共查询到20条相似文献,搜索用时 15 毫秒
1.
D. Margarone L. Láska S. Gammino E. Krouský M. Pfeifer M. Rosiñski J. Skála A. Velyhan 《Applied Surface Science》2008,254(9):2797-2803
Long pulse laser shots of the PALS iodine laser in Prague have been used to obtain metal target ablation at various experimental conditions. Attention is paid mainly to the dependencies of the crater diameter on the position of minimum laser-focus spot with regard to the target surface, by using different laser wavelengths and laser energies. Not only a single one, but two minima, independently of the wavelength, of the target irradiation angle and of the target material, were recorded. Significant asymmetries, ascribed to the non-linear effects of intense laser beam with pre-formed plasma, were found, too. Estimations of ejected mass per laser pulse are reported and used to calculate the efficiency of laser-driven loading. Results on metal target ablation and crater formation at high intensities (from 2 × 1013 to 3 × 1016 W/cm2) are presented and compared. Crater depth, crater diameter and etching yield are reported versus the laser energy, in order to evaluate the ablation threshold fluence. 相似文献
2.
S. Amoruso R. Bruzzese C. Pagano X. Wang 《Applied Physics A: Materials Science & Processing》2007,89(4):1017-1024
We present an experimental characterization describing the characteristics features of the plasma plume dynamics and material
removal efficiency during ultrashort, visible (527 nm, ≈300 fs) laser ablation of nickel in high vacuum. The spatio-temporal
structure and expansion dynamics of the laser ablation plasma plume are investigated by using both time-gated fast imaging
and optical emission spectroscopy. The spatio-temporal evolution of the ablation plume exhibits a layered structure which
changes with the laser pulse fluence F. At low laser fluences (F<0.5 J/cm2) the plume consists of two main populations: fast Ni atoms and slower Ni nanoparticles, with average velocities of ≈104 m/s for the atomic state and ≈102 m/s for the condensed state. At larger fluences (F>0.5 J/cm2), a third component of much faster atoms is observed to precede the main atomic plume component. These atoms can be ascribed
to the recombination of faster ions with electrons in the early stages of the plume evolution. A particularly interesting
feature of our analysis is that the study of the ablation efficiency as a function of the laser fluence indicates the existence
of an optimal fluence range (a maximum) for nanoparticles generation, and an increase of atomization at larger fluences.
PACS 52.50.-b; 52.38.Mf; 79.20.Ds; 81.07.-b 相似文献
3.
Csaba László Sajti Ramin Sattari Boris Chichkov Stephan Barcikowski 《Applied Physics A: Materials Science & Processing》2010,100(1):203-206
Ablation efficiency and influences of laser parameters on a material removal rate by a nanosecond laser irradiation of α-Al2O3 are studied in gas and liquid phases. The laser ablation in the air yields maximum material removal rate of 12 ng/pulse using
a 4.6-mJ pulse energy at 4-kHz repetition rate, compared to 88 ng/pulse in the water flow. Using a specific interpulse distance
and a laser repetition rate further increase material removal rate by factor of 3 and 65, respectively, owing to an optimized
lattice temperature and laser pulse interactions with the generated cavitation bubble. For the ablation in the air, these
parameters do not significantly affect the ablation efficiency. 相似文献
4.
The efficiency (mm3/(J pulse)) of laser ablation of paint was investigated with nanosecond pulsed Nd:YAG lasers (λ = 532 nm) as a function of the following laser beam parameters: pulse repetition rate (1-10,000 Hz), laser fluence (0.1-5 J/cm2) and pulse duration (5 ns and 100 ns). In our study, the best ablation efficiency (η ≅ 0.3 mm3/J) was obtained with the highest repetition rate (10 kHz) at the fluence F = 1.5 J/cm2. This ablation efficiency can be associated with heat accumulation at high repetition rate, which leads to the ablation threshold decrease. Despite the low thermal diffusivity and the low optical absorption of the paint (thermal confinement regime), the ablation threshold fluence was found to depend on the pulse duration. At high laser fluence, the ablation efficiency was lower for 5 ns pulse duration than for the one of 100 ns. This difference in efficiency is probably due to a high absorption of the laser beam by the ejected matter or the plasma at high laser intensity. Accumulation of particles at high repetition rate laser ablation and surface shielding was studied by high speed imaging. 相似文献
5.
