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1.
This paper presents the surface microstructure of Ti and Ti6Al4V alloy irradiated with a high output energy XeCl ( = 308 nm) excimer laser. The treatments are carried out on both materials at two beam fluences and the effects of single- and multiple-pulse irradiation are compared. The results of the scanning electron microscopy and of the X-ray diffraction techniques suggest the possible influence of both time-behaviour and energy fluence of the laser pulse on the relative weight of the ablation rate and of the reaction product deposition rate at the sample surface.  相似文献   

2.
Rhodamine 6G has been dissolved in copolymers of 2-HydroxyEthyl MethAcrylate (HEMA) and Methyl MethAcrylate (MMA) and the resulting solid-state solutions have been pumped at 337 nm and 532 nm. Lasing efficiencies similar to those found in ethanol solution have been obtained with a 1:1 vol/vol HEMA: MMA copolymer matrix, and lifetimes of ca. 10 000 (337 nm pumping) and ca. 75 000 (532 nm pumping) pulses at repetition rates up to 15 Hz and 10 Hz, respectively, have been demonstrated.  相似文献   

3.
We have studied the ablation of an aqueous CuCl2 solution in a pulsed Nd:YAG laser field featuring a speckle-patterned structure characterized by spatial radiation energy fluence fluctuations. This leads to a nonuniform distribution of the energy absorbed in the bulk of the sample being irradiated and causes local overheating centers to form, wherein ablation is observed to take place at laser energy fluences below the threshold value found in experiments with a homogeneous laser beam. This effect should be manifest in the laser irradiation of biotissues which, as a rule, scatter light strongly.  相似文献   

4.
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.  相似文献   

5.
Clean ablation of poly(tetrafluoroethylene) (PTFE) at etch rates in excess of 7µm/pulse has been achieved with an excimer laser using 308nm radiation and a 25 ns pulse width. This was accomplished by doping the ultraviolet-transparent PTFE polymer with polyimide. Ablation rates were investigated as a function of fluence in the range from 1 to 12J/cm2 and dopant levels up to 15% (wt/wt). Results show that at a given fluence there exists an optimum absorption coefficient max, for which maximum ablation rates are achieved. The value of max was found to decrease with increasing fluence. The relationship between max and fluence was determined from existing ablation rate models and found to compare favorably with empirical results.  相似文献   

6.
We report on the laser action of modified dipyrromethene.BF2 complexes both dissolved in poly(methyl methacrylate) and copolymerized with methyl methacrylate. All recently synthesized dyes have the chromophore core of laser dye pyrromethene 567, differing in the substituent in position 8. The new dyes showed important and most significant increases in both lasing efficiency and photostability. When the laser samples were pumped transversely at 534 nm, laser emission was obtained with efficiencies of over 30% in most cases, to be compared with a lasing efficiency of 12% exhibited by reference dye pyrromethene 567 under the same experimental conditions. Some of the materials exhibited highly photostable laser action, with no sign of degradation in the laser output after 60000 pump pulses at the same position of the sample at a repetition rate of 10 Hz, whereas the laser emission of reference dye pyrromethene 567 dropped to zero after less than 40000 pump pulses. Received: 19 November 2002 / Revised version: 20 February 2003 / Published online: 9 April 2003 RID="*" ID="*"Corresponding author. Fax: +34-91/564-2431, E-mail: acostela@iqfr.csic.es  相似文献   

7.
Absolutely calibrated emission spectroscopy has been used to determine the particle number densities of XeCl*(B), XeCl*(C), and Xe2Cl* in a small scale Ne/Xe/HCl discharge with well-defined current and voltage pulses for a wide range of parameters. The measured particle number densities could be reproduced quite well by numerical model calculations using the rate-coefficient values of Quiñones et al. [1] for the quenching of XeCl*(B,C) by Ne, Xe, and 2Xe, but 3.0 × 10–31 cm6/s for the formation of Xe2Cl* by (Ne + Xe)-quenching. For the electron quenching, we recommend a rate coefficient value of 3.2 × 10–8 cm3/s. From the equilibrium ratio of the particle number densities of XeCl*(C) and XeCl*(B), the energy separation between these states has been estimated to be 72 ± 33 cm–1 with the B state placed above the C state.  相似文献   

