共查询到20条相似文献,搜索用时 515 毫秒
1.
Shazia Bashir M. Shahid Rafique Chandra S.R. Nathala Ali Ajami Wolfgang Husinsky 《辐射效应与固体损伤》2013,168(5):414-428
The effect of fluence and pulse duration on the growth of nanostructures on chromium (Cr) surfaces has been investigated upon irradiation of femtosecond (fs) laser pulses in a liquid confined environment of ethanol. In order to explore the effect of fluence, targets were exposed to 1000 pulses at various peak fluences ranging from 4.7 to 11.8?J?cm–2 for pulse duration of ~25?fs. In order to explore the effect of pulse duration, targets were exposed to fs laser pulses of various pulse durations ranging from 25 to 100?fs, for a constant fluence of 11.8?J?cm–2. Surface morphology and structural transformations have been analyzed by scanning electron microscopy and Raman spectroscopy, respectively. After laser irradiation, disordered sputtered surface with intense melting and cracking is obtained at the central ablated areas, which are augmented with increasing laser fluence due to enhanced thermal effects. At the peripheral ablated areas, where local fluence is approximately in the range of 1.4–4?mJ?cm–2, very well-defined laser-induced periodic surface structures (LIPSS) with periodicity ranging from 270 to 370?nm along with dot-like structures are formed. As far as the pulse duration is concerned, a significant effect on the surface modification of Cr has been revealed. In the central ablated areas, for the shortest pulse duration (25?fs), only melting has been observed. However, LIPSS with dot-like structures and droplets have been grown for longer pulse durations. The periodicity of LIPSS increases and density of dot-like structures decreases with increasing pulse duration. The chemical and structural modifications of irradiated Cr have been revealed by Raman spectroscopy. It confirms the formation of new bands of chromium oxides and enol complexes or Cr-carbonyl compounds. The peak intensities of identified bands are dependent upon laser fluence and pulse duration. 相似文献
2.
N. Takada T. Nakano K. Sasaki 《Applied Physics A: Materials Science & Processing》2010,101(2):255-258
It is well known that a crater is formed on the target surface by the irradiation of intense laser pulses in laser ablation.
In this work, we report that additional pits are formed on the bottom surface of the ablation crater due to the collapse of
a cavitation bubble in liquid-phase laser ablation. We observed the formation of several cavitation-induced pits when the
fluence of the laser pulse used for ablation was approximately 5 J/cm2. The number of cavitation-induced pits decreased with the laser fluence, and we observed one or two cavitation-induced pits
when the laser fluence was higher than 10 J/cm2. In addition, we examined the influence of the liquid temperature on the formation of cavitation-induced pits. The collapse
of the cavitation bubble was not observed when the liquid temperature was close to the boiling temperature, and in this case,
we found no cavitation-induced pits on the bottom surface of the ablation crater. This experimental result was discussed by
considering the cavitation parameter. 相似文献
3.
Shazia Bashir M. Shahid Rafique Ali Ajami Wolfgang Husinsky Umm-i-Kalsoom 《Applied Physics A: Materials Science & Processing》2013,113(3):673-681
The present work deals with growth of nanoscale periodic and dot-like structures on the surface of stainless steel (SS) by the irradiation of femtosecond laser pulses. For this purpose Ti: Sapphire femtosecond laser pulses (wavelength of 800 nm, pulse length of 25 fs and pulse repetition rate of 1 kHz) were employed in a dry (air) and liquid confined (deionized water and ethanol) environments. The targets were exposed to 1000 succeeding pulses for various fluences ranging from 50 to 150 mJ?cm?2. Nanoscale structures including ripples, and dots were observed by SEM analysis. The growth and dependence of structure-formation on the ambient environment and laser fluence in both central as well as peripheral ablated areas is systematically investigated. The development of nanostructures and nanoripples is correlated with structural analysis carried out by micro Raman spectroscopy. 相似文献
4.
2 to 2.5 mJ/cm2 when a 0.5 ps pulse is used instead of a 15 ns laser pulse. Measurements on liquid indium show a different behavior. With 15 ns
laser pulses the threshold fluence is lowered by a factor of ∼3 from 100 mJ/cm2 for solid indium to 30 mJ/cm2 for liquid indium. In contrast, measurements with 0.5 ps laser pulses do not show any change in the ablation threshold and
are independent of the phase of the metal at 2.5 mJ/cm2. This behavior could be explained by thermal diffusion and heat conduction during the laser pulse and demonstrates in an
independent way the energy lost into the material when long laser pulses are applied. Time-of-flight measurements to investigate
the underlying ablation mechanism show thermal behavior of the ablated indium atoms for both ps and ns ablation and can be
fitted to Maxwell-Boltzmann distributions.
