共查询到20条相似文献,搜索用时 15 毫秒
1.
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
2.
Based on a computer simulation, the self-focusing of an axially symmetric beam in a cubic nonlinear medium under the anomalous dispersion conditions is studied with the account for the time dispersion of nonlinear response, which manifests for femtosecond pulses. It is shown that, at a certain value of the parameter of linear modulation of the pulse (or of its chirp), the dispersion of nonlinear response can lead either to the suppression of formation of a nonlinear focus and to the possibility of formation of optical shock waves in time or even to a change in the regime of the beam self-action owing to the action of the local response, i.e., to the change from the self-focusing of the beam to the regime of its defocusing. 相似文献
3.
R. M. Arkhipov M. V. Arkhipov I. Babushkin N. N. Rosanov 《Optics and Spectroscopy》2016,121(5):758-764
In the regime of coherent interaction of short optical pulses with a resonant medium, which is implemented with a pulse duration shorter than the relaxation times in the medium, the formation of population gratings can occur without overlapping the pulses therein. In this case, there are new possibilities for controlling optical pulses, which are especially pronounced for extremely short pulses. It is shown that, with the proper choice of the parameters of a sequence of extremely short optical pulses, not only the formation of population gratings, but also their erasure are possible. It is demonstrated that this effect can be used for the creation of an ultrahigh-speed optical deflector. 相似文献
4.
We show that the propagation of short pulses in optical lines with strong dispersion management is described by an integrable
Hamiltonian system. The leading nonlinear effect is the formation of a collective dispersion which is a result of the interaction
of all pulses propagating along the line.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 9, 573–576 (10 November 1999)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
5.
6.
Among heterogeneously catalyzed chemical reactions, the CO oxidation on the Pt(110) surface under vacuum conditions offers probably the greatest wealth of spontaneous formation of spatial patterns. Spirals, fronts, and solitary pulses were detected at low surface temperatures (T<500 K), in line with the standard phenomenology of bistable, excitable, and oscillatory reaction-diffusion systems. At high temperatures (T greater, similar 540 K), more surprising features like chemical turbulence and standing waves appeared in the experiments. Herein, we study a realistic reaction-diffusion model of this system, with respect to the latter phenomena. In particular, we deal both with the influence of global coupling through the gas phase on the oscillatory reaction and the possibility of wave instabilities under excitable conditions. Gas-phase coupling is shown to either synchronize the oscillations or to yield turbulence and standing structures. The latter findings are closely related to clustering in networks of coupled oscillators and indicate a dominance of the global gas-phase coupling over local coupling via surface diffusion. In the excitable regime wave instabilities in one and two dimensions have been discovered. In one dimension, pulses become unstable due to a vanishing of the refractory zone. In two dimensions, turbulence can also emerge due to spiral breakup, which results from a violation of the dispersion relation. 相似文献
7.
Yu. Ya. Volkolupov A. N. Dovbnya V. V. Zakutin M. A. Krasnogolovets N. G. Reshetnyak V. P. Romas’ko 《Technical Physics》2001,46(9):1196-1198
The formation of an electron layer and the generation of an electron beam in magnetron guns where secondary emission is triggered by nanosecond pulses are studied. In the guns with small cross sizes, hollow electron beams with an outer diameter of 3–6 mm are generated. The beam current is 1–2 A, and the cathode voltage is 5–7 kV. Results obtained indicate that the generation of nanosecond beam-current pulses is a possibility. 相似文献
8.
A new mechanism for the transformation of video pulses into radio pulses during their propagation along a nonlinear transmission line with spatial dispersion—synchronism with a backward wave—is considered. Numerical simulations demonstrate that a substantial advantage of this mechanism over the interaction with a forward wave is the possibility of generating longer radio pulses at higher frequencies. 相似文献
9.
A. A. Frolov A. V. Borodin M. N. Esaulkov I. I. Kuritsyn A. P. Shkurinov 《Journal of Experimental and Theoretical Physics》2012,114(6):893-905
A theory is developed for calculating the spectrum and the shape of a terahertz wave packet from the temporal profile of the energy of the second harmonic of the laser field generated during nonlinear interaction of laser and terahertz pulses in an optical-breakdown plasma. The spectral and temporal characteristics of the second-harmonic envelope and a terahertz pulse are shown to coincide only for short laser pulses. For long laser pulses, the second-harmonic spectral line shifts to the red and its temporal profile is determined by the time integral of the electric field of terahertz radiation. 相似文献
10.
《中国光学快报(英文版)》2015,(3)
Filamentation-induced water condensation and snow formation are investigated using laser pulses with different chirps and pulse widths. Chirped pulses result in the laser filamentation with different spatial lengths and intensities, which has a great impact on airflow motion and snow formation. The experiments show that snow formation mainly relates to the filament intensity distribution. Negative chirped pulses produce a greater amount of snow because of higher intensity inside the filaments as compared with the positive chirped pulses. 相似文献
11.
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
12.
Ramsey schemes with pulses of different lengths and with a composite pulse have been analyzed taking into account a finite width of the laser line and spontaneous relaxation of atomic levels. The optimal parameters of pulses corresponding to the maximum suppression of the excitation-related shift and the maximum resonance amplitude have been found for both schemes. According to the numerical results, spontaneous relaxation of the atomic levels and a finite width of the laser line must be taken into account in the calculation of the optimal parameters of the excitation pulses. The Ramsey scheme with a composite pulse is less sensitive to fluctuations of the Rabi frequency than the scheme with pulses of different lengths. 相似文献
13.
We investigate dynamics of the formation of high-power ultrashort self-similar light pulses (similaritons) in a fiber laser in the regime of positive dispersion. The physical factors limiting the energy and the pulse width of such pulses are revealed. We specify regimes where a laser system based on an ytterbium-doped fiber can generate self-similar pulses with an energy of about 80 nJ compressible to a pulse width of about 150 fs through extracavity linear chirp compensation. 相似文献
14.
