rate of more than 106 events per second.

Eclipse laser photodetachment method for avoiding probe surface ablation in negative ion measurement

Direct laser irradiation to an electrostatic probe disturbs the negative ion signals of laser photodetachment (LPD) in helium–hydrogen plasmas, particularly when the electron density is considerably high. In order to analyse the characteristics and production mechanism of ablation signals, laser irradiation experiments were performed on a tungsten surface using helium plasmas. To prevent direct laser irradiation to the electrostatic probe tip, a thin wire is installed in the laser channel to form a laser shadow for the probe tip. The ablation signal disappears when the probe tip is fully eclipsed by the laser shadow. The influence of a screening object on the signal intensity of LPD is investigated by experiments and model calculations. It is confirmed that the LPD signal intensity is accurately estimated when some conditions are satisfied, even when a part of the collection region of photodetached electrons is overlapped by the shadow. It is an ablation-free LPD method that can be used to evaluate the negative ion density at a sufficient laser power, even when the ablation disturbs the LPD signals in the conventional LPD technique.

Accelerated ageing of wood Kraft insulating paper by means of a pulsed KrF excimer laser radiation

We report on the successful use of a KrF excimer laser as a highly promising tool to investigate the accelerated ageing of wood Kraft papers used as insulating components in high-voltage power transformers. The effects of varying both the laser repetition rate (5 to 180 Hz) and the laser energy density (0.02 to 0.11 J cm-2) on the degradation of wood Kraft paper in air were systematically investigated. During the laser irradiation experiments, the temperature of the paper samples was real-time measured by means of an IR camera. It is shown that the ageing temperature of the paper can be controlled very precisely by simply adjusting the laser parameters. Indeed, levelling-off temperatures in the 25–320 °C range can be reached after only 3 s of laser exposure, by either varying the repetition rate at a fixed energy density or changing the laser fluence at a given pulse rate. By performing both scanning electron microscopy (SEM) observations and measurements of the degree of polymerization (DPv) of the laser irradiated paper samples, we were able to demonstrate that the laser irradiation induces a very rapid degradation of the paper samples (typical laser exposure times are around 35 s to be compared with ∼10 days for standard dynamic heating based ageing tests). Both the DPv of the irradiated paper samples and the average width of the corresponding cellulose fibers as measured from SEM micrographs, are shown to reduce by about 50% following their laser heating at ∼320 °C for 35 s of exposure time. It is pointed out that the observed laser-induced degradation is predominantly a photothermal process. Finally, by using gas chromatography/mass spectrometry (GC/MS), we were able to show that low molecular weight compounds such as acetaldehyde, methyl formate, acetone, and methanol are produced not only by the laser ageing process but also in real on-field transformers that underwent a severe short-circuit.

Influences of CO 2 laser irradiation on the structure and photoluminescence of zinc oxide thin films

CO 2 laser irradiation experiments on ZnO thin films are reported. The structural, optical, luminescent and vibrational properties of the samples were investigated by X-ray diffraction (XRD), transmittance, photoluminescence (PL) and Raman measurements. XRD results show that the crystalline of the irradiated films was improved. The (002) peaks of irradiated ZnO films shift to higher 2θ angles due to the stress relaxation in the case of laser beam irradiation. From optical transmittance spectra, all films exhibit high transmittance in the visible range, the optical band edge of irradiated films showed a redshift compared with that of as-grown films. Compared with the as-grown films, the photoluminescence emission (in particular the relative intensities of visible emissions) intensities of irradiated samples enhanced. In the Raman scattering spectra, both the A 1 and E 2 modes exhibited slight Raman blueshift.

