共查询到20条相似文献,搜索用时 62 毫秒
1.
O.G. Kosareva N.A. Panov N. Akozbek V.P. Kandidov Q. Luo S.A. Hosseini W. Liu J.-F. Gravel G. Roy S.L. Chin 《Applied physics. B, Lasers and optics》2006,82(1):111-122
We demonstrate a three orders of magnitude increase and stability in the backscattered fluorescence signal from nitrogen molecules
by terawatt femtosecond laser pulse induced air filaments using a new method. The method is based on squeezing the initial
beam diameter using a telescope. The effect of laser shot-to-shot fluctuations was included in numerical simulations by a
random distribution of the initial intensity in both squeezed and non-squeezed beams. Statistical processing of the simulation
results shows that the average diameter of plasma channels as well as the total amount of free electrons generated in a bunch
of multiple filaments in air is larger in the squeezed beam. Shot-to-shot stability of the simulated plasma density increases
in the squeezed beam. The change of this plasma density with propagation distance is in good qualitative agreement with the
change of the range-corrected nitrogen fluorescence signal with distance.
PACS 42.65.Jx; 42.60.Jf; 42.68.Ay; 42.68.Wt 相似文献
2.
V. Yu. Fedorov V. P. Kandidov O. G. Kosareva N. Akozbek M. Scalora S. L. Chin 《Laser Physics》2006,16(8):1227-1234
The effect of transverse elliptical intensity distribution on multiple filament formation in a femtosecond laser pulse is numerically studied. Two types of filament control are demonstrated. First, the beginning of filamentation can be varied by changing the degree of ellipticity. Second, random multiple filaments can be arranged in a spatial order predetermined by the specific shape of the ellipse. The latter is valid for pulses with a peak power more than ten times higher than the critical power for self-focusing in the medium. 相似文献
3.
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
4.
The propagation of optical vortices nested in broadband femtosecond laser beams was studied both numerically and experimentally. Based on the nonlinear Schrödinger equation, the dynamics of different multiple-vortex configurations with varying topological charge were modelled in self-focussing and self-defocussing Kerr media. We find a similar behavior in both cases regarding the vortex–vortex interaction. However, the collapsing background beam alters the propagation for a positive nonlinearity. Regimes of regular and possibly stable multiple filamentation were identified this way. Experiments include measurements on pairs of filaments generated in a vortex beam on an astigmatic Gaussian background with argon gas as the nonlinear medium. Spectral broadening of these filaments leads to a supercontinuum which spans from the visible range into the infrared. Recompression yields <19 fs pulses. Further optimization may lead to much better recompression. 相似文献
5.
Superhydrophobic surfaces fabricated by microstructuring of stainless steel using a femtosecond laser 总被引:1,自引:0,他引:1
Fabrication of superhydrophobic surfaces induced by femtosecond laser is a research hotspot of superhydrophobic surface studies nowadays. We present a simple and easily-controlled method for fabricating stainless steel-based superhydrophobic surfaces. The method consists of microstructuring stainless steel surfaces by irradiating samples with femtosecond laser pulses and silanizing the surfaces. By low laser fluence, we fabricated typical laser-induced periodic surface structures (LIPSS) on the submicron level. The apparent contact angle (CA) on the surface is 150.3°. With laser fluence increasing, we fabricated periodic ripples and periodic cone-shaped spikes on the micron scale, both covered with LIPSS. The stainless steel-based surfaces with micro- and submicron double-scale structure have higher apparent CAs. On the surface of double-scale structure, the maximal apparent CA is 166.3° and at the same time, the sliding angle (SA) is 4.2°. 相似文献
6.
The triggering and guiding of high voltage discharge by plasma filaments generated by 400 nm and 800 nm femtosecond laser were studied experimentally. The detailed diagnostics for characteristics of filaments, such as amount of free electrons, diameter and electron density, were performed using sonographic method, fluorescence imaging and resistivity measurement. A significant reduction of the breakdown voltage threshold due to the pre-ionization of the air gap by laser pulse filaments was observed. It is shown that the 400 nm laser pulses demonstrated stronger triggering ability than 800 nm laser pulse under same pulse energy. This behavior of 400 nm femtosecond pulse is connected to the rich population of highly excited particles in filaments. 相似文献
7.