Received: 2 December 1996/Accepted: 11 December 1996 相似文献
5.
D.V. Tran H.Y. Zheng Y.C. Lam V.M. Murukeshan J.C. Chai D.E. Hardt 《Optics and Lasers in Engineering》2005,43(9):977-986
The effect of sub-threshold pulses of circularly polarized Ti:sapphire femtosecond laser system on crystalline (1 0 0) silicon wafer was investigated. Surface damage morphologies were studied by irradiating the test silicon surface with pulses (peak fluence of 0.25 J/cm2) in succession. These pulses were below the single-pulse surface damage threshold. After the few initial pulses, the observed surface damage morphologies were found to be characterized by a minor phase change region and a major surface damage area at the center, corresponding to the well-known laser-induced periodic surface structure (LIPSS). Further increase in the number of pulses resulted in the formation of new surface morphologies with different features such as ablation, modification, and re-deposited materials. These features were reproducible and more distinguishable at higher number of pulses. 相似文献
6.
The effect of fluence level on the discoloration of marble surfaces after the removal of the encrustation by 355 nm laser pulses is comparatively studied. Considering the thermochemical reaction possibly occurring in the encrustation during laser irradiation, the mechanism responsible for the discoloration of the cleaned marble surface is analyzed. The reduction of iron oxides by graphite plays a key role in determining the final color of the cleaned marble surface. A two-dimensional laser ablative cleaning model including the reaction heat is applied to calculate the temperature distribution during laser heating. The kinetics of the thermochemical reaction is estimated based on the simulated temperature field. The occurrence of the thermochemical reaction is also verified indirectly with experiments. The marble surfaces before and after laser irradiation are characterized in terms of the chemical components through surface enhanced Raman spectroscopy. The surface color is measured with a chromameter using a 1976 CIE L*a*b* color system. The proposed mechanism is also applied to numerically analyze the severe discoloration of marble cleaned with laser pulses at 1064 nm. 相似文献
7.
J. Bonse S.M. Wiggins J. Solis 《Applied Physics A: Materials Science & Processing》2005,80(2):243-248
The structural transformation dynamics of single-crystalline indium phosphide (InP) irradiated with 150 fs laser pulses at 800 nm has been investigated by means of time-resolved reflectivity measurements covering a time window from 150 fs up to 500 ns. The results obtained show that for fluences above a threshold of 0.16 J/cm2 thermal melting of the material occurs on the timescale of 1–2 ps. The evolution of the reflectivity on a longer timescale reveals the reflectivity of the liquid phase and shows resolidification times typically around 10–30 ns after which an amorphous layer several tens of nanometers thick is formed on the surface. This amorphous layer significantly alters the optical properties of the surface and finally leads to a reduced ablation threshold for subsequent laser pulses. Single-pulse ablation at higher fluences (>0.23 J/cm2) is preceded by an ultrafast phase transition (non-thermal melting) occurring within 400 fs after the arrival of the pulse to the surface. PACS 79.20.Ds; 78.47.+p; 64.70.-p 相似文献
8.
The effect of XeCl laser irradiation on biocompatibility of polyethersulfone (PES) film surface was investigated. For this
purpose, the surface of PES film was irradiated with different number of pulses at different fluences. The treated surfaces
were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy
(SEM), atomic force microscopy (AFM) and contact angle measurements. The platelet adhesion and cell culture measurements were
done on the treated surface for investigation of the biocompatibility. It was shown that, irradiation of surface with 500
pulses at a fluence of 25 mJ/cm2 is the most optimal condition for improving the platelet adhesion on the PES surface with a XeCl laser. 相似文献
9.
The effectiveness of the laser induced backside wet etching (LIBWE) of fused silica produced by subpicosecond (600 fs) and nanosecond (30 ns) KrF excimer laser pulses (248 nm) was studied. Fused silica plates were the transparent targets, and naphthalene-methyl-methacrylate (c = 0.85, 1.71 M) and pyrene-acetone (c = 0.4 M) solutions were used as liquid absorbents. We did not observe etching using 600 fs laser pulses, in contrast with the experiments at 30 ns, where etched holes were found. The threshold fluences of the LIBWE at nanosecond pulses were found to be in the range of 360-450 mJ cm−2 depending on the liquid absorbers and their concentrations. On the basis of the earlier results the LIBWE procedure can be explain by the thermal heating of the quartz target and the high-pressure bubble formation in the liquid. According to the theories, these bubbles hit and damage the fused silica surface. The pressure on the irradiated quartz can be derived from the snapshots of the originating and expanding bubbles recorded by fast photographic setup. We found that the bubble pressure at 460 mJ cm−2 fluence value was independent of the pulse duration (600 fs and 30 ns) using pyrene-acetone solution, while using naphthalene-methyl-methacrylate solutions this pressure was 4, 5 times higher at 30 ns pulses than it was at 600 fs pulses. According to the earlier studies, this result refers to that the pressure should be sufficiently high to remove a thin layer from the quartz surface using pyrene-acetone solution. These facts show that the thermal and chemical phenomena in addition to the mechanical effects also play important role in the LIBWE procedure. 相似文献
10.