耳小骨の光吸収スペクトル解析とレーザー照射実験

耳小骨の光吸収スペクトル解析とレーザー照射実験

Sulfur chemistry in laser-simulated impact vapor clouds: implications for the K/T impact event

One of the most promising mechanisms for the mass extinction at the K/T boundary event is blockage of sunlight by sulfuric acid aerosol, which is induced by impact vaporization of sulfate in evaporite deposits around the K/T impact site. One of the advantages of this hypotheses is that it may cause an impact winter much longer than that by silicate dust and soot due to a global wildfire. However, the residence time of sulfuric acid aerosol in the stratosphere depends strongly on the ratio of SO 2/SO 3 in the K/T impact vapor. If SO 3 was dominant, the blockage of sunlight by the sulfuric acid aerosol would not last longer than that by silicate dust and soot. The chemical reaction of sulfur oxides in an impact vapor cloud has not been studied extensively before. This study carries out chemical equilibrium calculations, kinetic model calculations, and laser irradiation experiments with a quadrupole mass spectrometer to estimate the SO 2/SO 3 ratio in the K/T impact vapor cloud. The results strongly suggest that most of sulfur oxides in the K/T impact vapor cloud may have been SO 3, not SO 2. The sulfuric acid aerosol may not have been able to block the sunlight for a long time.

Formation of hydroxyapatite-mediated three-dimensional structures by mouse fibroblasts in response to physical stimulation.

Hydroxyapatite (HAP) ceramics are widely used as implant materials for periodontal bone defects because of their excellent biocompatibility. We demonstrated that physical stimulation, that is, (1). mechanical stimuli or (2). laser irradiation, causes HAP-mediated C3H10T1/2 mouse fibroblasts to form three-dimensional tissue-like structures. Trypsinized 10T1/2 cells were cultured simultaneously with 200 HAP granules on a rotator for 7 days in mechanical stimulation experiments. The cells were later transferred to a regular incubator. Cell reactions were observed by phase-contrast microscopy. The formation of three-dimensional structures around the HAP granules was observed in the third week of cultivation after stimulation. In laser irradiation experiments, trypsinized cells were irradiated with 1, 5, and 16 J/cm(2) at a wavelength of 1000 nm and cultured with 200 HAP granules for 10 weeks. The formation of three-dimensional structures, like those observed in the mechanical stimulation experiments, was observed in the third week after irradiation. The formation of these structures was most frequent at 1 J/cm(2), and the frequency of formation of these structures gradually decreased as the irradiation dose was increased. These results indicate that physical stimuli may stimulate cell proliferation, leading to the repair of damaged tissue. These results also indicate that mouse fibroblasts do not form these three-dimensional structures without HAP and that HAP alone is not sufficient to stimulate the formation of three-dimensional structures.

The great improvement of surface smoothness of CaF 2 in pulsed laser deposition even under the two-photon absorption process

Pulsed laser deposition (PLD) of CaF 2 was performed by employing eclipse (shadow mask) method in addition to the conventional method. Although droplet formation was intercepted by eclipse method, there still remained fragments (∼3 μm) on the deposited surface. The various ways of laser irradiation experiment gives us a new finding and implementation. Fragment-free CaF 2 thin films were successfully obtained by controlling the laser irradiating position in the target (standstill target method) during the deposition even under the two-photon absorption process.

CO&lt;SUB&gt;2&lt;/SUB&gt;レーザーを用いた局麻下喉頭手術

A curved hand-piece CO2 laser was developed to facilitate CO2 laser surgery under topical anesthesia with fiberoptic monitoring. Laser irradiation experiments with the hand-piece demonstrated minimal damage to soft tissues. In a clinical trial, the CO2 laser vaporized a vocal polyp and a vocal nodule. The wound assessment turned out well within a couple of weeks, and the mucosal vibration of vocal cords was preserved. Although the study is preliminary, the newly developed hand-piece proved to be useful in performing CO2 laser surgery under topical anesthesia.

Estimation of Thermal Shock Strength of Cr3C2 Ceramics by Laser Irradiation.

Nuclear power plants have the greatest potential for use in space ships, underwater vehicles, and so on. Because the space and the weight for those plants have limitation, it is very important to develop new radiation shielding materials which have excellent mechanical strength and heat-resistant characteristics. Chromium carbide ceramics (Cr3C2) is the neutron absorber which is more excellent than titanium boride ceramics and has been investigated as a radiation shielding material. This report presents an evaluation of thermal shock strength by the laser irradiation technique for chromium carbide ceramics. Their temperature and thermal stress distributions are analyzed by the finite element method (FEM), and critical fracture curves, which can specify a critical power density for a given laser beam spot diameter, are obtained from the relationships between the spot diameter of the laser beam and the maximum tensile thermal stress. And furthermore, size effects to the fracture criterion of chromium carbide ceramics are examined, and the laser irradiation experiments are performed on chromium carbide ceramics using a CO2 laser. Finally, theoretical results are compared with experimental ones, and the thermal shock strength PL of Cr3C2 ceramics with laser irradiation is ∼3.4 W/mm2 for tension by the FEM analyses.

