Tritium recovery from co-deposited layers using 193-nm laser

Recovery of tritium from co-deposited layers formed in deuterium–tritium plasma operations of the TFTR (Tokamak Fusion Test Reactor) was investigated by the use of an ArF excimer laser operating at the wavelength of 193 nm. At the laser energy density of 0.1 J/cm², a transient spike of the tritium-release rate was observed at initial irradiation. Hydrogen isotopes were released in the form of hydrogen-isotope molecules during the laser irradiation in vacuum, suggesting that tritium can be recovered readily from the released gases. In a second experiment, hydrogen (tritium) recovery from the co-deposited layers on JT-60 tiles that had experienced hydrogen-plasma operations was investigated by laser ablation with a focused beam of the excimer laser. The removal rate of the co-deposited layers was quite low when the laser energy density was smaller than the ablation threshold (1.0 J/cm²), but reached 1.1 μm/pulse at the laser energy density of 7.6 J/cm². The effective absorption coefficient in the co-deposited layers at the laser wavelength was determined to be 1.9 μm^-1. The temperature of the surface during the irradiation at the laser energy density of 0.5 J/cm² was measured on the basis of Planck’s law of radiation, and the maximum temperature during the irradiation decreased from 3570 K at the initial irradiation to 2550 K at the 1000th pulse of the irradiation. Received: 5 August 2002 / Accepted: 7 August 2002 / Published online: 28 October 2002 RID="*" ID="*"Corresponding author. Fax: +81-29/2825917, E-mail: shu@tpl.tokai.jaeri.go.jp     

Caries resistance of lased human root surface with 10.6 μm CO2 laser-thermal,morphological, and microhardness analysis

Although the cariostatic effects of CO₂ laser on enamel have been shown, its effects on root surface demineralization remains uncertain. The objectives of this in vitro research was to establish safe parameters for a pulsed 10.6 μm CO₂ laser and to evaluate its effect on morphological features of the root surface, as well as on the reduction of root demineralization. Ninety-five human root surfaces were randomly divided into five groups: G1-No treatment (control); G2—2.5 J/cm²; G3—4.0 J/cm²; G4—5.0 J/cm²; and G5—6.0 J/cm². Intrapulpal temperature was evaluated during root surface irradiation by a thermocouple and morphological changes were evaluated by SEM. After the surface treatment, the specimens were submitted to a 7-day pH-cycling model. Subsequently, the cross-sectional Knoop microhardness values were measured. For all irradiated groups, intrapulpal temperature changes were less than 1.5°C. Scanning electron microscopy images indicated that fluences as low as 4.0 J/cm² were sufficient to induce morphological changes in the root surface. Additionally, for fluences reaching or exceeding 4.0 J/cm², laser-induced inhibitory effects on root surface demineralization were observed. It was concluded that laser energy density in the range of 4.0 to 6.0 J/cm² could be applied to a dental root to reduce demineralization of this surface without compromising pulp vitality.     

Absorption and thermal study of dental enamel when irradiated with Nd:YAG laser with the aim of caries prevention

It is widely recognized that Nd:YAG can increase enamel resistance to demineralization; however, the safe parameters and conditions that enable the application of Nd:YAG laser irradiation in vivo are still unknown. The aim of this study was to determine a dye as a photoabsorber for Nd:YAG laser and to verify in vitro a safe condition of Nd:YAG irradiation for caries prevention. Fifty-eight human teeth were selected. In a first morphological study, four dyes (waterproof India ink., iron oxide, caries indicator and coal paste) were tested before Nd:YAG laser irradiation, under two different irradiation conditions: 60 mJ/pulse and 10 Hz (84.9 J/cm²); 80 mJ/pulse and 10 Hz (113.1 J/cm²). In a second study, the enamel surface and pulp chamber temperatures were evaluated during laser irradiations. All dyes produced enamel surface melting, with the exception of the caries indicator, and coal paste was the only dye that could be completely removed. All irradiation conditions produced temperature increases of up to 615.08°C on the enamel surface. Nd:YAG laser irradiation at 60 mJ/pulse, 10 Hz and 84.9 J/cm² promoted no harmful temperature increase in the pulp chamber (ANOVA, p < 0.05). Among all dyes tested, the coal paste was an efficient photoabsorber for Nd:YAG irradiation, considered feasible for clinical practice. Nd:YAG laser at 84.9 J/cm² can be indicated as a safe parameter for use in caries prevention.     

