共查询到20条相似文献,搜索用时 31 毫秒
1.
K. Obata K. Sugioka T. Akane N. Aoki K. Toyoda K. Midorikawa 《Applied Physics A: Materials Science & Processing》2001,73(6):755-759
A collinear irradiation system of F2 and KrF excimer lasers for high-quality and high-efficiency ablation of hard materials by the F2 and KrF excimer lasers’ multi-wavelength excitation process has been developed. This system achieves well-defined micropatterning
of fused silica with little thermal influence and little debris deposition. In addition, the dependence of ablation rate on
various conditions such as laser fluence, irradiation timing of each laser beam, and pulse number is examined to investigate
the role of the F2 laser in this process. The multi-wavelength excitation effect is strongly affected by the irradiation timing, and an extremely
high ablation rate of over 30 nm/pulse is obtained between -10 ns and 10 ns of the delay time of F2 laser irradiation. The KrF excimer laser ablation threshold decreases and its effective absorption coefficient increases
with increasing F2 laser fluence. Moreover, the ablation rate shows a linear increase with the logarithm of KrF excimer laser fluence when the
F2 laser is simultaneously irradiated, while single KrF excimer laser ablation shows a nonlinear increase. The ablation mechanism
is discussed based on these results.
Received: 16 July 2001 / Accepted: 27 July 2001 / Published online: 2 October 2001 相似文献
2.
Theoretical studies of ultrafast ablation of metal targets dominated by phase explosion 总被引:2,自引:0,他引:2
Ultrashort pulse laser ablation of metallic targets is investigated theoretically through establishing a modified two-temperature
model that takes into account both the temperature dependent electron–lattice coupling and the electron–electron-collision
dominated electron diffusion processes for higher electron temperature regime. The electron–lattice energy coupling rate is
found to reduce only slowly with increasing pulse duration, but grow rapidly with laser fluence, implying that the melting
time of metallic materials decreases as the laser intensity increases. By taking phase explosion as the primary ablation mechanism,
the predicted dependences of ablation rates on laser energy fluences for different laser pulse widths match very well with
the experimental data. It is also found that during phase explosion the ablation rate is almost independent of the pulse width,
whereas the ablation threshold fluence increases with the pulse duration even for femtosecond pulses. These theoretical results
should be useful in having proper understanding of the ablation physics of ultrafast micromachining of metal targets.
PACS 52.50.Jm; 61.80.Az; 72.15.Cz; 79.20.Ap; 79.20.Ds 相似文献
3.
L. Englert M. Wollenhaupt L. Haag C. Sarpe-Tudoran B. Rethfeld T. Baumert 《Applied Physics A: Materials Science & Processing》2008,92(4):749-753
Laser material processing of dielectrics with temporally asymmetric femtosecond laser pulses of identical fluence, spectrum,
and statistical pulse duration is investigated experimentally. To that end single shot structures at the surface of fused
silica as a function of fluence and pulse shape are analyzed with the help of scanning electron microscopy. Structures for
the bandwidth limited pulses show the known expansion in structure size with increasing laser fluence approaching the diffraction
limit, which is 1.4 μm for the 0.5NA microscope objective used. In contrast, structures from the asymmetric pulses are remarkably
stable with respect to variations in laser fluence and stay below 300 nm despite doubling the fluence. Different thresholds
for surface material modification with respect to an asymmetric pulse and its time reversed counterpart are attributed to
control of different ionization processes. 相似文献
4.
Q. Wang L. D. Chen X. J. Liu W. D. Yu X. M. Li 《Applied Physics A: Materials Science & Processing》2009,96(3):643-653
Melting, vaporization and resolidification processes of thin gold film irradiated by a femtosecond pulse laser are studied
numerically. The nonequilibrium heat transfer in electrons and lattice is described using a two-temperature model. The solid–liquid
interfacial velocity, as well as elevated melting temperature and depressed solidification temperature, is obtained by considering
the interfacial energy balance and nucleation dynamics. An iterative procedure based on energy balance and gas kinetics law
to track the location of liquid–vapor interface is utilized to obtain the material removal by vaporization. The effect of
surface heat loss by thermal radiation was discussed. The influences of laser fluence and duration on the evaporation process
are studied. Results show that higher laser fluence and shorter laser pulse width lead to higher interfacial temperature,
deeper melting and ablation depths. 相似文献
5.
Channels are traditionally machined in materials by drilling from the front side into the bulk. The processing rate can be
increased by two orders of magnitude for transparent materials by growing the channel from the rear side. The process is demonstrated
using nanosecond laser pulses to drill millimeter-sized channels through thick silica windows. Absorbing defects are introduced
onto the rear surface to initiate the coupling of energy into the material. Laser drilling then takes place when the fluence
exceeds a threshold. The drilling rate increases linearly with fluence above this threshold. While UV light drills about four
times faster than IR light, the pulse length (in the nanosecond regime) and the pulse repetition rate (in the 0.1–10 Hz range)
do not greatly influence the drilling rate per pulse.
