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1.
The ablation behavior of single crystalline sapphire with nanosecond laser pulses at 157 nm wavelength is investigated. Ablation
rates of about 10 to 100 nm/pulse are obtained at fluences ranging from 1 to 9 J/cm2. At moderate fluences, incubation behavior is observed, i.e. ablation starts after material modification by a number of laser
pulses. The ablation can be utilized to fabricate sapphire micro-optics. The capability of creating lenses or gratings on
the tip of sapphire fibers is demonstrated. Multilevel diffractive optical elements and high resolution gratings with 1 μm
period are fabricated on planar sapphire substrates. 相似文献
2.
A. Bartnik H. Fiedorowicz R. Jarocki J. Kostecki A. Szczurek M. Szczurek 《Applied physics. B, Lasers and optics》2009,96(4):727-730
Surface modification and micro-structuring of polymers for different application is mainly performed using ultraviolet (UV)
radiation from excimer lamps or excimer lasers. In this case, however, the radiation penetration depth may exceed 100 μm,
thereby degrading the polymer deep inside. On the other hand, extreme ultraviolet (EUV) radiation is absorbed in a layer approximately
100 nm thick only. In this work, the radiation from a laser-plasma EUV source based on a double-stream gas-puff target is
focused with a gold-coated ellipsoidal collector for surface modification of polymethylmethacrylate (PMMA). The spectrum of
the focused radiation consists of a narrow feature with maximum at 10 nm and a long-wavelength tail up to 70 nm. The PMMA
samples are mounted in the focal plane of the EUV collector or at some distance downstream this plane and irradiated for 10–60
s with 10-Hz repetition rate. The irradiated polymer samples were investigated using a scanning electron microscope. When
the EUV fluence exceeds 10 mJ/cm2, smooth ablation of PMMA was obtained. For lower fluences but close to this value, strong surface modifications appeared. 相似文献
3.
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
4.
Sonja Hermann Nils-Peter Harder Rolf Brendel Dirk Herzog Heinz Haferkamp 《Applied Physics A: Materials Science & Processing》2010,99(1):151-158
In this work, we report on laser ablation of thermally grown SiO2 layers from silicon wafer substrates, employing an 8–9 ps laser, at 1064 (IR), 532 (VIS) and 355 nm (UV) wavelengths. High-intensity
short-pulse laser radiation allows direct absorption in materials with bandgaps higher than the photon energy. However, our
experiments show that in the intensity range of our laser pulses (peak intensities of <2×1012 W/cm2) the removal of the SiO2 layer from silicon wafers does not occur by direct absorption in the SiO2 layer. Instead, we find that the layer is removed by a “lift off” mechanism, actuated by the melting and vaporisation of
the absorbing silicon substrate. Furthermore, we find that exceeding the Si melting threshold is not sufficient to remove
the SiO2 layer. A second threshold exists for breaking of the layer caused by sufficient vapour pressure. For SiO2 layer ablation, we determine layer thickness dependent minimum fluences of 0.7–1.2 J/cm2 for IR, 0.1–0.35 J/cm2 for VIS and 0.2–0.4 J/cm2 for UV wavelength. After correcting the fluences by the reflected laser power, we show that, in contrast to the melting threshold,
the threshold for breaking the layer depends on the SiO2 thickness. 相似文献
5.
Ablation of polyetheretherketone (PEEK), a high temperature thermoplastic, by XeCl laser radiation occurs at fluences in excess of 0.07±0.01 J cm–2. The volatile products of ablation are CO and C2H2 with smaller quantities of CH4, C4H2, C6H6 and other C3 and C4 hydrocarbons. At fluences close to the threshold ablation produces involatile material of relatively high molecular weight but at high fluences extensive disruption of the PEEK structure occurs with conversion of all of the oxygen in the polymer to carbon monoxide. 相似文献
6.
We have investigated the all-optical generation of ions by photo-ionisation of atoms generated by pulsed laser ablation. A
direct comparison between a resistively heated oven source and pulsed laser ablation is reported. Pulsed laser ablation with
10 ns Nd:YAG laser pulses is shown to produce large calcium flux, corresponding to atomic beams produced with oven temperatures
greater than 650 K. For an equivalent atomic flux, pulsed laser ablation is shown to produce a thermal load more than one
order of magnitude smaller than the oven source. The atomic beam distributions obey Maxwell–Boltzmann statistics with most
probable speeds corresponding to temperatures greater than 2200 K. Below a threshold pulse fluence between 280 mJ/cm2 and 330 mJ/cm2, the atomic beam is composed exclusively of ground-state atoms. For higher fluences ions and excited atoms are generated. 相似文献
7.
