共查询到20条相似文献,搜索用时 31 毫秒
1.
N. G. Semaltianos S. Logothetidis W. Perrie S. Romani R. J. Potter S. P. Edwardson P. French M. Sharp G. Dearden K. G. Watkins 《Journal of nanoparticle research》2010,12(2):573-580
Silicon nanoparticles were generated by femtosecond laser [387 nm, 180 fs, 1 kHz, pulse energy = 3.5 μJ (fluence = 0.8 J/cm2)] ablation of silicon in deionized water. Nanoparticles with diameters from ~5 up to ~200 nm were observed to be formed in
the colloidal solution. Their size distribution follows log-normal function with statistical median diameter of ≈20 nm. Longer
ablation time leads to a narrowing of the nanoparticle size distribution due to the interaction of the ablating laser beam
with the produced nanoparticles. Raman spectroscopy measurements confirm that the nanoparticles exhibit phonon quantum confinement
effects and indicate that under the present conditions of ablation they are partially amorphous. 相似文献
2.
J. J. J. Kaakkunen K. Paivasaari M. Kuittinen T. Jaaskelainen 《Applied Physics A: Materials Science & Processing》2009,94(2):215-220
Recently, the enhancing of bulk metals optical absorption with focused femtosecond pulses was demonstrated. This absorption
enhancement is caused by different nano- and micro-structures which are formed during laser ablation with ultrashort pulses.
In this paper we study the evolution of the surface structures using interferometric ablation and compare it to normal fs-ablation.
Previously we have shown that interferometric femtosecond ablation is an efficient method to fabricate absorbing metal surfaces.
In this study we ablated large areas of hole-array structures with different pulse numbers in polished stainless steel and
copper samples. The evolution of surface morphology and the depth of the holes for these structured surfaces are presented.
In addition, the reflectance of laser generated surface structures are measured at the wavelength range of 200–2300 nm using
a standard spectrophotometer. 相似文献
3.
A. F. M. Y. Haider S. Sengupta K. M. Abedin Aminul I. Talukder 《Applied Physics A: Materials Science & Processing》2011,105(2):487-495
A colloidal solution of gold nanoparticles in deionized nanopure water was produced by laser ablation technique without the
use of any chemical/surfactant. Spectral characterization and morphological studies of these nanoparticles were carried out
by UV-Vis Spectroscopy and Scanning Electron Microscopy, respectively. A number of variables of the ablating laser pulse have
been used to control the size of the fabricated nanoparticles. Excellent correlation between ablating laser pulse parameter
and optical and morphological parameters of the gold colloids were obtained. The peak of the extinction spectra shows a monotonic
blue shift for laser fluence of 410 J/cm2 and above. Below this the extinction peak remains fairly constant in wavelength. Blue shifts of the extinction spectra were
also observed with increasing re-ablation time of previously ablated gold colloids. Possible explanations of all these observations
are discussed. 相似文献
4.
Using DCM dye grains and light of different wavelengths generated by two CW laser diodes that oscillate in the near-infrared
wavelength region, visible light emission from dye grains due to near-infrared excitation based on a nonadiabatic, nondegenerate
excitation process was observed for the first time. Unlike sum-frequency generation with nonlinear polarization, the difference
in polarization angles of the two beams did not affect the emitted light intensity. Optical sampling based on this nonadiabatic,
nondegenerate excitation principle was demonstrated for the first time. The optical pulse shape in the wavelength band of
λ=1250–1350 nm, which is close to the wavelength range used for optical fiber communications, was measured with a temporal
resolution of 0.8–1.1 ps. 相似文献
5.
N. Jegenyes J. Etchepare B. Reynier D. Scuderi A. Dos-Santos Z. Tóth 《Applied Physics A: Materials Science & Processing》2008,91(3):385-392
The evolution of a fs laser generated plume on copper was studied by dual laser pulses. The plume generated by the first pulse
(620 nm) was excited by the second, delayed pulse (310 nm). The actual state of the plume was monitored by detecting the intensities
of the emitted light and the reflected delayed pulse from the interaction range, i.e. 0–150 μm above the surface. Four peaks
were observed in the 0–1400 ps time range and assigned to appearance of electrons, ions, atomic species and nanoparticles.
Accordingly, the timing of the creation and ejection of these species was determined. By integrating the intensity of the
nanoparticle peak, the production yield of the nanoparticles and its dependence on the ablating laser fluence was calculated.