Ultrastructural analysis of the low level laser therapy effects on the lesioned anterior tibial muscle in the Gerbil

Low level laser therapy (LLLT) is known for its positive results but studies on the biological and biomodulator characteristics of the effects produced in the skeletal muscle are still lacking. In this study the effects of two laser dosages, 5 or 10 J/cm², on the lesioned tibial muscle were compared. Gerbils previously lesioned by 100 g load impact were divided into three groups: GI (n = 5) controls, lesion non-irradiated; GII (n = 5), lesion irradiated with 5 J/cm² and GIII (n = 5), lesion irradiated with 10 J/cm², and treated for 7 consecutive days with a laser He–Ne (λ = 633 nm). After intracardiac perfusion, the muscles were dissected and reduced to small fragments, post-fixed in 1% osmium tetroxide, dehydrated in increasing alcohol concentrations, treated with propylene oxide and embedded in Spurr resin at 60 °C. Ultrafine cuts examined on a transmission electron microscope (Jeol 1010) revealed in the control GI group a large number of altered muscle fibers with degenerating mitochondria, intercellular substance containing degenerating cell fragments and budding blood capillaries with underdeveloped endothelial cells. However, groups GII and GIII showed muscle fibers with few altered myofibrils, regularly contoured mitochondria, ample intermembrane spaces and dilated mitochondrial crests. The clean intercellular substance showed numerous collagen fibers and capillaries with multiple abluminal processes, intraluminal protrusions and several pinocytic vesicles in endothelial cells. It was concluded that laser dosages of 5 or 10 J/cm² delivered by laser He–Ne (λ = 633 nm) during 7 consecutive days increase mitochondrial activity in muscular fibers, activate fibroblasts and macrophages and stimulate angiogenesis, thus suggesting effectivity of laser therapy under these experimental conditions.     

Laser imprinting of 3D structures in gel-based titanium oxide organic-inorganic hybrids

First results on femtosecond laser 3D-microstructuring are reported in a novel class of organic-inorganic hybrid materials based on titanium oxide gels. Transparent optical-grade polished hybrid samples demonstrate strong photosensitivity assigned to electrons trapped as Ti³⁺ centers. Two different regimes of the microstructuring are observed: reversible and irreversible. In tight-focusing conditions using “on-the-fly” technique the single-pulse microstructuring is achieved with nanojoule laser pulses. The process thresholds have been studied on the surface and into the bulk of the material with irradiation by 1, 2, 10, and 100 laser pulses. A reduction of the damage threshold fluence by a factor of 2.5 is observed when increasing exposure from 1 pulse (1.2 J/cm²) to 100 pulses (0.5 J/cm²). PACS 42.62.-b; 40.70.-a; 78.66.Sq     

Processing of W/Si and Si/W bilayers and multilayers with single and multiple excimer-laser pulses

Interdiffusion phenomena, thermal damage and ablation of W/Si and Si/W bilayers and multilayers under XeCl-excimer laser (=308 nm) irradiation at fluences of 0.15, 0.3 and 0.6 J/cm² were studied. Samples were prepared by UHV e-beam evaporation onto oxidized Si. The thickness of W and Si layers and the total thickness of the structures were 1–20 nm and 40–100 nm, respectively. 1 to 300 laser pulses were directed to the same irradiation site. At 0.6 J/cm² the samples were damaged even by a single laser pulse. At 0.3 J/cm² WSi₂ silicide formation, surface roughening and ablation were observed. The threshold for significant changes depends on the number of pulses: it was between 3–10 pulses and 10–30 pulses for bilayers with W and Si surfaces, respectively, and more than 100 pulses for multilayers with the same total thickness of tungsten. At 0.15 J/cm² the periodicity of the multilayers was preserved. Temperature profiles in layered structures were obtained by numerical simulations. The observed differences of the resistance of various bilayers and multilayers against UV irradiation are discussed.     