8.
The first observation of fullerene C60 ultraviolet photolysis in hexane solution was published two years ago [1]. Similar further experiments realized with an ultraviolet lamp and solar light gave inconsistent results with ambiguous interpretations. We report the unexpectedly fast and efficient degradation of the fullerenes in n-hexane solutions, induced by an XeCl-excimer laser. Well-defined experimental conditions and good reproducibility in these experiments allow us to estimate the minimal value of the quantum yield of fullerene photolysis.  相似文献   

9.
Due to the growing demand for high-current and long-duration electron-beam devices, laser electron sources were investigated in our laboratory. Experiments on electron-beam generation and propagation from aluminium and copper targets illuminated by XeCl (308 nm) and KrCl (222 nm) excimer lasers, were carried out under plasma ignition due to laser irradiation. This plasma supplied a spontaneous accelerating electric field of about 370 kV/m without an external accelerating voltage. By applying the modified one-dimensional Poisson equation, we computed the expected current and we also estimated the plasma concentration during the accelerating process. At 40 kV of accelerating voltage, an output current pulse of about 80 A/cm2 was detected from an Al target irradiated by the shorter wavelength laser.On leave from Institute of General Physics, Moscow, Russia  相似文献   

10.
The generation mechanism and thermal stability of high carrier concentrations in GaAs formed by KrF-excimer-laser doping with Si using SiH4 gas are investigated. The channeling Particle-Induced X-ray Emission (PIXE) analysis reveals that a high substitutional fraction of over 90% and preferential replacement of Si atoms on Ga sites result in the generation of carrier concentrations as high as 5×1019 cm–3. In addition, the thermal stability of the doped regions is studied. The high carrier concentrations in a nonthermal equilibrium state return to a thermal equilibrium state by postannealing.Presented at LASERION'93, Munich, June 21–23, 1993  相似文献   

11.
We have investigated the interface mixing of Ni2O3/SiO2, NiO/SiO2, and Ni/SiO2 induced by the irradiation with Ar, Kr and Xe ions of energies ranging from 90 MeV to 260 MeV. Since these energies are in the electronic stopping regime, atomic transport processes will not be directly initiated by elastic ion–target collisions, but need to be excited by secondary processes like electron–phonon coupling or Coulomb explosion. Nevertheless, we have observed a strong mixing effect in the ceramic systems if the electronic energy loss exceeds a certain threshold value. Estimation of an effective diffusion constant indicates that diffusion takes place in the molten ion track. In contrast to the ceramics, the metallic Ni layer is still insensitive even for the highest electronic stopping power used (Se=28 keV/nm) and does not exhibit mixing with its SiO2 substrate. In addition, NiO/SiO2 and Ni/SiO2 were irradiated in the nuclear stopping regime with 600 keV Kr and 900 keV Xe–ions. Here the intermixing effect is in good agreement with the assumption of ballistic atomic transport. Received: 5 February 2002 / Accepted: 11 February 2002 / Published online: 3 May 2002 RID="*" ID="*"Corresponding author. Fax: +49-711/685-3866, E-mail: bolse@ifs.physik.uni-stuttgart.de  相似文献   

12.
Here we report on experimental studies of femtosecond laser induced surface metal alloying. We demonstrate that layers of different metals can be mixed in a certain range of laser pulse energies. Numeric simulations demonstrate that the sub-surface melting and mixing is advantaged through the difference in the electron-phonon coupling constants of the metals in the multi-layer system. Dependence of the depth of the mixed layer on the number of laser pulses per unit area is studied. Numeric simulations illustrate physical picture of the laser alloying process.  相似文献   

13.
We investigate the TEA CO2 laser ablation of films of poly(methyl methacrylate), PMMA, with average MW 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 CaF2 substrates were irradiated with a pulsed CO2 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/cm2. 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 MW 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 MW and filaments are observed to be ejected out of the irradiated volume in the samples made with high MW polymer. The implications of these results for the mechanisms of polymer IR laser ablation are discussed and compared with UV range studies.  相似文献   