Experimental results on two-pulse generation and transportation of high-current relativistic electron beams (REBs) through
the gaseous medium of a plasmochemical reactor (PR) are presented. The generation of two consecutive high-current REB pulses
with a duration of 60 ns was achieved at the Tonus accelerator with modified schemes of high-voltage pulse formation. The
first version of the formation scheme enabled pulse powers of 2 and 4.0–9.6 GW with a time interval between the pulses of
500 ns. The second version enabled one to generate pulses with powers of 1.8 and 16 GW and time interval between the pulses
of 160 μs. The transportation parameters of an REB injected into a 1.4-m-long PR filled with an N2: O2 gas mixture are studied. The conductance of the plasma produced under the action of the electron beams is measured. It is
shown that the schemes proposed provide more efficient (by 35–45%) transportation of the REBs in the reactor volume as compared
to single-pulse high-current REBs of the same power and pulse duration. 相似文献
15.
Nonlinear propagation of longitudinal-transverse acoustic pulses down to a length of one cycle (video pulses) in a low-temperature paramagnetic crystal in the direction parallel to an external magnetic field is investigated theoretically. The case of a crystal with paramagnetic impurity ions with effective S=1/2 spin is considered. It is shown that, due to spin-phonon interaction, two-component acoustic pulses can propagate in the form of high-power quasi-solitons. Conditions are determined for the formation of exponentially localized subsonic rational solitons which propagate with a velocity higher than the velocity of transverse sound and which have a transverse component with a rotating plane of polarization. 相似文献
16.
Improving the resolution and the uniformity of AFM tip induced oxide patterns with pulsed voltages 总被引:1,自引:0,他引:1
Ziyong Shen Hui Sun Shimin Hou Xingyu Zhao Zengquan Xue 《Applied Surface Science》2004,230(1-4):340-344
Oxide line patterns were fabricated on the surface of titanium (Ti) film using atomic force microscopy (AFM) tip induced local oxidation technique. The growth behavior of the oxide under static voltages was studied. It was found the lateral growth of the oxide experienced two stages and the growth rate at the initial stage was very high. Pulsed voltages were employed and their effects on the controlling of the oxidation dynamics were examined. The results indicated that the high lateral and vertical growth rates of oxide at the initial stage could be suppressed with pulsed voltages. A minimum line width of 8 nm and highly uniform patterns were obtained with optimized voltage pulses. These results indicated that applying pulsed voltage is an effective method for improving both the resolution and the uniformity of the fabricated structures with scanning probe microscopy (SPM) tip induced local oxidation technique. 相似文献
17.
A new type of delay line intended for soliton pulses is proposed. As a nonlinear medium, a semiconductor superlattice is taken. Solitons that propagate along the superlattice layers are confined in cells bounded by transverse inhomogeneity layers. Solitons are confined and released with the help of an external electric current passing inside the cell. 相似文献
18.
Wang Y Granados E Larotonda MA Berrill M Luther BM Patel D Menoni CS Rocca JJ 《Physical review letters》2006,97(12):123901
We demonstrate the generation of an intense soft-x-ray-laser beam by saturated amplification of high harmonic seed pulses in a dense transient collisional soft-x-ray-laser plasma amplifier created by heating a titanium target. Amplification in the 32.6 nm line of Ne-like Ti generates laser pulses of subpicosecond duration that are measured to approach full spatial coherence. The peak spectral brightness is estimated to be approximately 2 x 10(26) photons/(s mm(2) mrad(2) 0.01% bandwidth). The scheme is scalable to produce extremely bright lasers at very short wavelengths with full temporal and spatial coherence. 相似文献
19.
The applicability of a material-treatment laser pulse in non-destructive evaluations 总被引:1,自引:0,他引:1
A practical optodynamic study was performed to determine the usability of different lengths of laser pulses for the generation of ultrasonic transients in a solid material. The aim of the study was to evaluate the possibility of a dual use for a laser pulse-for laser material processing, on the one hand, and for the ultrasonic wave generation on the other-with both processes being combined on the same production line. The propagation of the laser-generated ultrasonic waves is evaluated by detecting and measuring with a PID-controlled stabilized interferometer. Thus, both systems provided the basic tools, the generation and detection of ultrasonic waves, for an ultrasonic, laser-based, non-destructive material evaluation. The ultrasonic transients generated by 'classical' nanosecond laser pulses were compared with the transients generated by industrial laser pulses with a duration of a few tenths of a microsecond. The experimental results are compared with the results of a time-of-flight analysis that also involved part of a mode-conversion analysis for both regimes in a layered material structure. The differences between the two waveforms were assessed in terms of their visibility, wavelength and resolution. The limit values were calculated and estimated for the laser-pulse parameters, when such pulses are intended for use in an ultrasonic, laser-based, non-destructive evaluation. The possibility of using an industrial marking laser for laser ultrasound generation is thus demonstrated. 相似文献
20.
L. M. Vasilyak S. P. Vetchinin D. N. Polyakov V. E. Fortov 《Journal of Experimental and Theoretical Physics》2002,94(3):521-524
The formation and destruction of ordered dust structures in glow discharges are investigated experimentally. The initial construction phase of an ordered structure is related to the construction of its cooperative field and is determined by the number of particles and by the existence of crystallization centers. After the structure has been constructed, it influences the local plasma properties and the discharge current-voltage characteristics. The recovery of the structure after weak exposure takes place at local equilibrium, while, after intense exposure to high-voltage nanosecond pulses, it is determined by the fluctuation level and the degree of chaotization in the system. 相似文献