Targeted destruction of murine macrophage cells with bioconjugated gold nanorods

Gold nanorods manifest a readily tunable longitudinal plasmon resonance with light and consequently have potential for use in photothermal therapeutics. Recent work by others has shown how gold nanoshells and rods can be used to target cancer cells, which can then be destroyed using relatively high power laser radiation (∼1×10⁵ to 1×10¹⁰ W/m²). Here we extend this concept to demonstrate how gold nanorods can be modified to bind to target macrophage cells, and show that high intensity laser radiation is not necessary, with even 5×10² W/m² being sufficient, provided that a total fluence of ∼30 J/cm² is delivered. We used the murine cell line RAW 264.7 and the monoclonal antibody CD11b, raised against murine macrophages, as our model system and a 5 mW solid state diode laser as our energy source. Exposure of the cells labeled with gold nanorods to a laser fluence of 30 J/cm² resulted in 81% cell death compared to only 0.9% in the control, non-labeled cells.     

Ultrasonic irradiation enhanced the efficacy of antimicrobial photodynamic therapy against methicillin-resistant Staphylococcus aureus biofilm

Antimicrobial photodynamic therapy (aPDT) is a non-pharmacological antimicrobial regimen based on light, photosensitizer and oxygen. It has become a potential method to inactivate multidrug-resistant bacteria. However, limited by the delivery of photosensitizer (PS) in biofilm, eradicating biofilm-associated infections by aPDT remains challenging. This study aimed to explore the feasibility of combining ultrasonic irradiation with aPDT to enhance the efficacy of aPDT against methicillin-resistant staphylococcus aureus (MRSA) biofilm. A cationic benzylidene cyclopentanone photosensitizer with much higher selectivity to bacterial cells than mammalian cells were applied at the concentration of 10 μM. 532 nm laser (40 mW/cm², 10 min) and 1 MHz ultrasound (500 mW/cm², 10 min, simultaneously with aPDT) were employed against MRSA biofilms in vitro. In addition to combined with ultrasonic irradiation and aPDT, MRSA biofilms were treated with laser irradiation only, photosensitizer only, ultrasonic irradiation only, ultrasonic irradiation and photosensitizer, and aPDT respectively. The antibacterial efficacy was determined by XTT assay, and the penetration depth of PS in biofilm was observed using a photoluminescence spectrometer and a confocal laser scanning microscopy (CLSM). In addition, the viability of human dermal fibroblasts (WS-1 cells) after the same treatments mentioned above and the uptake of P3 by WS-1 cells after ultrasonic irradiation were detected by CCK-8 and CLSM in vitro. Results showed that the percent decrease in metabolic activity resulting from the US + aPDT group (75.76%) was higher than the sum of the aPDT group (44.14%) and the US group (9.88%), suggesting synergistic effects. Meanwhile, the diffusion of PS in the biofilm of MRSA was significantly increased by 1 MHz ultrasonic irradiation. Ultrasonic irradiation neither induced the PS uptake by WS-1 cells nor reduced the viability of WS-1 cells. These results suggested that 1 MHz ultrasonic irradiation significantly enhanced the efficacy of aPDT against MRSA biofilm by increasing the penetration depth of PS. In addition, the antibacterial efficacy of aPDT can be enhanced by ultrasonic irradiation, the US + aPDT treatment demonstrated encouraging in vivo antibacterial efficacy (1.73 log₁₀ CFU/mL reduction). In conclusion, the combination of aPDT and 1 MHz ultrasound is a potential and promising strategy to eradicate biofilm-associated infections of MRSA.     