Femtosecond laser micromilling of Si wafers 总被引:1,自引:0,他引:1
Femtosecond laser micromilling of silicon is investigated using a regeneratively amplified 775 nm Ti:Sapphire laser with a pulse duration of 150 fs operating at 1 kHz repetition rate. The morphological observation and topological analysis of craters fabricated by single-shot laser irradiation indicated that the material removal is thermal in nature and there are two distinct ablation regimes of low fluence and higher fluence with logarithmical relations between the ablation depth and the laser fluence. Crater patterns were categorized into four characteristic groups and their formation mechanisms were investigated. Femtosecond laser micromilling of pockets in silicon was performed. The effect of process parameters such as pulse energy, translation speed, and the number of passes on the material removal rate and the formation of cone-shaped microstructures were investigated. The results indicate that the microstructuring mechanism has a strong dependence on the polarization, the number of passes and laser fluence. The optimal laser fluence range for Si micromilling was found to be 2-8 J/cm2 and the milling efficiency attains its maximum between 10 and 20 J/cm2. 相似文献
6.
Computation of the processes of laser heating of carbon silicon carbide composite material (CSCCM) samples in air (to temperatures
above 2000°C for 1 s) by IR laser radiation with a wavelength of 1.3 μm and intensity of 3 kWcm−2 in the presence of screening ablation plume have been carried out using the KARAT code. A comparison of the simulation results
with the experimental dependences of spatial and temporal fields of sample temperatures made it possible to determine the
absorptivity of thematerial, energy loss in the ablation plume, and, correspondingly, its influence on the heating and ablation
of the material under study. 相似文献
7.
We report the influence of substrate temperature on femtosecond laser ablation of silicon, stainless steel, and glass. Remarkable decrease in surface roughness was observed under high substrate temperature for silicon and stainless steel. While the ablation efficiency of glass as a typical wide band-gap material is scarcely altered at 900 K, the efficiency for stainless steel as a conductor apparently increased about 20% accompanied to the elevation of substrate temperature from 300 to 900 K. Silicon wafer results in slight increase of the ablation efficiency with decreasing the ablation threshold. Considering that the melting temperature of glass is much lower than those of silicon and steel, the observations from this work suggests that the material ablation caused by the ultrafast laser irradiation could not be explained in term of only laser-induced thermal excitation. 相似文献
8.
N. G. Semaltianos W. Perrie P. French M. Sharp G. Dearden S. Logothetidis K. G. Watkins 《Applied Physics A: Materials Science & Processing》2009,94(4):999-1009
Femtosecond laser (180 fs, 775 nm, 1 kHz) ablation characteristics of the nickel-based superalloy C263 are investigated. The
single pulse ablation threshold is measured to be 0.26±0.03 J/cm2 and the incubation parameter ξ=0.72±0.03 by also measuring the dependence of ablation threshold on the number of laser pulses.
The ablation rate exhibits two logarithmic dependencies on fluence corresponding to ablation determined by the optical penetration
depth at fluences below ∼5 J/cm2 (for single pulse) and by the electron thermal diffusion length above that fluence. The central surface morphology of ablated
craters (dimples) with laser fluence and number of laser pulses shows the development of several kinds of periodic structures
(ripples) with different periodicities as well as the formation of resolidified material and holes at the centre of the ablated
crater at high fluences. The debris produced during ablation consists of crystalline C263 oxidized nanoparticles with diameters
of ∼2–20 nm (for F=9.6 J/cm2). The mechanisms involved in femtosecond laser microprocessing of the superalloy C263 as well as in the synthesis of C263
nanoparticles are elucidated and discussed in terms of the properties of the material. 相似文献
9.
We investigated the mechanisms of material ejection in Q-switched Er:YAG laser tissue ablation (70-ns pulse duration) where moderate and large radiant exposures are associated with large volumetric energy densities in the target material. For water, an initial phase of non-equilibrium surface vaporization is followed by an explosive vaporization of the superficial liquid volume from a supercritical state. The ablation of deeper layers with lower peak temperatures proceeds as phase explosion. For mechanically strong tissues, non-equilibrium surface vaporization is followed by a vapour explosion coupled with thermal dissociation of the biomolecules into volatile products. In deeper layers, ablation proceeds as confined boiling with mechanical tearing of the tissue matrix by the vapour pressure. The recoil stress induced at a radiant exposure of 5.4 J/cm2 is in the order of 500–900 MPa. For water and soft tissues such as liver, the recoil causes a powerful secondary material expulsion. For stronger tissues such as skin, no secondary expulsion was observed even though the recoil stress largely exceeds the static tensile strength of the tissue. Recoil-induced material expulsion results in an increase of both ablation efficiency and mechanical side effects of ablation. Theoretical modelling of the succession of phase transitions in nanosecond-laser tissue ablation and of recoil-induced material expulsion remain a major challenge for future work. PACS 42.62.Be; 79.20.Ds 相似文献
10.