Laser-induced phase explosion: new physical problems when a condensed phase approaches the thermodynamic critical temperature

Three kinds of thermal processes may lead to material loss from a laser-irradiated surface: 1) vaporization, 2) normal boiling, and 3) explosive boiling. The latter is equivalent to phase explosion. It is appropriate, at this point, to exclude “subsurface heating”, as there are strong doubts about its existence. The relevance of the three processes depends on the laser pulse duration as well as on the temperature attained in the irradiated zone. We revisit the three thermal processes by noting that: 1) vaporization is not important for the shortest time-scales (<1 ns). 2) Normal boiling is subject to a major kinetic obstacle in the process of bubble diffusion, such motion being sufficiently slow that it will simply not occur for t<100 ns. This is because the value of the bubble diffusion coefficient leads to distances traveled which are atomically small for both 1 ns and 100 ns, and for both T=Tm and T=2Tm, with Tm being the melting temperature. 3) Phase explosion, notwithstanding the unfavorable time-scale (1–100 ns) advocated by Martynyuk, as carefully analyzed in this paper, is found to be the most efficient mechanism in the ablation process when looking at thermal processes. Here it should be recognized that a new field in the physics of condensed matter may be emerging when looking at physical properties near the thermodynamic critical temperature, Ttc. In fact, laser irradiation experiments probably represent a unique tool to investigate matter under extreme thermodynamic conditions and on very short time-scales (ps or fs).

Large potential of Sb 100−xTe x films for optical storage

As-grown microcrystalline stoichiometric Sb 40Te 60 films were examined by heat-treatment and laser-irradiation experiments for their potential use in optical storage. Compositional, structural, and optical studies were carried out for films heat-treated at various temperatures in the range 0–260°C. They revealed a stable phase (Sb 60Te 40) in the range 110–185°C and a monotonic decrease of Te below and above this range. The irradiation experiment showed the possibility of both reversible and irreversible phase changes depending on the laser power. Comparing the two experiments, we believe the phase responsible for reversible changes is Sb 100−xTe x (x = 38–45). The irreversible changes were found to be due to large deviation in this stoichiometry.

Effect of heat treatment on the optical properties of amorphous Sb 2S 3 film: The possibility of optical storage

The optical absorbance, refractive index and absorption edge of vapour deposited amorphous Sb 2S 3 films are studied systematically as a function of annealing temperature in the range 160°C > T > 23°C. As deposited films continuously loose sulphur above 60°C as determined by ESCA and this loss affects their measured optical properties. Modification of optical properties upon heating to T = 160°C opens the possibility of a WORM (write once read many times) kind of optical storage as demonstrated in laser irradiation experiment.

Characterization of metallic and ceramic high-temperature materials for energy systems

For the development of metallic and ceramic high temperature materials used, for example, in heat exchanger components, in turbine blades for stationary gas turbines, in ceramic industrial products and fusion reactor components, modern physico-chemical characterization methods are required. The formation stability of naturally formed protective scales is of prime importance in the successful application of metallic materials at high temperatures in aggressive atmospheres. For the characterization and investigation of the growth mechanisms of such surface scales, the main emphasis is placed on such modern spectroscopical methods as SIMS, SNMS, GDOS, EPMA and RBS. The morphology and composition of oxide scales have been investigated by imaging and diffraction techniques. The thermal and mechanical damage behaviour of high-temperature materials for application in fusion reactor components is of importance. Damage behaviour has been simulated by electron beam and laser irradiation experiments, especially by means of in situ techniques in a scanning electron microscope. By such techniques the material erosion, crack formation and crack propagation were studied for ceramic high temperature materials as a function of load parameters. The erosion and the crack formation processes are superim-posed by a redeposition of vaporized material and by thermally activated creep of the binder phases. The application potential for all methods discussed is outlined and available results are presented.