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1.
Korte F. Serbin J. Koch J. Egbert A. Fallnich C. Ostendorf A. Chichkov B.N. 《Applied Physics A: Materials Science & Processing》2003,77(2):229-235
Detailed investigations of the possibilities for using femtosecond lasers for the nanostructuring of metal layers and transparent
materials are reported. The aim is to develop a simple laser-based technology for fabricating two- and three-dimensional nanostructures
with structure sizes on the order of several hundred nanometers. This is required for many applications in photonics, for
the fabrication of photonic crystals and microoptical devices, for data storage, displays, etc. Measurements of thermionic
electron emission from metal targets, which provide valuable information on the dynamics of femtosecond laser ablation, are
discussed. Sub-wavelength microstructuring of metals is performed and the minimum structure size that can be fabricated in
transparent materials is identified. Two-photon polymerization of hybrid polymers is demonstrated as a promising femtosecond
laser-based nanofabrication technology.
Received: 20 November 2002 / Accepted: 20 January 2003 / Published online: 28 May 2003
RID="*"
ID="*"Corresponding author. Fax: +49-511/2788-100, E-mail: ch@lzh.de 相似文献
2.
K. Venkatakrishnan B.K.A. Ngoi P. Stanley L.E.N. Lim B. Tan N.R. Sivakumar 《Applied Physics A: Materials Science & Processing》2002,75(4):493-496
Photomasks are the backbone of microfabrication industries. Currently they are fabricated by a lithographic process, which
is very expensive and time consuming since it is a multi-step process. These issues can be addressed by fabricating photomasks
by direct femtosecond laser writing, which is a single-step process and comparatively cheaper and faster than lithography.
In this paper we discuss our investigations on the effect of two types of laser writing techniques, namely front- and rear-side
laser writing, with regard to the feature size and the edge quality of a feature. It is proved conclusively that for the patterning
of masks, front-side laser writing is a better technique than rear-side laser writing with regard to smaller feature size
and better edge quality. Moreover the energy required for front-side laser writing is considerably lower than that for rear-side
laser writing.
Received: 22 May 2001 / Accepted: 14 September 2001 / Published online: 17 October 2001 相似文献
3.
The micromachining of hydroxyapatite (HAp) is highly important for orthopedics and dentistry, since human bone and teeth consist
mainly of HAp. We demonstrate ultrashort Ti:sapphire laser ablation of HAp, using pulse-widths of 50 fs, 500 fs, and 2 ps
at a wavelength of 820 nm and at 1 kpps. The crucial medical issue is to preserve the chemical properties of the machined
(ablated) surface. If the chemical properties of HAp change, the human bone or tooth cannot re-grow after laser processing.
Using X-ray photoelectron spectroscopy, we observe chemical properties of HAp ablated in air. The HAp is ablated at laser
fluences of 3.2 J/cm2 (6.4×1013 W/cm2 at 50 fs), 3.3 J/cm2 (6.6×1012 W/cm2 at 500 fs), and 9.6 J/cm2 (4.8×1012 W/cm2 at 2 ps), respectively. As a result it is found that the ablated surface is unchanged after laser ablation over the pulse-width
range used in this experiment.
Received: 7 October 2002 / Accepted: 20 January 2003 / Published online: 28 May 2003
RID="*"
ID="*"Corresponding author. Fax: +81-45/566-1533, E-mail: obara@obara.elec.keio.ac.jp 相似文献
4.
Arrays of conical-like spikes can be formed on silicon surface after irradiated with femtosecond laser pulses in ambient of SF6 or N2. In this article, we report our observations on how the shape of the spikes formed on silicon surface varies with the polarization of laser beam. The experimental results show that, with circular polarized laser irradiation, the shape of the spikes is conical; however, with linearly polarized laser irradiation, the spikes show elliptic conical shape, and the long-axes are perpendicular to the direction of the polarization of laser beam. The asymmetric shape of spikes produced by linearly polarized laser beam can be explained by considering the polarization dependence of Fresnel-refraction. 相似文献
5.
M. Hentschel S. Uemura Z. Cheng S. Sartania G. Tempea C. Spielmann F. Krausz 《Applied physics. B, Lasers and optics》1999,68(1):145-148
Received: 9 June 1998/Revised version: 4 November 1998 相似文献
6.