The ablation products were deposited on a Si substrate, too, and analyzed by atomic force microscopy and scanning electron
microscopy. The results of the deposition and the dual-pulse experiments are in good agreement with the theory.
PACS 52.38.Mf; 79.20.Ds; 61.80.Ba 相似文献
6.
We describe a new technique to measure the UV/visible absorption spectrum of the ablated material during the laser pulse.
The technique utilizes the continuum emission from one laser produced plasma as a light source to measure the absorption properties
of a second laser produced plasma which is formed on a semi-transparent target with an array of 40 μm holes. A 6 ns, 1064
nm laser was used to ablate a Ag target and the plasma absorption was measured in the range 450–625 nm for a laser fluence
of 1 J cm−2. The total absorption cross-section is (0.5–1.5)×10−17 cm2 in the range 450–540 nm. By comparing the measured absorption with a calculation using the plasma spectroscopy code FLYCHK
it can be concluded that, in the wavelength region examined here, the absorption is mainly due to bound-bound transitions. 相似文献
7.
Coherent terahertz radiation in a widely step-tunable range of 72.3–2706 μm (0.11–4.15 THz) has been generated in GaAs crystal
by difference-frequency generation using one CO2 laser with dual-wavelength output. The peak power of THz pulse reaches 35 W at the wavelength of 236.3 μm, which corresponds
to a pulse energy of 2.1 μJ. An average power of 10 μW has been achieved when working repetitively. This efficient terahertz
radiation source is more compact and widely tunable than other THz sources pumped by CO2 laser. 相似文献
8.
Csaba László Sajti Svea Petersen Ana Menéndez-Manjón Stephan Barcikowski 《Applied Physics A: Materials Science & Processing》2010,101(2):259-264
In-situ functionalization of gold nanoparticles with fluorophore-tagged oligonucleotides is studied by comparing femtosecond
laser ablation in stationary liquid and in biomolecule flow. Femtosecond laser pulses induce significant degradation to sensitive
biomolecules when ablating gold in a stationary solution of oligonucleotides. Contrary, in-situ conjugation of nanoparticles
in biomolecule flow considerably reduces the degree of degradation studied by gel electrophoresis and UV–Vis spectrometry.
Ablating gold with 100 μJ femtosecond laser pulses DNA sequence does not degrade, while the degree of fluorophore tag degradation
was 84% in stationary solution compared to 5% for 1 mL/min liquid flow. It is concluded that femtosecond laser-induced degradation
of biomolecules is triggered by absorption of nanoparticle conjugates suspended in the colloid and not by ablation of the
target. Quenching of nanoparticle size appears from 0.5 μM biomolecule concentration for 0.3 μg/s nanoparticle productivity
indicating the successful surface functionalization. Finally, increasing the liquid flow rate from stationary to 450 mL/min
enhances nanoparticle productivity from 0.2 μg/s to 1.5 μg/s, as increasing liquid flow allows removal of light absorbing
nanoparticles from the ablation zone, avoiding attenuation of subsequent laser photons. 相似文献
9.
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
10.
T. Kobayashi T. Kato Y. Matsuo M. Kurata-Nishimura Y. Hayashizaki J. Kawai 《Applied Physics A: Materials Science & Processing》2008,92(4):777-780
By ablating solid C60 with a laser pulse, we observe various processes such as the prompt- and the delayed-ionization of C60, the fragmentation into molecular ions and the formation of cluster ions. We found these processes show distinct dependences
on the temporal pulse width, the power and the wavelength of the ablation laser. From the observations, we could confirm efficient
coupling of laser energy to C60 through the molecular absorption even with a laser pulse width less than the electron-phonon coupling time of the C60 molecule. 相似文献
11.
E. Cappelli C. Scilletta G. Mattei V. Valentini S. Orlando M. Servidori 《Applied Physics A: Materials Science & Processing》2008,93(3):751-758
The structure of thin films deposited by pulsed laser ablation (PLD) is strongly dependent on experimental conditions, like
laser wavelength and fluence, substrate temperature and pressure. Depending on these parameters we obtained various kinds
of carbon materials varying from dense, mainly tetrahedral amorphous carbon (ta-C), to less compact vertically oriented graphene
nano-particles.
Thin carbon films were grown by PLD on n-Si 〈100〉 substrates, at temperatures ranging from RT to 800°C, from a rotating graphite target operating in vacuum. The laser ablation of the graphite target was performed by a UV pulsed ArF excimer laser (λ=193 nm) and a pulsed Nd:YAG laser, operating in the near IR (λ=1064 nm).
