共查询到20条相似文献,搜索用时 15 毫秒
1.
Au nanorods dispersed in aqueous solution were prepared with the electrochemical method. The absorption spectrum shows two absorption peaks corresponding to the perpendicular and transverse surface plasma resonance absorption of the nanorods. The third-order optical nonlinear properties are investigated by Z-scans. The signs of the nonlinear absorption coemcient and refractive index are reversed as the intensity of incident laser increases, which is due to the shape change of the gold nanoparticles melted by the intense laser pulses. 相似文献
2.
A. L. Stepanov V. F. Valeev V. I. Nuzhdin I. A. Faizrakhmanov 《Physics of the Solid State》2009,51(9):1912-1918
The action of KrF excimer laser radiation on the composite material consisting of the silica glass with copper nanoparticles
is investigated as a function of the number of nanosecond laser pulses. Metal nanoparticles are synthesized by ion implantation.
It is established using optical reflectance measurements of composite layers that, at the initial stage, the irradiation leads
to the fragmentation of the largest nanoparticles. Then, after irradiation by several pulses, the particles become larger
due to the heating of the glass. The laser treatment for a longer time (several tens and hundreds of pulses) results in the
dissociation of nanoparticles into small clusters and individual atoms. The mechanisms responsible for the modification of
the composite material under high-power laser radiation are discussed. 相似文献
3.
A.?L.?Stepanov V.?F.?Valeev V.?I.?Nuzhdin V.?V.?Bazarov I.?A.?Fa?zrakhmanov 《Technical Physics》2009,54(10):1504-1510
The effect of KrF excimer laser radiation on a composite layer consisting of sodium-potassium silicate glass with silver nanoparticles
is studied as a function of the number of laser nanosecond pulses. The silver nanoparticles are synthesized by ion implantation.
The measured optical absorption of the composite layer demonstrates that the silver nanoparticle size decreases monotonically
as the number of laser pulses increases. Rutherford backscattering shows that laser annealing is accompanied by silver diffusion
into the bulk of the glass and partial metal evaporation from the sample surface. The detected decrease in the silver nanoparticle
size is discussed in terms of simultaneous melting of silver nanoparticles and the glass matrix due to the absorption of laser
radiation. 相似文献
4.
A. L. Stepanov 《Optics and Spectroscopy》2011,111(2):215-219
The effect of nanosecond excimer laser pulses on a composite layer of sodium-calcium silicate glass with silver nanoparticles
has been investigated. Nanoparticles were synthesized by ion implantation. Based on measuring the optical absorption and reflection
spectra of the composite layers, it is found that an increase in the number of laser pulses leads to a monotonic decrease
in the size of silver nanoparticles. However, laser irradiation with a longer duration leads to the growth of nanoparticles
with their subsequent destruction. The effects observed are discussed in terms of heating a glass composite layer as a result
of the effective absorption of laser radiation. 相似文献
5.
We show that photoionization of wide band gap silicate glasses by infrared ultrashort laser pulses can occur without laser-induced
damage. Two glasses are studied, fused silica and a multi-component silicate photo-thermo-refractive (PTR) glass. Experiments
are performed by low numerical aperture focusing of ultrashort laser pulses (100 fsec<τ<1.5 psec) at the wavelengths 780 nm, 1430 nm, and 1550 nm. Filaments form inside both glasses and are visibly observable
due to intrinsic luminescence. Keldysh’s theory of nonlinear photoionization is used to model the formation of filaments and
values of about 1013 W cm−2 for the laser intensity and 1019 cm−3 for the free electron density are estimated for stable filaments to arise. Laser-induced damage is studied by the generation
of a third harmonic from an interface created between a damage site and the surrounding glass matrix. It is found that third
harmonic generation occurs only after several thousands of laser shots indicating that damage is not a single-shot phenomena.
The ability to photoionize PTR glass without damage by ultrashort laser pulses offers a new approach for fabricating diffractive
optical elements in photosensitive glass. 相似文献
6.