A.A. Babin D.V. Kartashov A.M. Kiselev V.V. Lozhkarev A.N. Stepanov A.M. Sergeev 《Applied physics. B, Lasers and optics》2002,75(4-5):509-514
. We report on the experimental and theoretical study of spectrum transformation and frequency blue-shift of femtosecond laser
pulses with intensities up to 2×1016 W/cm2, propagating in glass capillary tubes under gas ionization. Monomode optical guiding with 45% transmission efficiency is
demonstrated in a 100-μm-diameter, 20-cm length capillary. A broadening of the initial spectrum as much as several initial
spectrum widths is achieved. Besides the broadening, the mean frequency of the output radiation in the spectrum experiences
a blue-shift of up to several initial spectrum widths, caused by the non-stationary, non-linear process of gas ionization.
Our numerical simulations, in the form of a simple one-dimensional model for the propagation of intense laser pulses in gas-filled
capillaries, are in good qualitative agreement with the experimental results. These simulations show the possibility of significant
compression of an output pulse in a simple compression scheme (e.g. a piece of silica glass with normal dispersion), which
is very important for obtaining laser pulses with few optical cycles at the millijoule energy level.
Received: 25 September 2001 / Revised version: 6 December 2001 / Published online: 25 September 2002
RID="*"
ID="*"Corresponding author. Fax: +7-8312/363-792, E-mail: dekart@ufp.appl.sci-nnov.ru 相似文献
7.
S. Tzortzakis G. Méchain G. Patalano M. Franco B. Prade A. Mysyrowicz 《Applied physics. B, Lasers and optics》2003,76(5):609-612
We report the first observation of the attachment of two single plasma filaments created collinearly in the atmosphere by
IR femtosecond laser pulses. The linked filamentary structure is electrically conductive and emits sub-THz radiation over
its entire length. Concatenation is achieved only for a specific time ordering between the two initial laser pulses. The pulse
producing the filament closer to the laser source must be retarded with respect to the other pulse. This special time ordering
is attributed to the acceleration of light in a self-guided pulse.
Received: 4 March 2003 / Published online: 14 May 2003
RID="*"
ID="*"Corresponding author. Fax: +33-1/6931-9996, E-mail: stzortz@ensta.fr 相似文献
8.
Received: 17 December 1998 相似文献
9.
N. Bärsch K. Körber A. Ostendorf K.H. Tönshoff 《Applied Physics A: Materials Science & Processing》2003,77(2):237-242
Although lasers are generally able to machine silicon, the major material in many microsystems applications, doing so without
influencing the physical properties of the bulk material remains an important challenge. Ultrafast lasers, in particular,
with their potential to precisely ablate all kinds of solid materials, are able to perform such processes with high efficiency
and accuracy. This article starts with an overview of the general interaction of ultrafast laser radiation with semiconductors,
explaining the absorption processes and different fluence regimes for the ablation of silicon. Major parameter influences,
especially for cutting processes in thin silicon, are described. By varying pulse energies, beam shaping methods, the beam
polarization, and temperatures, the cutting quality and speed can be significantly influenced. One important quality aspect,
besides kerf widths and surface roughness, is the amount of back-side chipping when cutting brittle materials. Achievements
in speed enhancement using linear focus shapes are presented, with cutting speeds up to five times higher than by conventional
spot-focusing. On the other hand, laser processes that cut with a spot focus offer the possibility of free-shape cutting,
which is explained using the example of wafers carrying silicon chips with highly increased package densities.
Received: 10 December 2002 / Accepted: 20 January 2003 / Published online: 28 May 2003
RID="*"
ID="*"Corresponding author. Fax: +49-511/2788-100, E-mail: nb@lzh.de 相似文献
10.
Remote sensing of the atmosphere using ultrashort laser pulses 总被引:2,自引:0,他引:2
P. Rairoux H. Schillinger S. Niedermeier M. Rodriguez F. Ronneberger R. Sauerbrey B. Stein D. Waite C. Wedekind H. Wille L. Wöste C. Ziener 《Applied physics. B, Lasers and optics》2000,71(4):573-580
Theoretical and experimental studies were performed on the propagation of ultrashort optical terawatt pulses through the atmosphere.