The film structure and texturing, characterised by X-ray diffraction analysis, performed at grazing incidence (GI-XRD), and
the film density, evaluated by X-ray reflectivity measurements, are strongly affected both by laser wavelength and fluence
and by substrate temperature.
Micro-Raman and GI-XRD analysis established the progressive formation of aromatic clusters and cluster condensation into vertically
oriented nano-sized graphene structures as a direct function of increasing laser wavelength and deposition temperature. The
film density, negatively affected by substrate temperature and laser wavelength and fluence, in turn, results in a porous
bulk configuration and a high macroscopic surface roughness as shown by SEM characterisation. These structural property modifications
induce a relevant variation also on the emission properties of carbon nano-structures, as evidenced by field emission measurements.
This work is dedicated to our friend Giorgio who passed away 20th August. 相似文献
12.
Hidetoshi Nakano Katsuya Oguri Yasuaki Okano Tadashi Nishikawa 《Applied Physics A: Materials Science & Processing》2010,101(3):523-531
We investigated spatiotemporal evolution of expanding ablation plume of aluminum created by a 100-fs, 1014–1015-W/cm2 laser pulse. For diagnosing dynamic behavior of ablation plume, we employed the spatiotemporally resolved X-ray absorption
spectroscopy (XAS) system that consists of a femtosecond-laser-plasma soft X-ray source and a Kirkpatrick–Baez (K–B) microscope.
We successfully assigned the ejected particles by analyzing structure of absorption spectra near the L
II,III absorption edge of Al, and we clarified the spatial distribution of Al+ ions, Al atoms, and liquid droplets of Al in the plume. We found that the ejected particles strongly depend the irradiated
laser intensity. The spatial distribution of atomic density and the expansion velocity of each type of particle were estimated
from the spatiotemporal evolution of ablation particles. We also investigated a temperature of the aluminum fine particles
in liquid phase during the plume expansion by analyzing the slope of the L
II,III absorption edge in case of 1014-W/cm2 laser irradiation where the nanoparticles are most efficiently produced. The result suggests that the ejected particles travel
in a vacuum as a liquid phase with a temperature of about 2500 to 4200 K in the early stage of plume expansion. 相似文献
13.
A. K. Chaudhary A. M. Rudra P. Kumbhakar G. C. Bhar 《Journal of Applied Spectroscopy》2007,74(4):571-577
We report a technique for the efficient generation of tunable coherent deep UV radiation and its application in studies of
RDX and TNT at the ppm level on the basis of their absorption characteristics. The obtained experimental absorption data are
compared with conventional spectrophotometric data. The UV radiation in the range 200–260 nm has been generated by the type-I
noncollinear third harmonic of the dye laser radiation (600–700 nm) and also by sum frequency mixing (SFM) of Nd:YAG output
(1064 nm) with the second harmonic of the dye laser in β-barium borate (BBO) crystal. The maximum conversion efficiency of
the generated signal is estimated to be 57.5% at λ = 218.9 nm wavelength. Apart from measurements of the absorbance of RDX
and TNT at different concentrations in their respective solutions, the minimum detection concentrations have also been ascertained.
The estimated minimum detectable concentration of RDX is 8.47·10−9 M, whereas that for TNT is 35.7·10−9 M. The data were obtained using only ∼100 μJ/pulse of laser energy.
Published in Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 516–521, July–August, 2007. 相似文献
14.
M. Yüksek A. Elmali M. Karabulut G. M. Mamedov 《Applied physics. B, Lasers and optics》2010,98(1):77-81
P type-GaSe and 0.01 at% Ge doped GaSe crystal were grown using the conventional Bridgman–Stochbarger method from a stoichiometric
mixture of starting materials in quartz ampoules, and the nonlinear absorption properties of both crystals have been studied
by using an open aperture Z-scan technique under 1064 nm wavelength with 4 ns or 65 ps pulse durations. GaSe crystal exhibits
two-photon absorption (TPA) at all input irradiances. On the other hand, at low input irradiance the Ge doped GaSe crystal
exhibits saturable absorption (SA). At higher input irradiances TPA becomes dominant. A monotonic increase of the nonlinear
absorption coefficient with increasing laser pulse duration from 65 ps to 4 ns is observed for the GaSe and Ge doped GaSe
crystals. 相似文献
15.