Gaofang Li Xin Xue Xian Lin Sannan Yuan Naiyun Tang Fenghong Chu Haoyang Cui Guohong Ma 《Applied Physics A: Materials Science & Processing》2014,114(1):45-50
The unique optical properties of nanoparticles are highly sensitive in respect to particle shapes, sizes, and localization on a sample. This demands for a fully controlled fabrication process. The use of femtosecond laser pulses to generate and transfer nanoparticles from a bulk target towards a collector substrate is a promising approach. This process allows a controlled fabrication of spherical nanoparticles with a very smooth surface. Several process parameters can be varied to achieve the desired nanoparticle characteristics. In this paper, the influence of two of these parameters, i.e. the applied pulse energy and the laser beam shape, on the generation of Si nanoparticles from a bulk Si target are studied in detail. By changing the laser intensity distribution on the target surface one can influence the dynamics of molten material inducing its flow to the edges or to the center of the focal spot. Due to this dynamics of molten material, a single femtosecond laser pulse with a Gaussian beam shape generates multiple spherical nanoparticles from a bulk Si target. The statistical properties of this process, with respect to number of generated nanoparticles and laser pulse energy are investigated. We demonstrate for the first time that a ring-shaped intensity distribution on the target surface results in the generation of a single silicon nanoparticle with a controllable size. Furthermore, the generated silicon nanoparticles presented in this paper show strong electric and magnetic dipole resonances in the visible and near-infrared spectral range. Theoretical simulations as well as optical scattering measurements of single silicon nanoparticles are discussed and compared. 相似文献
7.
The sizes, shapes, and growth rates of gold and silver nanoparticles stabilized with polyvinylpyrrolidone in water can be
controlled by using picosecond laser pulses. The nucleation of small metal clusters formed with NaBH4 addition to produce nanoparticles takes two months with aging but 30 min with laser irradiation. Laser pulses can also induce
nanoparticles to have narrow size and shape distribution or to undergo aggregation into much larger particles. The latter
process is more likely found when the metal is silver or the irradiation wavelength is short. Laser-induced growth and shape
transformation processes are explained in terms of BH4
− depletion, metal fusion, and electron ejection followed by disintegration. 相似文献
8.
A third-order correlator suitable for detailed shape measurements of picosecond laser pulses has been developed. The working principle in both the single shot and the scanning mode is based on detection of the phase-matched difference frequency non-collinear generated signal in a non-linear crystal. This third-order OPA correlator was applied for the characterization of the specifically shaped picosecond laser pulses from the MBI CPA Nd: glass laser system. 相似文献
9.
The 3D shape of Ag nanoparticles in glass irradiated by fs laser pulses is investigated by optical spectroscopy. It is shown that in general spheroids are produced with their symmetry axis oriented along the direction of the linear laser polarization. Depending on the actual irradiation conditions, oblate or prolate spheroids are obtained. The halo of small Ag clusters and Ag ions around the reshaped particles causes a redshift of the surface plasmon resonances via refractive index increase. 相似文献
10.
M. Merschdorf W. Pfeiffer A. Thon S. Voll G. Gerber 《Applied Physics A: Materials Science & Processing》2000,71(5):547-552
Two-photon photoemission spectroscopy using femtosecond laser pulses is used to investigate the excitation and decay mechanisms
of the surface plasmon resonance in Ag nanoparticles grown on graphite. The resonant excitation of this collective excitation
leads to a two-orders-of-magnitude-enhanced two-photon photoemission yield from a graphite surface with Ag nanoparticles compared
to the yield from pure graphite. From the shape of the photoemission spectra, the polarization dependence of the photoemission
yield and the excitation probabilities for different excitation pathways we conclude that excitation with 400-nm femtosecond
laser pulses leads to the coherent multiple excitation of the surface plasmon in the Ag nanoparticles. This multiply excited
plasmon mode can decay via the coupling to a single-particle excitation leading to the emission of an electron if its final
state is located in the continuum. The surface plasmon in metallic nanoparticles is a model system to investigate collective
excitations in multiphoton processes.