Drilling rates in excess of 100 μm per pulse are achieved by taking advantage of the propagation characteristics of the plasma
created at the drilling front. The plasma during rear-side drilling generates a laser-supported detonation wave into the bulk
material. The geometry also seems to increase the efficiency of the laser-induced plasma combustion and shock wave during
the pulse by confining it in front of the channel tip.
Received: 1 July 1999 / Accepted: 17 April 2000 / Published online: 20 September 2000 相似文献
6.
J. Cheng W. Perrie M. Sharp S. P. Edwardson N. G. Semaltianos G. Dearden K. G. Watkins 《Applied Physics A: Materials Science & Processing》2009,95(3):739-746
Picosecond laser single pulse ablation of Au, Al and Ti alloy (Ti6Al4V) was experimentally investigated with a laser pulse
width of 10 ps at a wavelength of 1064 nm for potential industrial micromachining applications. The diameters, depths and
morphologies of the drilled craters were studied. Two novel phenomena were found: as hole diameters decreased with fluence,
a change of slope of the trend line indicated a change in ablation mechanism for Al and Ti alloy, metallic materials with
short electron-phonon coupling times (<10 ps), while Au showed no such transition: an isolated island structure was also observed
on Au due to significant melt expulsion. A one-dimensional two-temperature model has been used to discriminate different ablation
phenomena. It is shown that metallic materials with different electron–phonon coupling constant have different ablation characteristics
in the ps regime. This study could be very helpful for metallic material micromachining with high repetition rate ps lasers
pulses which indicates that high throughput may be achieved as well as good machining quality. 相似文献
7.
Effect of Pulse Width and Fluence of Femtosecond Laser on Electron--Phonon Relaxation Time 总被引:1,自引:0,他引:1
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The electron phonon relaxation time as functions of pulse width and fluence of femtosecond laser is studied based on the two-temperature model. The two-temperature model is solved using a finite difference method for copper target. The temperature distribution of the electron and the lattice along with space and time for a certain laser fluence is presented. The time-dependence of lattice and electron temperature of the surface for different pulse width and different laser fluence are also performed, respectively. Moreover, the variation of heat-affected zone per pulse with laser Auence is obtained. The satisfactory agreement between our numerical results and experimental data indicates that the electron-phonon relaxation time is reasonably accurate with the influences of pulse width and Auence of femtosecond laser. 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.
R.?L.?Vander?Wal 《Applied physics. B, Lasers and optics》2009,96(4):601-611
Successful implementation of laser-induced incandescence (LII) relies upon judicious choice of excitation and detection conditions.
Excitation conditions encompass choice of excitation wavelength and laser fluence. Detection conditions include choice of
detection wavelength, spectral band pass about the central wavelength, detection delay and duration relative to the excitation
laser pulse usually corresponding to the peak of the signal intensity. Examples of applying these parameters to LII are illustrated
by way of examples: soot/polycyclic aromatic hydrocarbon and metal aerosol systems. Tradeoffs must be recognized. Laser-induced
chemical and structural changes of the aerosol must be considered, particularly in light of heterogeneous aerosols. Diagnostics
of such changes are outlined as they will affect interpretation of the LII signal. Finally, calibration (for LII) must be
chosen to be appropriate for aerosols from practical sources as they may be mixed organic and inorganic composition.
A research paper in response to the call for papers from the Third International Discussion Meeting and Workshop on Laser-Induced
Incandescence July 30th–August 1st, Ottawa, Canada (2008). 相似文献
10.
11.
Dou K. Knobbe E.T. Parkhill R.L. Irwin B. Matthews L. Church K.H. 《Applied Physics A: Materials Science & Processing》2003,76(3):303-307
Surface structuring and compositioning in aluminum alloy 2024-T3 were demonstrated using a femtosecond pulse laser. Surface
nanostructuring was developed as a function of laser parameters and the surface micrographs of the scanning electron microscopy
were characterized as a function of incident laser fluence. Surface compositioning was performed by selectively removing the
elements on the surface of the sample. Femtosecond studies of highly excited electrons were performed by a pump–probe technique,
and the thermalization time was found to be in a range of 1.5–3 ps, increasing with incident fluence. The time-resolved measurement
is well matched to the numerical calculation.
Received: 6 September 2001 / Accepted: 18 July 2002 / Published online: 25 October 2002
RID="*"
ID="*"Corresponding author. Fax: +1-405/744-6811, E-mail: dou@okstate.edu 相似文献
12.