T.V. Kononenko S.V. Garnov S.M. Pimenov V.I. Konov V. Romano B. Borsos H.P. Weber 《Applied Physics A: Materials Science & Processing》2000,71(6):627-631
Laser ablation of thin TiN films deposited on steel substrates has been studied under wide-range variation of irradiation
conditions (pulsewidth, wavelength, energy density and spot size). It has been demonstrated that both picosecond (150–300 ps)
and nanosecond (5–9 ns) laser pulses were suitable for controllable ablation and microstructuring of a 1-μm-thick TiN film
unlike longer 150-ns pulses. The ablation rate was found to be practically independent of the wavelength (270–1078 nm) and
pulsewidth (150 ps–9 ns), but it increased substantially when the size of a laser spot was reduced from 15–60 μm to 3 μm.
The laser ablation technique was applied to produce microstructures in the thin TiN films consisting of microcraters with
a typical size of 3–5 μm in diameter and depth less than 1 μm. Tests of lubricated sliding of the laser-structured TiN films
against a steel ball showed that the durability of lubricated sliding increased by 25% as compared to that of the original
TiN film.
Received: 28 July 1999 / Accepted: 17 April 2000 / Published online: 20 September 2000 相似文献
16.
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
17.
Yuji Utsunomiya Takashi Kajiwara Takashi Nishiyama Kunihito Nagayama Shiro Kubota Motonao Nakahara 《Applied Physics A: Materials Science & Processing》2010,101(1):137-141
The pulse laser ablation of a liquid surface in air when induced by laser irradiation through a liquid medium has been experimentally
investigated. A supersonic liquid jet is observed at the liquid–air interface. The liquid surface layer is driven by a plasma
plume that is produced by laser ablation at the layer, resulting in a liquid jet. This phenomenon occurs only when an Nd:YAG
laser pulse (wavelength: 1064 nm) is focused from the liquid onto air at a low fluence of 20 J/cm2. In this case, as Fresnel’s law shows, the incident and reflected electric fields near the liquid surface layer are superposed
constructively. In contrast, when the incident laser is focused from air onto the liquid, a liquid jet is produced only at
an extremely high fluence, several times larger than that in the former case. The similarities and differences in the liquid
jets and atomization processes are studied for several liquid samples, including water, ethanol, and vacuum oil. The laser
ablation of the liquid surface is found to depend on the incident laser energy and laser fluence. A pulse laser light source
and high-resolution film are required to observe the detailed structure of a liquid jet. 相似文献
18.
Results are presented on the surface damage thresholds of ITO thin films induced by single- and multi-pulse laser irradiation
at a pulse duration of 10 ps and a wavelength of 1064 nm. For multi-pulse ablation the incubation effect results in a reduction
of the damage threshold, especially apparent at low pulse numbers and very small film thicknesses. The incubation effect attributes
to the accumulation of defect sites and/or the storage of thermal stress-strain energy induced by the incident laser pulses.
An incubation coefficient of S=0.82 has been obtained which is independent on the film thickness in the range of 10–100 nm. In practical applications, the
incubation effect determines the laser patterning structure of ITO films while increasing the pulse overlapping rate. The
width of the patterned line can be predicted by the proposed model involving the laser fluence, the overlapping rate and the
incubation coefficient. 相似文献
19.
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
20.
N. Muhammad D. Whitehead A. Boor W. Oppenlander Z. Liu L. Li 《Applied Physics A: Materials Science & Processing》2012,106(3):607-617
The demand for micromachining of coronary stents by means of industrial lasers rises quickly for treating coronary artery
diseases, which cause more than one million deaths each year. The most widely used types of laser for stent manufacturing
are Nd:YAG laser systems with a wavelength of 1064 nm with pulse lengths of 10−3–10−2 seconds. Considerable post-processing is required to remove heat-affected zones (HAZ), and to improve surface finishes and
geometry. Using a third harmonic laser radiation of picosecond laser (6×10−12 s pulse duration) in UV range, the capability of the picosecond laser micromachining of nitinol and platinum–iridium alloy
for coronary stent applications are presented. In this study dross-free cut of nitinol and platinum–iridium alloy tubes are
demonstrated and topography analysis of the cut surface is carried out. The HAZ characteristics have been investigated by
means of microscopic examinations and measurement of micro-hardness distribution near the cut zones. 相似文献