Received: 26 June 2000 / Accepted: 2 September 2000 / Published online: 12 October 2000 相似文献
11.
We report on space-selective co-precipitation of silver and gold nanoparticles in Ag+, Au3+ co-doped silicate glasses by irradiation of femtosecond laser pulses and subsequent annealing at high temperatures. The color of the irradiated area in the glass sample changed from yellow to red with the increase of the annealing temperature. The effects of average laser power and annealing temperature on precipitation of the nanoparticles were investigated. A reasonable mechanism was proposed to explain the observed phenomena. 相似文献
12.
Ultrashort pulsed laser ablation in vacuum of different targets was performed in order to investigate the possibility of producing nanoparticles with controlled size and shape. A systematic morphology characterization of deposited products was performed for nickel and silicon as a function of laser pulse intensity and wavelength, at a fixed pulse repetition rate. The nanoparticles were investigated by atomic force microscopy, and clear trends for their size and shape anisotropy were evidenced. The best conditions to obtain nanosized particles of oblate ellipsoidal shape, with the minor axis below 10 nm, were determined in the case of nickel targets. Our results show that ultrashort pulse laser deposition can be considered as an interesting technique for the tailoring of nanogranular films with the desired particles dimension and shape, according to the peculiar properties required in specific applications. Moreover, the preliminary features are very promising from the point of view of the production of magnetoresistive films with specific anisotropy. 相似文献
13.
M. Gedvilas G. Račiukaitis K. Regelskis 《Applied Physics A: Materials Science & Processing》2008,93(1):203-208
Self-organization of chromium on glass was observed during laser ablation of the metal film with partially overlapping laser
pulses. The beam of a nanosecond pulse laser tightly focused to a line was applied to the back-side ablation of the chromium
thin film on a glass substrate. While the line ablated with a single laser pulse had sharp edges on both sides with ridges
of the melted metal, the use of partially overlapping pulses formed a complicated structure made of the metal remaining from
the ridges. Regular structures of ripples were developed in a certain range of laser fluence and pulse overlap. The ripple
period could be controlled from 2.5 to 4 μm by variation of the processing parameters. Various experimental techniques were
applied to test the structures, and different models of the ripple formation in the thin metal film were considered. The initial
quasi-periodical formation started because of dewetting of thin liquid metal films on the glass substrate after its melting.
Similar to the evaporation of liquid films, the small perturbation in the ridge thickness was able to induce instability in
evaporation of the thin melted metal film. Freezing of the nonequilibrium state between laser pulses was one of the stabilizing
factors in self-organization of the metal. 相似文献
14.
V. Iannotti G. Ausanio C. Campana F. D’Orazio C. Hison F. Lucari L. Lanotte 《Journal of magnetism and magnetic materials》2008
Pulsed laser deposition (uPLD) in vacuum by means of subpicosecond laser pulses is a powerful, versatile technique for the production of films constituted by nanoparticles. On impact with the deposition substrate, the nanodrops ejected from the target assume an oblate ellipsoidal shape, solidifying with the major cross-section parallel to the substrate plane. These features and the difficult coalescence among the deposited nanoparticles are peculiar characteristics specific to the films obtained by uPLD. In the case of magnetic nanoparticle films obtained by means of this technique, a magnetization isotropy in the film plane and a hard magnetization axis orthogonal to the film plane are expected. This simple assumption, generated by the specific shape and orientation of the deposited nanoparticles, was not experimentally verified up to now. The present investigation represents the first experimental validation of magnetic anisotropy, determined by the peculiar morphology and topology of the constituent particles, in the uPLD NixSi100−x nanoparticle films. The in-plane isotropic magnetization behaviour, as well as the presence of a hard magnetization axis perpendicular to the sample surface were demonstrated for all investigated films. The difficult coalescence among the magnetic nanoparticles, even at high Ni volume fractions, is confirmed by the behaviour of the initial magnetization curve, typical for single-domain nanoparticles systems. 相似文献
15.
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
16.