Propagation simulations of intense sub-picosecond pulses show that non-linear processes, such as white light generation, can
be initiated at a chosen distance by selecting an appropriate group velocity dispersion. With this technique, a white light
continuum was generated in the atmosphere whose spectral distribution was characterised in the visible and near infra-red.
Applications of this novel light source for atmospheric remote sensing were investigated, combining lidar and time-resolved
broadband absorption spectroscopy techniques. Measurements were performed on the oxygen molecule and water vapour. A comparison
between the experimental results and the tabulated spectroscopic data led to an excellent correlation with measurements made
on water vapour whereas observations on the oxygen showed discrepancy. This study demonstrates that the remote generation
of a white light source represents a new way to access the range-resolved multi-trace gas analysis in the atmosphere.
Received: 8 December 1999 / Revised version: 18 May 2000 / Published online: 16 August 2000 相似文献
11.
A commercial femtosecond pulse laser was used to study the interaction of ultrashort laser pulses with aluminum. Tests were conducted to measure the average drilling rate over a range of laser pulse energies in both air and vacuum at the wavelengths corresponding to the fundamental and second harmonic of the laser. For the fundamental wavelength, it was observed that the drilling rates in vacuum were significantly higher than that for drilling in atmospheric air. For the laser beam that was converted to second harmonic, the drilling rate in vacuum at the same energy was slightly lower than that for drilling in air. The observed results can be explained by the presence of an energetic nanosecond pedestal in the laser pulse produced by the femtosecond laser system. This nanosecond component provides a major contribution into drilling and it is strongly affected by the optical breakdown plasma that reduces the drilling rate in air. Conversion to second harmonic reduces the relative energy content of the nanosecond component resulting in a higher contrast femtosecond pulse that is not affected by the near surface plasma. The presence of air results in self-focusing of the second harmonic laser beam, causing an increased drilling rate as compared to the interaction in vacuum. 相似文献
12.
Intensity clamping and re-focusing of intense femtosecond laser pulses in nitrogen molecular gas 总被引:3,自引:0,他引:3
A. Becker N. Aközbek K. Vijayalakshmi E. Oral C.M. Bowden S.L. Chin 《Applied physics. B, Lasers and optics》2001,73(3):287-290
We present results of measurements of fluorescence spectra due to the interaction of a Ti:sapphire laser pulse with N2 molecules at different gas pressures and pulse energies. The analysis of the data together with the results of numerical
simulations, using a propagation model, reveal signatures of the phenomena of intensity clamping and of re-focusing of the
laser pulse at high gas pressure. The laser pulse energy for intensity clamping as a function of the gas pressure is determined.
Received: 21 May 2001 / Revised version: 10 July 2001 / Published online: 19 September 2001 相似文献
13.
Laser ablation of titanium in vacuum was performed using single- and dual-pulse regime in order to study crater formation. Crater profiles were analyzed by optical microscopy. It was found that the repetition-rate plays an important role in a process of laser ablation. The drilling is most effective for the highest repetition-rate. For the same total number of laser pulses clear drilling enhancement was achieved by dual-pulse regime of ablation in comparison to single-pulse regime. The strongest ablation rate in dual-pulse regime was achieved for the delay time between the pulses τ = 370 ns. Results are discussed in terms of decreased ablation threshold due to continuous heating of the target during the experiment. 相似文献
14.
We demonstrate an optical limiter for ultra-short (∼100-fs) laser pulses. The device has a dynamic range (= damage energy/onset-of-limiting
energy) of more than 10000 and an onset-of-limiting energy of only ∼10 nJ. The output-pulse energy is kept below 1.3 μJ. The
limiting mechanism is based on two-photon absorption and refractive nonlinearities in a 20-mm piece of ZnSe. We discuss the
importance of the different nonlinearities, damage issues, and guidelines for the construction of the device.
Received: 20 December 2001 / Revised version: 25 March 2002 / Published online: 8 May 2002 相似文献
15.