W. Holzer A. Penzkofer T. Pertsch N. Danz A. Bräuer E.B. Kley H. Tillmann C. Bader H.-H. Hörhold 《Applied physics. B, Lasers and optics》2002,74(4-5):333-342
Wave-guided thin-film distributed-feedback (DFB) polymer lasers are fabricated by spin coating a PPV-derived semiconducting
polymer, thianthrene-DOO-PPV, onto oxidised silicon wafers with corrugated second-order periodic gratings. The gratings are
written by reactive ion beam etching. Laser action is achieved by transverse pumping with picosecond laser pulses (wavelength
347.15 nm, duration 35 ps). The DFB-laser surface emission and edge emission are analysed. Outside the grating region the
polymer film is used for comparative wave-guided travelling wave laser (amplified spontaneous emission (ASE)) studies. The
pump pulse threshold energy density for wave-guided DFB-laser action (4–9 μJ cm-2) is found to be approximately a factor of two lower than the threshold for wave-guided travelling wave laser action. The
spectral width of the DFB laser (down to ΔλDFB≈0.07 nm) is considerably narrower than that of the travelling wave laser (ΔλTWL≈14 nm). The DFB-laser emission is highly linearly polarised transverse to the grating axis (TE mode). Only at high pump pulse
energy densities does an additional weak TM mode build up. The surface-emitted DFB-laser radiation has a low divergence along
the grating direction. For both the DFB lasers and the travelling wave lasers, gain saturation occurs at high excitation energy
densities.
Received: 7 January 2002 / Revised version: 15 February 2002 / Published online: 14 March 2002 相似文献
13.
S. Amoruso M. Armenante V. Berardi R. Bruzzese N. Spinelli 《Applied Physics A: Materials Science & Processing》1997,65(3):265-271
-2 ). The interpretation of the ion TOF distributions in terms of theoretical shifted Maxwell–Boltzmann distributions produces
a good agreement with the experimental data. This has allowed us to infer the ion flow velocity and temperature associated
with the measured TOF distributions, as well as the ion kinetic energies as a function of the laser fluence. We have also
studied the total ion yield at different laser fluences. Our results show that all the plume parameters investigated are increasing
functions of the laser fluence until a saturation plateau is reached at high fluences (>20 Jcm-2). We ascribe this saturation behav
iour to strong absorption and partial, or total, reflection of the laser light by the hot plasma produced by the leading edge
of the intense laser pulse. This interpretation is supported by a semi-quantitative analysis of the laser photon absorption
and ionization mechanisms in Al plasma, at both laser wavelengths.
Received: 6 January 1997/Accepted: 14 March 1997 相似文献
14.
Wai-Lun Chan Robert S. Averback D. G. Cahill 《Applied Physics A: Materials Science & Processing》2009,97(2):287-294
We use calorimetry to determine the energy absorption of femtosecond (fs) laser pulses as a function of incident fluence for
Ag, Ag alloys (Ag–Cu and Ag–Pt), and Pt. At low fluences, the measured absorption agrees well with reflectivity data derived
from ellipsometry measurements. For Ag and Ag–Cu, the absorbed energy increases nonlinearly with the incident fluence for
fluences larger than approximately half of the melting threshold. Near this threshold, the absorption increases by a factor
of 3–4. Similar nonlinear absorption is not observed in Pt or Ag–Pt. We propose that the nonlinear absorption is caused by
the excitation of d-band electrons below the Fermi surface. For pulse widths longer than 850 fs, the observed nonlinear absorption
in Ag diminishes, indicating that diffusive transport and not ballistic transport is the major mechanism of cooling at this
excitation level. 相似文献
15.
Ion synthesis and laser annealing of Cu nanoparticles in Al2O3 总被引:1,自引:0,他引:1
A.L. Stepanov V.N. Popok D.E. Hole I.B. Khaibullin 《Applied Physics A: Materials Science & Processing》2002,74(3):441-446
Al2O3 samples with Cu nanoparticles, synthesised by ion implantation at 40 keV with a dose of 1×1017 ion/cm2 and a current density from 2.5 to 12.5 μA/cm2, were annealed using ten pulses from a KrF excimer laser with a single pulse fluence of 0.3 J/cm2. The copper depth distribution, formation and modification of metal nanoparticles under the ion implantation and laser treatment
were studied by Rutherford backscattering (RBS), energy dispersive X-ray (EDX) analysis, atomic force microscopy (AFM) and
optical spectroscopy. It was found that laser annealing leads to a reduction in the nanoparticle size without diffusion of
metal atoms into the bulk. The change in particle size and the possibility for oxidation of the copper particles are examined
in the framework of Mie theory. Calculations presented show that under excimer laser treatment, Cu nanoparticles are more
likely to be reduced in size than to undergo oxidation.