D. R. Leal-Ayala J. M. Allwood T. A. M. Counsell 《Applied Physics A: Materials Science & Processing》2011,105(4):801-818
In this article, lasers in the ultraviolet, visible and infrared light spectra working with pulse widths in the nanosecond
range are applied to a range of toner-paper combinations to determine their ability to remove toner. If the laser energy fluence
can be chosen to stay below the ablation threshold of paper at the same time that it surpasses that of toner, paper could
be cleaned and re-used instead of being recycled or disposed into a landfill. This could significantly reduce the environmental
impact of paper production and use. Although there are a variety of paper conservation studies which have investigated the
effects of laser radiation on blank and soiled paper, none has previously explored toner-print removal from paper by laser
ablation. Colour analysis under the L
∗
a
∗
b
∗ colour space and SEM examination of the outcome indicate that it is possible to remove toner from paper without damaging
and discolouring the substrate. Best results are obtained when employing visible radiation at a wavelength of 532 nm working
with a pulse width of 4 ns and energy fluences under 1.6 J/cm2. This means that it is technically feasible to remove toner-print for paper re-use. 相似文献
8.
Ultrashort-pulse laser ablation of indium phosphide in air 总被引:4,自引:0,他引:4
J. Bonse J.M. Wrobel J. Krüger W. Kautek 《Applied Physics A: Materials Science & Processing》2001,72(1):89-94
Ablation of indium phosphide wafers in air was performed with low repetition rate ultrashort laser pulses (130 fs, 10 Hz)
of 800 nm wavelength. The relationships between the dimensions of the craters and the ablation parameters were analyzed. The
ablation threshold fluence depends on the number of pulses applied to the same spot. The single-pulse ablation threshold value
was estimated to be φth(1)=0.16 J/cm2. The dependence of the threshold fluence on the number of laser pulses indicates an incubation effect. Morphological and
chemical changes of the ablated regions were characterized by means of scanning electron microscopy and Auger electron spectroscopy.
Received: 30 May 2000 / Accepted: 31 May 2000 / Published online: 23 August 2000 相似文献
9.
In the present paper, polyimide surfaces were processed with pulsed KrF laser radiation at fluences near the ablation threshold.
The morphology of the processed surfaces was studied by scanning electron microscopy and chemical analyses performed by electron
dispersive spectroscopy. The formation of conical structures was observed for radiation fluences lower than 0.5 J/cm2. The areal density of cones increases with the number of pulses and decreases with the radiation fluence. At low fluences
(<150 J/cm2), cones are formed due to shadowing by calcium phosphate impurities while for higher fluences the main mechanism of cones
formation is believed to be radiation hardening. 相似文献
10.
Ablation of bulk metals (Al, Cu) has been investigated in situ by means of high-resolution pump-probe photography using pump
laser radiation of pulse duration t
p=80 fs, at wavelength of 820 nm.
Depending on material-specific parameters, qualitatively different ablation phenomena have been observed. Structural analysis
by electron and optical microscopies reveals rosette-like surface structures showing the morphology of the ablated regions.
The temporal development of the ablation dynamics can be conditionally categorized into different characteristic time regions.
Particularly, laser induced melt injection has been observed in the time range of 700 ns to 1.1 μs after the initial laser-metal
interaction. 相似文献
11.
D. Puerto W. Gawelda J. Siegel J. Bonse G. Bachelier J. Solis 《Applied Physics A: Materials Science & Processing》2008,92(4):803-808
We have studied the plasma formation and ablation dynamics in fused silica upon irradiation with a single 120 fs laser pulse
at 800 nm by using fs-resolved pump-probe microscope. It allows recording images of the laser-excited surface at different
time delays after the arrival of the pump pulse. This way, we can extract both the temporal evolution of the surface reflectivity
and transmission, at 400 nm, for different spatial positions in the spots (and thus for different local fluences) from single
series of images. At fluences well above the visible ablation threshold, a fast and large increase of the reflectivity is
induced by the formation of a dense free-electron plasma. The maximum reflectivity value is reached within ≈1.5 ps, while
the normalized transmission decreases within ≈400 fs. The subsequent temporal evolution of both transient reflectivity and
transmission are consistent with the occurrence of surface ablation. In addition, the time-resolved images reveal the existence
of a free-electron plasma distribution surrounding the visible ablation crater and thus formed at local fluences below the
ablation threshold. The lifetime of this sub-ablation plasma is ≈50 ps, and its maximum electron density amounts to 5.5×1022 cm−3. 相似文献
12.