A numerical software has been developed to simulate heating, enthalpy-based phase changes and ablation of silicon during pulsed or continuous-wave laser irradiation. The unsteady heat transfer equation is solved by finite differences in two or three dimensions with full resolution of the thin liquid layer. An intelligent adaptive grid refinement and a semi-analytic treatment of the surface elements have been implemented to simulate laser cuts with lots of laser pulses in moderate computing time. The code has been successfully verified by comparisons with an analytic solution and with experimental data. Details of the mathematical model, the implementation in Matlab®and comparisons with experimental laser cuts are presented in this paper. 相似文献
11.
The experimental results on the effect of erbium laser pulses (300–400 ns long, 2.94 μm wavelength) on the water surface loaded
by a transparent sapphire plate 9.6 mm thick are presented. The laser pulse intensity was modulated with a period of 8.2 ns.
The behavior of the phase of the modulated part of the photoacoustic response under given experimental conditions differs
significantly from the case of irradiation of a free liquid surface [1, 2]. 相似文献
12.
The current work reports on the influence of the number of laser pulses on the morphological and photoluminescence properties of SrAl2O4:Eu2+,Dy3+ thin films prepared by the pulsed laser deposition (PLD) technique. Atomic force microscopy (AFM) was used to study the surface topography and morphology of the films. The AFM data showed that the film deposited using a higher number of laser pulses was packed with a uniform layer of coarse grains. In addition, the surface of this film was shown to be relatively rougher than the films deposited at a lower number of pulses. Photoluminescence (PL) data were collected using the Cary Eclipse fluorescence spectrophotometer equipped with a monochromatic xenon lamp. An intense green photoluminescence was observed at 517 nm from the films prepared using a higher number of laser pulses. Consistent with the PL data, the decay time of the film deposited using a higher number of pulses was characteristically longer than those of the other films. The effects of laser pulses on morphology, topography and photoluminescence intensity of the SrAl2O4:Eu2+,Dy3+ thin films are discussed. 相似文献
13.
N.E. Karatzas 《Optics Communications》2006,267(2):498-504
Calculations are presented for the first four (odd and even) harmonics of an 800 nm laser from a gold surface, with pulse widths ranging from 100 down to 14 fs. For peak laser intensities above 1 GW/cm2 the harmonics are enhanced because of a partial depletion of the initial electron states. At 1011 W/cm2 of peak laser intensity the calculated conversion efficiency for 2nd-harmonic generation is 3 × 10−9, while for the 5th-harmonic it is 10−10. The generated harmonic pulses are broadened and delayed relative to the laser pulse because of the finite relaxation times of the excited electronic states. The finite electron relaxation times cause also the broadening of the autocorrelations of the laser pulses obtained from surface harmonic generation by two time-delayed identical pulses. Comparison with recent experimental results shows that the response time of an autocorrelator using nonlinear optical processes in a gold surface is shorter than the electron relaxation times. This seems to indicate that for laser pulses shorter than ∼30 fs, the fast nonresonant channel for multiphoton excitation via continuum-continuum transitions in metals becomes important as the resonant channel becomes slow (relative to the laser pulse) and less efficient. 相似文献
14.
Ultrashort high-energy electron beams are generated by focusing fs Ti:sapphire laser pulses on a thin metal tape at normal incidence. At laser intensities above 1016 W/cm2 , the fs laser plasma ejects copious amounts of electrons in a direction parallel to the target surface. These electrons are directly detected by means of a backside illuminated X-ray CCD, and their energy spectrum is determined with an electrostatic analyzer. The electrons were observed for two laser polarization directions, parallel and perpendicular to the observation direction. At the maximum applied intensity of 2×1017 W/cm2, the energy distribution peaks at around 35 keV with a hot tail detectable up to about 300 keV. The number of electrons per shot at 35 keV is about 5×108 per sterad per keV. Quasi-monoenergetic electron pulses with a relative energy spread of 1% were produced by using a 50-m slit in the beam path after the analyzer. This approach offers great potential for time-resolved studies of plasma, liquid, and surface structures with atomic-scale spatial resolution. PACS 41.75.Fr; 52.38.Kd; 52.70.Nc 相似文献
15.