Received: 19 April 2001 / Accepted: 7 November 2001 / Published online: 23 January 2002 相似文献
16.
A systematic theoretical study of laser-irradiated targets made of material with increasing atomic number has been performed.
The formation of energetic light ions resulting from the interaction of an intense ultrashort pulse laser with thin planar
targets is investigated theoretically with a two-dimensional relativistic electromagnetic particle-in-cell model. A common
parameter, the areal electron density of the foil, can be used to describe qualitatively targets made of different material.
By varying either the laser intensity or the target thickness we observe a gradual transition of various ion acceleration
mechanisms from one into another. Light ions, such as H+, Li3+, C6+, and Al13+, can be accelerated to GeV energies with existing laser systems at a laser fluence of 10–20 J/μm2. 相似文献
17.
D. R. Snelling K. A. Thomson F. Liu G. J. Smallwood 《Applied physics. B, Lasers and optics》2009,96(4):657-669
Laser-induced incandescence (LII) was used to derive temperatures of pulsed laser heated soot particles from their thermal
emission intensities detected at two wavelengths in a laminar ethylene/air co-annular diffusion flame. The results are compared
to those of a numerical nanoscale heat and mass transfer model. Both aggregate and primary particle soot size distributions
were measured using transmission electron microscopy (TEM). The model predictions were numerically averaged over these experimentally
derived size distributions. The excitation laser wavelength was 532 nm, and the LII signal was detected at 445 nm and 780 nm.
A wide range of laser fluence from very low to moderate (0.13 to 1.56 mJ/mm2) was used in the experiments. A large part of the temporal decay curve, beginning 12–15 nsec after the peak of the laser
excitation pulse, is successfully described by the model, resulting in the determination of accommodation coefficients, which
varies somewhat with soot temperature and is in the range of 0.36 to 0.46. However, in the soot evaporative regime, the model
greatly overpredicts the cooling rate shortly after the laser pulse. At lower fluences, where evaporation is negligible, the
initial experimental cooling rates, immediately following the laser pulse, are anomalously high. Potential physical processes
that could account for these effects are discussed. From the present data the soot absorption function, E(m), of 0.4 at 532 nm is obtained. A procedure for correcting the measured signals for the flame radiation is presented. It
is further shown that accounting for the local gas temperature increase due to heat transfer from soot particles to the gas
significantly improves the agreement in the temperature dependence of soot cooling rates between model and experiments over
a large range of laser fluences. 相似文献
18.
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
19.
为了提高脉冲激光制备薄膜的质量,准确掌握电声弛豫时间是关键,它对脉冲激光脉宽和能量密度的选取起着决定性的作用. 文中以铝靶材为例,利用经典的双温方程通过时域有限差分法(FDTD)得到电子、离子亚系统的温度随时间和位置演化的图像,进而得到电声弛豫时间的准确值. 这样便能准确划分热烧蚀和非平衡烧蚀,从而更好地控制激光的烧蚀过程. 同时找出了电声弛豫时间随激光脉宽以及能量密度变化的规律.
关键词:
飞秒激光
电声弛豫时间
双温方程
激光能量密度 相似文献
20.
J. M. Headrick F. Goulay P. E. Schrader H. A. Michelsen 《Applied physics. B, Lasers and optics》2011,104(2):439-450
We have measured time-resolved laser-induced incandescence of flame-generated soot under high-vacuum conditions (4.1×10−6 mbar) at an excitation wavelength of 532 nm with laser fluences spanning 0.06–0.5 J/cm2. We generated soot in an ethylene/air diffusion flame, introduced it into the vacuum system with an aerodynamic lens, heated
it using a pulsed laser with a spatially homogeneous and temporally smooth laser profile, and recorded LII temporal profiles
at 685 nm. At low laser fluences LII signal decay rates are slow, and LII signals persist beyond the residence time of the
soot particles in the detection region. At these fluences, the temporal maximum of the LII signal increases nearly linearly
with increasing laser fluence until reaching a plateau at ∼0.18 J/cm2. At higher fluences, the LII signal maximum is independent of laser fluence within experimental uncertainty. At these fluences,
the LII signal decays rapidly during the laser pulse. The fluence dependence of the vacuum LII signal is qualitatively similar
to that observed under similar laser conditions in an atmospheric flame but requires higher fluences (by ∼0.03 J/cm2) for initiation. These data demonstrate the feasibility of recording vacuum LII temporal profiles of flame-generated soot
under well-characterized conditions for model validation. 相似文献