2 laser using a miniature water spray is demonstrated. An ablation threshold of 1.4 J/cm2, an optimal energy density of 9–10 J/cm2, and a corresponding specific ablation energy of 25–30 J/mm3 are found for pig thighbone compacta at λ=9.57 μm and a beam waist diameter of 0.5 mm. The water spray alleviates tissue
carbonization even at high laser pulse repetition rates and increases ablation efficiency.
Received: 9 March 1998/Revised version: 6 July 1998 相似文献
11.
The use of ultrashort laser pulses is a way to increase recoil momentum under laser ablation of materials, because, in this case, the energy deposition per unit volume of the target material is substantially higher due to reduced heat dissipation. By using methods of combined interferometry, we estimated the specific impulse (~200–900 s), momentum coupling coefficient (~2 × 10?5?3 × 10?4 Ns/J), laser-energy conversion efficiency to kinetic energy of the gas-plasma flow (~0.05–0.82), and degree of the gas-plasma flow monochromaticity (~0.72–0.92) under femtosecond (τ ~ 45 fs, λ ~ 800 nm) ablation of refractory metals (Ti, Zr, Mo, and Nb) in vacuum. 相似文献
12.
A method to generate a pulse sound source for acoustic tests based on nanosecond laser ablation with a plasma plume is discussed. Irradiating a solid surface with a laser beam expands a high-temperature plasma plume composed of free electrons, ionized atoms, etc. at a high velocity throughout ambient air. The shockwave generated by the plasma plume becomes the pulse sound source. A laser ablation sound source has two features. Because laser ablation is induced when the laser fluence reaches 1012–1014 W/m2, which is less than that for laser-induced breakdown (1015 W/m2), laser ablation can generate a lower sound pressure, and the sound source has a hemispherical radiation pattern on the surface where laser ablation is generated. Additionally, another feature is that laser-induced breakdown sound sources can fluctuate, whereas laser ablation sound sources do not because laser ablation is produced at a laser beam–irradiation point. We validate this laser ablation method for acoustic tests by comparing the measured and theoretical resonant frequencies of an impedance tube. 相似文献
13.
R. Torres M. Jadraque M. Martin 《Applied Physics A: Materials Science & Processing》2005,80(8):1671-1675
Neutral silicon cluster formation in the laser (308 nm) ablation of silicon monoxide was investigated through the analysis of composition and dynamics of the ablation plume under different laser fluence conditions. The neutral species were ionized by a second laser (193 nm) and the positionized species detected by TOF-MS (time-of-flight mass spectrometry). At low laser fluences, plume composition is dominated by SiO; above 0.6 J/cm2 Si, SiO and Si2 have comparable intensity and Sin (n≤7) clusters are observed. Flow velocities and temperatures of the ejected species are nearly mass-independent, indicating that the plume dynamics are close to the strong expansion limit, implying a collisional regime. Through the relation between the estimated values of terminal flow velocity and surface temperature, uT2∝TS, it is found that, at low laser fluences, the surface temperature increases linearly with laser fluence, whereas, at the laser fluence at which Sin clusters are observed, the increase of temperature is below the linear dependence. The population distribution of the ejected Sin provides some indication of a formation mechanism based on condensation. Analogies between the ablation behavior of silicon monoxide and silicon targets are considered. PACS 82.30.Nr; 81.05.Gc; 78.70.-g 相似文献
14.
Ablation of organic polymers is described on the basis of photothermal bond breaking within the bulk material. Here, we assume
a first-order chemical reaction, which can be described by an Arrhenius law. Ablation starts when the density of broken bonds
at the surface reaches a certain critical value.
In order to understand the ablation behavior near the threshold fluence, φth, non-stationary regimes must be considered. The present treatment reveals several qualitative differences with respect to models that treat
ablation as a surface process: (i) Ablation starts sharply with a front velocity that has its maximum value just after the onset. (ii) The transition
to the quasi-stationary ablation regime is faster. (iii) Near threshold, the ablated depth h has a square-root dependence
on laser fluence, i.e., h∝(φ-φth)1/2. The ablation velocity is very high even near φth. (iv) With φ≈φth ablation starts well after the laser pulse. (v) The depletion of species is responsible for the Arrhenius tail observed with
fluences φ≤φth. (vi) Residual modification of material has maximum near the threshold. (vii) Stationary regimes of ablation demonstrate change of effective activation energy with laser intensity.