Tailored ablation processing of advanced biomedical hydroxyapatite by femtosecond laser pulses

The micromachining of hydroxyapatite (HAp) is highly important for orthopedics and dentistry, since human bone and teeth consist mainly of HAp. We demonstrate ultrashort Ti:sapphire laser ablation of HAp, using pulse-widths of 50 fs, 500 fs, and 2 ps at a wavelength of 820 nm and at 1 kpps. The crucial medical issue is to preserve the chemical properties of the machined (ablated) surface. If the chemical properties of HAp change, the human bone or tooth cannot re-grow after laser processing. Using X-ray photoelectron spectroscopy, we observe chemical properties of HAp ablated in air. The HAp is ablated at laser fluences of 3.2 J/cm² (6.4×10¹³ W/cm² at 50 fs), 3.3 J/cm² (6.6×10¹² W/cm² at 500 fs), and 9.6 J/cm² (4.8×10¹² W/cm² at 2 ps), respectively. As a result it is found that the ablated surface is unchanged after laser ablation over the pulse-width range used in this experiment. Received: 7 October 2002 / Accepted: 20 January 2003 / Published online: 28 May 2003 RID="*" ID="*"Corresponding author. Fax: +81-45/566-1533, E-mail: obara@obara.elec.keio.ac.jp     

Low-fluence CO2 laser irradiation decreases enamel solubility

This study investigated whether subablative-pulsed CO₂ laser (10.6 μm) irradiation, using fluences lower than 1 J/cm², was capable of reducing enamel acid solubility. Fifty-one samples of bovine dental enamel were divided into three groups: control group, which was not irradiated (CG); group laser A (LA) irradiated with 0.3 J/cm²; and group laser B (LB) irradiated with 0.7 J/cm². After irradiation, the samples were subjected to demineralization in an acetate buffer solution and were then analyzed by SEM. A finite-element model was used to calculate the temperature increase. The calcium and phosphorous content in the demineralization solution were measured with an ICP-OES. ANOVA and the t-test pairwise comparison (p < 0.016) revealed that LB showed significantly lower mean Ca and P content values in the demineralization solution than other groups. A reduction in the enamel solubility can be obtained with pulsed CO₂ laser irradiation (0.7 J/cm², 135 mJ/pulse, 74 Hz, 100 μs) without any surface photomodification and a less than 2°C temperature increase at a 3-mm depth from the surface.     

Investigation of laser irradiated poly- and monocrystalline aluminium by perturbed angular correlation measurements

Poly- and monocrystalline samples of aluminium implanted with ¹¹¹In to a dose of about 10¹³ at/cm² were irradiated at a temperature of 80 K with a Q-switched pulsed ruby laser. The energy density of the 25 ns pulses was in the range of 1–5 J/cm². Perturbed angular correlation measurements revealed the formation of several In-vacancy clusters, some of which give rise to electric field gradient tensors oriented along low-index crystallographic directions. This clearly shows that laser irradiation acts as a fast quench and that the monocrystalline structure is not destroyed, not even by the highest laser pulse intensity.     

Surface modulation of silicon surface by excimer laser at laser fluence below ablation threshold

Controlled single step fabrication of silicon conical surface modulations on [311] silicon surface is reported utilizing KrF excimer laser [λ=248 nm] at laser fluence below ablation threshold laser fluence. When laser fluence was increased gradually from 0 to 0.2 J/cm² for fixed 200 numbers of shots; first nanopores are observed to form at 0.1 J/cm², then very shallow nanocones evolve as a function of laser fluence. At 0.2 J/cm², nanoparticles are observed to form. Up to 0.15 J/cm² the very shallow nanocone volume is smaller but increases at a fast rate with laser fluence thereafter. It is observed that the net material volume before and after the laser irradiation remains the same, a sign of the melting and resolidification without any ablation.     