14.
Absorptance losses in MgF2, CaF2 and BaF2 during 193-nm (DUV) and 157-nm (VUV) irradiation are investigated by employing a high-resolution laser calorimetric technique which allows the determination of both single- and two-photon absorptance at energy densities up to 110 mJ/cm2. A strong wavelength dependence of the DUV and VUV absorption characteristics is observed: while effective two-photon absorption takes place at 193 nm, either no similar effect at all (in the case of BaF2) or only a very minor effect (CaF2) is observed at 157 nm. A first explanation for this absorption behaviour is given, implying the energetic band structure of CaF2. In addition it is shown that, due to the strong nonlinear dependency, above a critical energy density the absorptance at 193 nm can exceed the absorptance at 157 nm. Furthermore, different single- and two-photon absorption coefficients are determined for different CaF2 samples at 193 nm, indicating a two-step absorption mechanism. In addition, laser-induced aging is found in a MgF2 sample at 193 nm, but not at 157 nm. Received: 21 June 2001 / Revised version: 2 November 2001 / Published online: 7 February 2002  相似文献   

15.
Thin films of Sb, Se and Sb2Se3 are deposited onto glass and irradiated by a cw-Ar+ laser beam. The kinetics of crystallization and oxidation are traced via the time dependence of optical reflectivity and temperature, T, of the irradiated zone. For Sb2Se3, transformations start abruptly when T attains a critical value, T c, independently of the laser beam power. These T c values are comparable to the ones observed under furnace annealing conditions.  相似文献   

16.
308nm准分子激光对C60薄膜的刻蚀特性研究   总被引:2,自引:0,他引:2  
宁东  楼祺洪 《光学学报》1995,15(7):09-912
测量在空气和真空中308nm准分子激光对C60薄膜的刻蚀速率和刻蚀阈值,讨论了环境中氧气对刻蚀特性的影响。  相似文献   

17.
The optical reflectivity (both specular and off-specular) of poly(methyl methacrylate) (PMMA) implanted with silicon ions (Si+) at energy of 50 keV, is studied in the spectral range 0.25-25 μm. The effect from the Si+ implantation on the reflectivity of two PMMA materials is examined in the dose range from 1014 to 1017 ions/cm2 and is linked to the structure formed in this ion implanted plastic. As compared to the pristine PMMA, an enhancement of the reflectivity of Si+ implanted PMMA is observed, that is attributed to the modification of the subsurface region of PMMA upon the ion implantation. The ion-produced subsurface organic interface is also probed by laser-induced thermo-lens.  相似文献   

18.
It is demonstrated that prolonged treatment in a constant magnetic field considerably increases the creep rate under compression of poly(methyl methacrylate) samples irradiated with gamma-ray doses as high as 100 kGy. For higher irradiation doses, the effect of the magnetic field on the creep rate is insignificant.  相似文献   

19.
The molecular dynamics in thin films (18 nm-137 nm) of isotactic poly(methyl methacrylate) (i-PMMA) of two molecular weights embedded between aluminium electrodes are measured by means of dielectric spectroscopy in the frequency range from 50 mHz to 10 MHz at temperatures between 273 K and 392 K. The observed dynamics is characterized by two relaxation processes: the dynamic glass transition (α-relaxation) and a (local) secondary β-relaxation. While the latter does not depend on the dimensions of the sample, the dynamic glass transition becomes faster (≤2 decades) with decreasing film thickness. This results in a shift of the glass transition temperature T g to lower values compared to the bulk. With decreasing film thickness a broadening of the relaxation time distribution and a decrease of the dielectric strength is observed for the α-relaxation. This enables to deduce a model based on immobilized boundary layers and on a region displaying a dynamics faster than in the bulk. Additionally, T g was determined by temperature-dependent ellipsometric measurements of the thickness of films prepared on silica. These measurements yield a gradual increase of T g with decreasing film thickness. The findings concerning the different thickness dependences of T g are explained by changes of the interaction between the polymer and the substrates. A quantitative analysis of the T g shifts incorporates recently developed models to describe the glass transition in thin polymer films. Received 12 August 2001 and Received in final form 16 November 2001  相似文献   

20.
RE, Mn:YAP (RE=Yb and Ce) crystals with dimension of Φ 25×60 mm were successfully grown by the Czochralski method. The spectroscopic properties of RE, Mn:YAP (RE=Yb and Ce) crystals before and after γ-irradiation were investigated at room temperature. The results show that the content of Mn4+ ions was increased with the Yb3+ ions co-doping, but decreased by Ce3+ ions co-doping. Thermoluminescence (TL) spectra of the crystals indicate three steps of recombination, and the probable recombination processes were discussed.  相似文献   

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