The model calculations are applied to Polyimide (KaptonTM H). Here, differences in single-pulse ablated depth determined from mass loss and profilometry should be about 10 nm.
Received: 16 February 1999 / Accepted: 18 February 1999 / Published online: 28 April 1999 相似文献
15.
E. Yu. Loktionov A. V. Ovchinnikov Yu. Yu. Protasov D. S. Sitnikov 《Journal of Applied Spectroscopy》2010,77(4):561-568
We present the results of an experimental study of the ablation energy thresholds and ablated mass for a number of refractory
metals (Ti, Zr, Nb, Mo) by femtosecond (τ
0.5 = 45–70 fs) exposed to laser pulses in the ultraviolet — near infrared range (λ = 266, 400, 800 nm) under atmospheric conditions and under vacuum (p ~ 10–2 Pa). We have analyzed the ablation efficiency (mass yield per unit energy of the acting coherent radiation) and ablation
energy thresholds vs. the laser pulse duration and photon energy. 相似文献
16.
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
17.
Laser performance of resonantly-pumped Er3+-doped Y2O3 ceramic laser for remote DIAL CO2 monitoring is reported. Slope efficiency of 64.6% and output power of over 9.3 W have been achieved with this eyesafe, 1.6-μm, CW laser in a cryogenically cooled operation regime despite the marginal optical quality of currently available laser gain material. 相似文献
18.
The dependence of the ablation rate of aluminium on the fluence of nanosecond laser pulses with wavelengths of 532 nm and
respectively 1064 nm is investigated in atmospheric air. The fluence of the pulses is varied by changing the diameter of the
irradiated area at the target surface, and the wavelength is varied by using the fundamental and the second harmonic of a
Q-switched Nd-YAG laser system. The results indicate an approximately logarithmic increase of the ablation rate with the fluence
for ablation rates smaller than ∼6 μm/pulse at 532 nm, and 0.3 μm/pulse at 1064 nm wavelength. The significantly smaller ablation rate at 1064 nm is due to the small optical absorptivity,
the strong oxidation of the aluminium target, and to the strong attenuation of the pulses into the plasma plume at this wavelength.
A jump of the ablation rate is observed at the fluence threshold value, which is ∼50 J/cm2 for the second harmonic, and ∼15 J/cm2 for the fundamental pulses. Further increasing the fluence leads to a steep increase of the ablation rate at both wavelengths,
the increase of the ablation rate being approximately exponential in the case of visible pulses. The jump of the ablation
rate at the threshold fluence value is due to the transition from a normal vaporization regime to a phase explosion regime,
and to the change of the dimensionality of the hydrodynamics of the plasma-plume.
相似文献
19.
J. Jandeleit G. Urbasch H. D. Hoffmann H. -G. Treusch E. W. Kreutz 《Applied Physics A: Materials Science & Processing》1996,63(2):117-121
The ablation process of thin copper films on fused silica by picosecond laser pulses is investigated. The ablation area is characterized using optical and scanning electron microscopy. The single-shot ablation threshold fluence for 40 ps laser pulses at 1053 nm has been determinated toF
thres = 172 mJ/cm2. The ablation rate per pulse is measured as a function of intensity in the range of 5 × 109 to 2 × 1011 W/cm2 and changes from 80 to 250 nm with increasing intensity. The experimental ablation rate per pulse is compared to heat-flow calculations based on the two-temperature model for ultrafast laser heating. Possible applications of picosecond laser radiation for microstructuring of different materials are discussed. 相似文献
20.
The generation of lower (third) and higher harmonics of femtosecond laser radiation in plasmas produced by laser ablation
of different targets with a small atomic number Z (B, Be, Li) has been investigated. The high (10−3) efficiency of third-harmonic generation was observed in plasma produced on the boron surface. Efficient third-harmonic generation
was also observed in beryllium plasma using femtosecond pulses of Ti:sapphire laser radiation (λ = 790 nm) and its second
harmonic (395 nm). We could tune the higher harmonics generation spectrum by tuning the crystal converter when using 395-nm
radiation to be converted. It is shown that, in plasmas formed on targets with small Z, the conversion efficiency and limiting generated harmonic order depend on the delay between the ablation pulse and the pulse
to be converted. 相似文献