C. Tomas J.P. Girardeau-Montaut M. Afif M. Romand M. Charbonnier T.M. Duc 《Applied Physics A: Materials Science & Processing》1997,64(5):467-471
3+ :YAG laser with 5th harmonic generator, generating 16 ps duration pulses at 213 nm, with energies up to 0.5 mJ. Experimental results concerning
the action of laser pulses, as well as the effects of residual pressure on the cleanliness of the photocathodes surface are
presented and discussed. Influence of laser pulses and residual pressure on the work function of the metal are also investigated.
Received: 15 April 1996/Accepted: 5 November
1996 相似文献
16.
S. U. Campisano M. G. Grimaldi P. Baeri G. Foti E. Rimini 《Applied Physics A: Materials Science & Processing》1980,22(2):201-203
Ge samples implanted with 40 keV Pb at a fluence of 3×1015/cm2 were irradiated with ruby laser single pulses of 15ns duration. Reordering of the damaged layer occurs for energy density
irradiation above 0.6 J/cm2. The Pb atoms redistribute with a large component at the sample surface which is easily etched off. The remaining part of
Pb impurities is substitutionally located, and the concentration exceeds the solid solubility limit by three order of magnitude.
The formation of the metastable solution is explained in terms of a transient liquid layer produced during laser irradiation. 相似文献
17.
M. S. Rafique M. Khaleeq-ur-Rahman T. Firdos K. Aslam M. Shahbaz Anwar M. Imran H. Latif 《Laser Physics》2007,17(9):1138-1145
A pulsed Nd:YAG laser (10 mJ, 12 ns, 1064 nm) was employed to study the IR irradiation effects on metallic samples of cadmium. The laser was irradiated for 100, 200, and 300 shots under a vacuum ~10?3 Torr. The results were investigated using a Hi Tech S3000H Scanning Electron Microscope (SEM) and X’pert Pro PANalytical X-ray Diffractometer (XRD). The micrographs obtained from SEM reveal that the surface morphological changes have occurred in the form of a crater. The forward expansion of plasma into an ambient gas coupled with the recondensation of the target surface results in the formation of debris. Large temperature gradients produce variations in the thermal resistance that leads to the distributed shape of the heat-affected zone. The hydrodynamic effects are apparent with a liquid flow to form the recast material around the periphery of the laser focal area. The turbulent resolidified material is formed when surface asperities are accelerated away from the liquid surface during each laser pulse due to melting followed by the thermal expansion of the liquid. The positive feed back of the repeated pulses resulted in the form of ripples. Grains appear on the surface as evidence of heterogeneous nucleation. The confirmation of the formation of these structures has been done by X-ray Diffractometer (XRD). 相似文献
18.
19.
Growth characteristics and surface morphology of boron carbide films fabricated by ablating a B4C target in high vacuum with a traditional KrF excimer laser and a high brightness hybrid dye/excimer laser system emitting at the same wavelength while delivering 700 fs pulses are compared. The ultrashort pulse processing is highly effective. Energy densities between 0.25 and 2 J cm−2 result in apparent growth rates ranging from 0.017 to 0.085 nm/pulse. Ablation with nanosecond pulses of one order of magnitude higher energy densities yields smaller growth rates, the figures increase from 0.002 to 0.016 nm/pulse within the 2-14.3 J cm−2 fluence window. 2D thickness maps derived from variable angle spectroscopic ellipsometry reveal that, when ablating with sub-ps pulses, the spot size rather than the energy density determines both the deposition rate and the angular distribution of film material. Pulse shortening leads to significant improvement in surface morphology, as well. While droplets with number densities ranging from 1 × 104 to 7 × 104 mm−2 deteriorate the surface of the films deposited by the KrF excimer laser, sub-ps pulses produce practically droplet-free films. The absence of droplets has also a beneficial effect on the stoichiometry and homogeneity of the films fabricated by ultrashort pulses. 相似文献
20.
S. I. Ashitkov P. S. Komarov A. V. Ovchinnikov E. V. Struleva M. B. Agranat 《JETP Letters》2016,103(8):544-548
The destruction of liquid tin at the extremely high strain rate caused by femtosecond laser pulses has been studied. The ablation and cavitation thresholds, as well as tensile stresses responsible for the destruction of liquid tin at a strain rate of ~109 s–1, have been experimentally determined. 相似文献