A. Costela J. M. Figuera F. Florido I. García-Moreno E. P. Collar R. Sastre 《Applied Physics A: Materials Science & Processing》1995,60(3):261-270
Data on the ablation of Poly(Methyl MetAcylate) (PMMA) and Poly(2-Hydroxyethyl MetAcylate) (PHEMA) with 0%, 1% and 20% of Ethylene Glycol DiMethAcrylate (EGDMA) as crosslinking monomer by 193, 222 and 308 nm laser radiation are presented. Direct photoetching of PMMA at 308 nm is demonstrated for laser fluences ranging from 2 to 18 J/cm2. The ablation rate of PHEMA is lower than the corresponding to PMMA and decreases when the amount of EGDMA increases. The determination of the absorbed energy density required to initiate significant ablation suggests that the photoetching mechanism is similar for all the polymers studied and is a function of the irradiation wavelength. The Beer-Lambert law, the Srinivasan, Smrtic and Babu (SSB) theory and the kinetic model of the moving interface are used to analyze the experimental results. It is shown that only the moving interface theory fits well the etch rate for all the selected polymers at the three radiation wavelengths. 相似文献
13.
T. Lippert M. Hauer C.R. Phipps A. Wokaun 《Applied Physics A: Materials Science & Processing》2003,77(2):259-264
The ablation characteristics of various polymers were studied at low and high fluences for an irradiation wavelength of 308 nm.
The polymers can be divided into three groups, i.e. polymers containing triazene groups, designed ester groups, and reference
polymers, such as polyimide. The polymers containing the photochemically most active group (triazene) exhibit the lowest thresholds
of ablation (as low as 25 mJ cm-2) and the highest etch rates (e.g. 250 nm/pulse at 100 mJ cm-2), followed by the designed polyesters and then polyimide. Neither the linear nor the effective absorption coefficients have
a clear influence on the ablation characteristics. The different behavior of polyimide might be explained by a pronounced
thermal part in the ablation mechanism. The laser-induced decomposition of the designed polymers was studied by nanosecond
interferometry and shadowgraphy. The etching of the triazene polymer starts and ends with the laser pulse, indicating photochemical
ablation. Shadowgraphy reveals mainly gaseous products and a pronounced shockwave in air. The designed polymers were tested
for an application as the polymer fuel in laser plasma thrusters.
Received: 21 October 2002 / Accepted: 20 January 2003 / Published online: 28 May 2003
RID="*"
ID="*"Corresponding author. Fax: +41-56/3104-412, E-mail: thomas.lippert@psi.ch 相似文献
14.
J. Heitz J.D. Pedarnig D. Bäuerle G. Petzow 《Applied Physics A: Materials Science & Processing》1997,65(3):259-261
3 N4 has been investigated. The ablation threshold in air, Φth, is around 0.3±0.1 J/cm2 with ArF- and 0.9±0.2 J/cm2 with KrF-laser radiation. With fluences Φth<Φ<4 J/cm2 the irradiated surface is either very flat or it exhibits a cone-type structure, depending on the number of laser pulses
employed. With fluences of 5 to 10 J/cm2, the sample surface becomes very smooth, much smoother than the original mechanically polished surface. Pores, scratches,
and cracks observed on the non-irradiated surface are absent within the illuminated area. In this regime, the ablation rates
are typically 0.1 to 0.2 μm/pulse.
Received: 10 April 1997/Accepted: 11 April 1997 相似文献
15.
Robert Lloyd Amin Abdolvand Marc Schmidt Philip Crouse David Whitehead Zhu Liu Lin Li 《Applied Physics A: Materials Science & Processing》2008,93(1):117-122
Utilising a Nd:YVO4 laser (wavelength of 532 nm, pulse duration of 8 ns, repetition rate of 30 kHz) and a Nd:YAG laser (wavelength of 1064 nm,
pulse duration of 7 ns, repetition rate of 25 kHz), it was found that during the pulsed laser ablation of metal targets, such
as stainless steel, periodic nodular microstructures (microcones) with average periods ranging from ∼30 to ∼50 μm were formed.
This period depends on the number of accumulated laser pulses and is independent of the laser wavelength. It was found that
the formation of microcones could occur after as little as 1500 pulses/spot (a lower number than previously reported) are
fired onto a target surface location at laser fluence of ∼12 J/cm2, intensity of ∼1.5 GW/cm2. The initial feedback mechanism required for the formation of structures is attributed to the hydrodynamic instabilities
of the melt. In addition to this, it has been shown that the structures grow along the optical axis of the incoming laser
radiation. We demonstrate that highly regular structures can be produced at various angles, something not satisfactorily presented
on metallic surfaces previously. The affecting factors such as incident angle of the laser beam and the structures that can
be formed when varying the manner in which the laser beam is scanned over the target surface have also been investigated. 相似文献
16.
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
17.
M. Jahn J. Richter R. Weichenhain-Schriever J. Meinertz J. Ihlemann 《Applied Physics A: Materials Science & Processing》2010,101(3):533-538
We investigate the ablation of SiO
x
thin films on fused silica substrates using single-pulse exposures at 193 nm and 248 nm. Two ablation modes are considered:
front side (the surface of a film is irradiated from above) and rear side (a film is irradiated through its supporting substrate).