Self-Assembled Quasi-Periodic Voids in Glass Induced by a Tightly Focused Femtosecond Laser
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Multiple refocusing of a tightly focused femtosecond laser due to the dynamic transformation between self-focusing and self-defocusing is employed to provide a novel method to produce quasi-periodic voids in glass. It is found that the diameter or the interval of the periodic voids increases with the increasing pulse energy of the laser. The detailed course for producing periodic voids is discussed by analysing the damaged track induced by the tightly focused femtosecond laser pulses. It is suggested that this periodic structure has potential applications in fabrication of three-dimensional optical devices. 相似文献
17.
Yang Liao Bin Zeng Lingling Qiao Lianqing Liu Koji Sugioka Ya Cheng 《Applied Physics A: Materials Science & Processing》2014,114(1):223-230
Recently, femtosecond laser direct writing in porous glass is emerging as a powerful technique for building arbitrary 3D hollow micro/nanostructures in bulk glass materials. In this study, we investigate the pulse duration dependence of laser intensity window for inducing a single nanocrack inside porous glass by femtosecond laser direct writing. We find that the window for a single nanocrack increases with the pulse duration, while the roughness of side walls in the nanocracks becomes higher for pulses longer than ~300 fs. When the femtosecond laser pulses of an optimized duration of ~200 fs are chosen, a sufficiently broad range of laser intensity (~44 % of the structuring threshold) for creating a single nanocrack can be obtained, while smooth sidewalls required by nanofluidic applications can still be maintained. The reported results will be beneficial not only for the development of the 3D femtosecond laser micro/nanostructuring techniques, but also for gaining a deeper understanding of the physical mechanism behind the nanograting formation induced by femtosecond laser irradiation in glass and other transparent materials. 相似文献
18.
Thin films of silver nanoparticles deposited in vacuum by pulsed laser ablation using a YAG:Nd laser
J.C. Alonso R. Diamant P. Castillo M.C. Acosta-García N. Batina E. Haro-Poniatowski 《Applied Surface Science》2009,255(9):4933-4937
We report the deposition of thin films of silver (Ag) nanoparticles by pulsed laser ablation in vacuum using the third line (355 nm) of a YAG:Nd laser. The nanostructure and/or morphology of the films was investigated as a function of the number of ablation pulses, by means of transmission electron microscopy and atomic force microscopy. Our results show that films deposited with a small number of ablation pulses (500 or less), are not continuous, but formed of isolated nearly spherical Ag nanoparticles with diameters in the range from 1 nm to 8 nm. The effect of increasing the number of pulses by one order of magnitude (5000) is to increase the mean diameter of the globular nanoparticles and also the Ag areal density. Further increase of the number of pulses, up to 10,000, produces the formation of larger and anisotropic nanoparticles, and for 15,000 pulses, quasi-percolated Ag films are obtained. The presence of Ag nanoparticles in the films was also evidenced from the appearance of a strong optical absorption band associated with surface plasmon resonance. This band was widened and its peak shifted from 425 nm to 700 nm as the number of laser pulses was increased from 500 to 15,000. 相似文献
19.
R. A. Ganeev 《Optics and Spectroscopy》2018,124(4):521-535
We review the studies of the modifications of harmonic spectra from laser-produced plasmas. The substantial spectral broadening and blue shift of the harmonics generating in the laser plasma during transformation of the spectrum of the laser radiation formed the filaments upon passage of femtosecond pulses through the argon gas is analyzed. We also discuss the studies of harmonic spectra variations that occur as a result of the passage of the laser pulses through the carbon- and metal-containing plasmas at the variable density of ablated species and intensity of driving pulse. To show other type of modulation of harmonic emission spectra, the plasmas containing the small molecules of silver produced during ablation of the bulk silver and silver nanoparticles at the conditions suitable for efficient harmonic generation of the ultrashort pulses propagating through the laser-produced plasmas were analyzed. The time-of-flight mass-spectroscopy studies of plasmas confirmed the presence of these species in plasmas. 相似文献
20.
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