Tungsten silicide formation by XeCl excimer-laser irradiation of W/Si samples

We report a study of the formation of tungsten silicide at the W-Si interface, induced by multipulse (up to 300 shots) XeCl excimer-laser irradiation of W(150 nm)/Si and W(500 nm)/Si samples. Laser fluences ranging from 0.6 to 1.8 J/cm² were used. After laser treatment the samples were examined by different diagnostic techniques: Rutherford backscattering spectrometry, X-ray scattering, resistometry, and surface profilometry. Numerical computations of the evolution and depth profiles of the temperature in the samples as a consequence of a single 30 ns laser pulse were performed as well. The results indicate that it is possible to obtain a tungsten silicide layer at the W-Si interface at quite low fluences. The layer thickness increases with the number of laser pulses. Complete reaction of the 150 nm thick W film with silicon was obtained at the fluence of 1.2 J/cm² between 30 and 100 laser pulses and at 1.5 J/cm² after 30 laser pulses. The sheet resistance of these silicides was 5–10 . At the used fluences for the 500 nm thick W film only the onset of silicide synthesis at the W-Si interface was observed.     

488 nm连续激光晶化本征非晶硅薄膜的喇曼光谱研究

利用等离子增强化学气相沉积系统制备了本征非晶硅薄膜,并选用488 nm波长的连续激光进行晶化.采用喇曼测试技术对本征非晶硅薄膜在不同激光功率密度和扫描时间下的晶化状态进行了表征,并用514 nm波长与488 nm波长对样品的晶化效果进行了比较.测试结果显示:激光照射时间60 s, 激光功率密度在1.57×10⁵ W/cm²时,能实现非晶硅向多晶硅的转变,在功率密度达到2.7 56×10⁵ W/cm²时,有非晶开始向单晶转变,随着激光功率密度的继续增加,晶化结果仍为单晶;在功率密度为2.362×10⁵ W/cm²下,60 s照射时间晶化效果较好;在功率密度为2.756×10⁵ W/cm²和照射时间为60 s的条件下,用488 nm波长比514 nm波长的激光晶化本征非晶硅薄膜效果较好,并均为单晶态.     

Variety of nanostructures induced by femtosecond laser pulses on surface of Au/Cr film stack

Several nanostructures were obtained after irradiation with femtosecond laser pulse (130 fs, 800 nm, 1 kHz pulse repetition frequency) on Au/Cr film stack. The influence of laser parameters such as fluence (0.5 J/cm², 1.5 J/cm², 3 J/cm²) and the number of pulse were investigated. With single pulse irradiation, the nanoline and nonoparticle were obtained for the pulse fluence of 0.5 J/cm² and 3 J/cm², respectively. The formation mechanism of those nanostructures was discussed. The results of this experiment demonstrate that different kinds of nanostructures could be formed by varying the laser parameters such as fluence and the number of pulse.     

Femtosecond laser ablation of cemented carbides: properties and tribological applications

Laser ablation with fs laser pulses was performed in air on cobalt cemented tungsten carbide by means of a Ti : sapphire laser (800 nm, 100 fs). Small and moderate fluences (2, 5, 10 J/cm²) and up to 5×10⁴ pulses per irradiated spot were used to drill holes with aspect ratios up to 10. Cross-section cuts from laser-irradiated samples were produced and they were analysed with optical microscopy and SEM. EDX analyses were carried out on selected zones. Quasi-cylindrical holes were found for 2 J/cm², whereas for 5 and 10 J/cm² irregular shapes (lobes, bottoms wider than hole entrances) were found to occur after a given number of incident pulses. Layers with modified structure were evidenced at pore walls. SEM revealed a denser structure, while EDX analyses showed uniform and almost similar contents of W, C, and Co in these layers. As a direct application, patterning of coated WC-Co was carried out with 2 J/cm² and 100 pulses per pore. The resulted surfaces were tribologically tested and these tests revealed an improved friction and wear behaviour. PACS 42.65.Cs; 79.60.Ds     