Characterisation of the plasma plume induced by femtosecond laser-metal interactions has been carried out using a Langmuir probe. A double peak distribution of ablated ions and electrons has been recorded during time of flight (TOF) experiments for three metals studied (Ag, Cu and Ni). The first peak which occurs earliest in time is attributed to a surface layer of contaminants on the metal surface as it is shown to disappear after several laser shots. The re-growth of this peak, thought to be due to a recontamination process on the surface of the metal, is the subject of this paper. Two re-contamination mechanisms were considered; adsorption of contaminants from the ambient gas, and surface diffusion effects from the surrounding contaminants. Re-contamination rates for Ag, Cu and Ni were studied under two distinct gas pressures to investigate the contamination effects from the ambient. Effects arising from surface diffusion were investigated by raising the temperature of the metal sample to increase the surface mobility of the contaminants. The total contribution of contamination species present in the ablation plume was estimated by conducting angular distribution measurements of the plume. Surface diffusion of the surrounding contaminants was found to be the dominant recontamination process. 相似文献
16.
Yanhua Han 《Applied Surface Science》2009,255(17):7524-7528
Two-dimensional ‘hat-scratch’ structures are fabricated on silica glass by the interference of three non-coplanar beams originating from a single femtosecond laser pulse. The scanning electron microscope (SEM) characterizations show that the as-formed structures are composed of hat holes and scratch marks. The experimental results indicate that the structures are dependent on the intensity of laser beam. The formation of the two-dimensional ‘hat-scratch’ structures is mainly due to the combined laser ablation effects including ionization, shock wave, plasma expansion, and phase explosion. 相似文献
17.
David J. Hwang Kuniaki Hiromatsu Hirofumi Hidai Costas P. Grigoropoulos 《Applied Physics A: Materials Science & Processing》2009,94(3):555-558
Straight through-holes of high aspect ratio have been fabricated in glass by femtosecond laser pulses, utilizing unique characteristics
of ultrafast lasers such as volumetric multi-photon absorption and nonlinear self-focusing. In this study, interestingly,
the drilling process was initiated and progressed in a self-regulated manner, while the laser focus was fixed through the
specimen at the neighborhood of the rear surface that was in contact with liquid during the entire drilling process. The deposition
of laser energy along the nonlinearly extended focal range and the guided drilling along the pre-defined region are explained
based on time-resolved optical transmission and emission measurements. 相似文献
18.
Modulation grating has been achieved by two interfered femtosecond laser pulses on the surface of the silica glass. The modulation grating formed at the middle of each bulge of the common grating and was attributed to the higher-order modulation arising from second-harmonic generation (SHG) of the femtosecond laser pulse incident to the surface of silica glass. The periods and depths of the fundamental grating and the modulation grating have been observed by using an atomic force microscopy (AFM). Experimental results show that the average depth of the modulation grating is nearly a half of the depth of the fundamental grating. 相似文献
19.
Visible femtosecond (fs) laser pulses have been obtained in a dye solution with a very simple traveling wave collinear configuration.
A femtosecond Ti:sapphire laser (790 nm) pumps the dye solution by two-photon absorption and simultaneously generates supercontinuum,
which seeds a light-amplification mechanism. Cross-correlation frequency-resolved optical gating measurements reveal a chirped
structure in the dye pulse. The shortest pulse duration achieved is 170 fs and the overall energy efficiency of the process
is typically 25%.
Received: 22 March 2001 / Revised version: 4 July 2001 / Published online: 19 September 2001 相似文献
20.
E.G. Gamaly A.V. Rode A. Perrone A. Zocco 《Applied Physics A: Materials Science & Processing》2001,73(2):143-149
We present two sets of experimental results on the ablation-rate decrease with increase of the number of consecutive laser
pulses hitting the same spot on the target surface. We have studied laser ablation of a carbon target with nanosecond pulses
in two different interaction regimes: one with a XeCl laser (λ=308 nm) and the other with a Nd:YAG laser (λ=1064 nm), in both
cases at the intensity ∼5×108 W/cm2 Two different mechanisms were found to be responsible for the ablation-rate decrease; they are directly related to the two
different laser–matter interaction regimes. The UV-laser interaction is in the regime of transparent vapour (surface absorption).
The increase of the neutral vapour density in the crater produced by the preceding laser pulses is the main reason for the
decrease of ablation rate. With the IR laser each single laser pulse interacts with a partially ionised plume. With increase
of the number of pulses hitting the same spot on the target surface, the laser–matter interaction regime gradually changes
from the near-surface absorption to the volume absorption, resulting in the decrease in absorption in the target and thus
in the decrease in the ablation rate. The change in the evaporation rate was considered for both vacuum and reactive-gas environments.
Received: 21 February 2001 / Accepted: 26 February 2001 / Published online: 23 May 2001 相似文献