Fluence is varied from below 200 mJ/cm2 to above 3 J/cm2. SiO
x
films of thickness 200 nm, 400 nm, and 600 nm are ablated. In the case of rear-side illumination, at moderate fluences (around
0.5 mJ/cm2) the ablation depth corresponds roughly to the film thickness, above 1 J/cm2 part of the substrate is ablated as well. In the case of front-side ablation the single-pulse ablation depth is limited for
all film thicknesses to less than 200 nm even at fluences up to 4 J/cm2. Experimental results are discussed in relation to film thickness, fluence, and ablation mode. Simple numerical calculations
are performed to clarify the influence of heat transport on the ablation process. 相似文献
18.
B. Hopp G. Kecskeméti T. Smausz T. Ajtai A. Filep N. Utry A. Kohut Z. Bozóki G. Szabó 《Applied Physics A: Materials Science & Processing》2012,107(2):429-435
Preparation of organic thin layers on various special substrates using the pulsed laser deposition (PLD) technique is an important
task from the point of view of bioengineering and biosensor technologies. Earlier studies demonstrated that particle ejection
starts during the ablating laser pulse resulting in significant shielding effects which can influence the real fluence on
the target surface and consequently the efficiency of layer preparation. In this study, we introduce a photoacoustic absorption
measurement technique for in-situ characterization of ablated particles during PLD experiments. A KrF excimer laser beam (λ=248 nm, FWHM=18 ns) was focused onto pepsin targets in a PLD chamber; the applied laser fluences were 440 and 660 mJ/cm2. We determined the wavelength dependence of optical absorption and mass specific absorption coefficient of laser ablation
generated pepsin aerosols in the UV–VIS–NIR range. On the basis of our measurements, we calculated the absorbance at the ablating
laser wavelength, too. We demonstrated that when the laser ablation generated pepsin aerosols spread through the whole PLD
chamber the effect of absorptivity is negligible for the subsequent pulses. However, the interaction of the laser pulse and
the just formed particle cloud generated by the same pulse is more significant. 相似文献
19.
S. Lazare A. Sionkowska M. Zaborowicz A. Planecka J. Lopez M. Dijoux C. Louména M.-C. Hernandez 《Applied Physics A: Materials Science & Processing》2012,106(1):67-77
Laser microprocessing of several biopolymers from renewable resources is studied. Three proteinic materials were either extracted
from the extracellular matrix like Silk Fibroin/Sericin and collagen, or coming from a commercial source like gelatin. All
can find future applications in biomedical experimentation, in particular for cell scaffolding. Films of ∼hundred of microns
thick were made by aqueous solution drying and laser irradiation. Attention is paid to the properties making them processable
with two laser sources: the ultraviolet and nanosecond (ns) KrF (248 nm) excimer and the infrared and femtosecond (fs) Yb:KGW
laser. The UV radiation is absorbed in a one-photon resonant process to yield ablation and the surface foaming characteristics
of a laser-induced pressure wave. To the contrary, resonant absorption of the IR photons of the fs laser is not possible and
does not take place. However, the high field of the intense I>∼1012 W/cm2 femtosecond laser pulse ionizes the film by the multiphoton absorption followed by the electron impact mechanism, yielding
a dense plasma capable to further absorb the incident radiation of the end of the pulse. The theoretical model of this absorption
is described in detail, and used to discuss the presented experimental effects (cutting, ablation and foaming) of the fs laser.
The ultraviolet laser was used to perform simultaneous multiple spots experiments in which energetic foaming yields melt ejection
and filament spinning. Airborne nanosize filaments “horizontally suspended by both ends” (0.25 μm diameter and 10 μm length)
of silk biopolymer were observed upon irradiation with large fluences. 相似文献
20.
I. Gallardo K. Hoffmann J. W. Keto 《Applied Physics A: Materials Science & Processing》2009,94(1):65-72
Laser Ablation of Microparticles (LAM) is a process of nanoparticle formation in which microparticles in a flowing aerosol
are continuously ablated by high-power laser pulses. For the first time, we have produced CdSe/ZnS core/shell nanoparticles
using a double ablation apparatus, designed to undergo a two-step LAM process. This process can be inverted to produce ZnS/CdSe
core/shell nanoparticles. The present work focuses on the range around ∼15 nm radius heterostructures and uses high-resolution
transmission electron microscopy (HRTEM) to image core and shells. For smaller particles, core shell structures have been
detected with energy dispersive spectroscopy (EDS) 5 nm spot size beam and fast Fourier transform (FFT) spectra. Differences
in the ablation behavior were measured between the two IIB–VIA type semiconductors. 相似文献