Observation of X-ray spectra from nitrogen clusters irradiated with high-intensity ultrashort laser pulses

X-ray spectra from nitrogen clusters irradiated with ultrashort laser pulses are reported. The line spectra of H-like and He-like nitrogen ions have been observed by irradiation with 100 fs, 800 nm pulses at 7×10¹⁷ W/cm² irradiance. The generation of highly charged ions of N⁶⁺ and N⁷⁺ is explained by the optical field-induced ionization and the subsequent collisional ionizations in the clusters. The He-δline has anomalously high brightness compared to other He-like lines. It is ascribed to charge exchange, which preferentially populates the n=5 level of N⁵⁺. Received: 7 October 1999 / Published online: 23 February 2000     

Effects of laser irradiation energy density on the properties of pulsed laser deposited ITO thin films

The properties of indium tin oxide (ITO) thin films, deposited at room temperature by simultaneous pulsed laser deposition (PLD), and laser irradiation of the substrate are reported. The films were fabricated from different Sn-doped In₂O₃ pellets at an oxygen pressure of 10 mTorr. During growth, a laser beam with an energy density of 0, 40 or 70 mJ/cm² was directed at the middle part of the substrate, covering an area of ∼1 cm². The non-irradiated (0 mJ/cm²) films were amorphous; films irradiated with 40 mJ/cm² exhibited microcrystalline phases; and polycrystalline ITO films with a strong 〈111〉> preferred orientation was obtained for a laser irradiation density of 70 mJ/cm². The resistivity, carrier density, and Hall mobility of the ITO films were strongly dependent on the Sn doping concentration and the laser irradiation energy density. The smallest resistivity of ∼1×10^-4 Ω cm was achieved for a 5 wt % Sn doped ITO films grown with a substrate irradiation energy density of 70 mJ/cm². The carrier mobility diminished with increasing Sn doping concentration. Theoretical models show that the decrease in mobility with increasing Sn concentration is due to the scattering of electrons in the films by ionized centers. PACS 81.15.Fg; 73.61.-r; 73.50.-h     

表面层对1 064 nm高反射镜损伤阈值影响

 采用电子束蒸发的方法制备了３种具有不同表面层材料及结构的中心波长为1 064 nm的零度高反镜,３种膜系表面层分别为1/4波长光学厚度的HfO₂,1/2波长光学厚度的SiO₂,以及1/4波长光学厚度的SiO₂。光谱测试表明：三者在1 064 nm处均有较高的反射率（高于99.8%）,利用热透镜的方法测量得到３个膜系辐照激光正入射情况下,薄膜对光的吸收比例分别为3.0×10^-6,5.0×10^-6和6.5×10^-6,其损伤阈值分别为32.5,45.2和28.4 J/cm²。并在膜层内部电场分布和膜层材料物理特性的基础上分析了３种不同表面层膜系吸收和损伤阈值差别的原因。     

Improvedp/n junctions in Ge-doped GaAs grown by molecular beam epitaxy

The effects of single-pulse ruby laser irradiation have been investigated in Si samples with disorder layers located at a depth of 2000 Å from the crystal surface and extending up to 8000 Å. This disorder was obtained by implantation with 350 keV N⁺ to a fluence of 2×10¹⁶/cm². Channeling, diffraction and transmission electron microscopy were used to characterize the structure of the irradiated layers. After 1.5 J/cm² irradiation the damaged layer reorders partially, while for about 2.0J/cm² the surface single crystal becomes polycrystalline. At a higher energy density all the material undergoes the transition to single crystal. Calculations based on the liquid model accounts in part for the experimental results.