Q. Luo S.A. Hosseini W. Liu J.-F. Gravel O.G. Kosareva N.A. Panov N. Aközbek V.P. Kandidov G. Roy S.L. Chin 《Applied physics. B, Lasers and optics》2005,80(1):35-38
This paper describes the effects observed during the propagation of intense femtosecond laser pulses in air following the modification of the laser beam diameter with a pair of convex–concave lenses placed/mounted in a telescopic configuration. We observed that by reducing the diameter of the beam the detected back-scattered nitrogen fluorescence from the filaments becomes more stable on a shot-to-shot basis while, for a larger beam size, greater fluctuations are observed that are not correlated to shot-to-shot fluctuations in the laser pulse energy. This result leads to a new method to control the fluorescence signal which can be very important in remote-sensing applications. PACS 42.65.Jx; 42.68.Ay; 42.68.Wt 相似文献
8.
We examine the nonlinear dynamics of femtosecond filaments in air at different pressures. Emphasis is placed on the changes in multiple filamentation patterns produced by terawatt laser pulses. Principal modifications induced by pressure variations apply to the onset distance, size, and number of the filaments inside the laser bundle. 相似文献
9.
Yoshiki Nakata Kunio Tsuchida Noriaki Miyanaga 《Optics and Lasers in Engineering》2009,47(7-8):847-849
Combined periodic structures composed of micron-sized periodic structure and nano-sized quasi periodic structure were generated on Ni–Ti target by multiple shots of interfering femtosecond laser beams. The micron-sized structure was generated by the interference pattern of four beams, and the nano-sized quasi period was generated due to the multiple shot effect of femtosecond laser. The structures were investigated in detail by two-dimensional fast Fourier transform (2D-FFT). The power spectra showed small spots and fuzzy spots due to precise period and quasi period, respectively. The most major size of the quasi periodic structure was 580 nm. 相似文献
10.
Since their discovery in the mid-1990s, ultrafast laser filaments in gases have been described as products of a dynamic balance between Kerr self-focusing and defocusing by free electric charges that are generated via multiphoton ionization on the beam axis. This established paradigm has been recently challenged by a suggestion that the Kerr effect saturates and even changes sign at high intensity of light and that this sign reversal, not free-charge defocusing, is the dominant mechanism responsible for the extended propagation of laser filaments. We report qualitative tests of the new theory based on electrical and optical measurements of plasma density in femtosecond laser filaments. Our results consistently support the established paradigm. 相似文献
11.
12.
Effective length of filaments measurement using backscattered fluorescence from nitrogen molecules 总被引:2,自引:0,他引:2
S.A. Hosseini Q. Luo B. Ferland W. Liu N. Aközbek G. Roy S.L. Chin 《Applied physics. B, Lasers and optics》2003,77(6-7):697-702
The effective length of self-induced long (100 meters) plasma filaments, generated by intense femtosecond near IR laser pulses in air, was measured remotely using a lidar technique. This technique is based on detecting the backscattered fluorescence signal from nitrogen molecules excited along the intense laser pulse propagation path. This opens up the possibility of measuring remotely long filaments extending over hundreds of meters in the atmosphere. PACS 42.65.Jx; 42.68.Ay; 42.68.Wt 相似文献
13.
The propagation of femtosecond laser pulses in turbulent air near the ground is analyzed. Confining to a power regime distinctly
above the critical power for self-focusing, i.e. P≈100P
cr, and concentrating on initial peak intensities around 2.5×1011W/cm2, the onset and early evolution of multiple filaments are addressed. Making use of the turbulence phase-screen method, numerical
simulations of the pulse propagation indicate that turbulence fields with spatial scales below 6 mm are able to induce the
onset of multifilamentation. An analytical linear plane wave perturbation model of the underlying modulation instability of
the pulse front is introduced in support of the computational results. By this means, insight into the amplification of an
initial perturbation of the pulse front from the point of view of the spatial frequency domain is given. 相似文献
14.
15.
S.L. Chin A. Talebpour J. Yang S. Petit V.P. Kandidov O.G. Kosareva M.P. Tamarov 《Applied physics. B, Lasers and optics》2002,74(1):67-76
Formation and wandering of filaments in air are studied both experimentally and numerically. Filament-center deflections are
collected from 1100 shots of 190-fs and 800-nm pulses in the plane perpendicular to the propagation direction. To calculate
the filament wandering in air we have developed a model of powerful femtosecond laser pulse filamentation in the Kolmogorov
atmospheric turbulence and employed the Monte Carlo method to model the propagation of several hundred laser pulses. Statistical
processing of experimental and numerical data shows that filament-center displacements in the transverse plane obey the Rayleigh-distribution
law. Parameters of the Rayleigh distribution obtained for numerical and experimental data are close to each other.
Received: 23 May 2001 / Revised version: 26 September 2001 / Published online: 29 November 2001 相似文献
16.
A. A. Ionin S. I. Kudryashov S. V. Makarov L. V. Seleznev D. V. Sinitsyn 《JETP Letters》2009,90(6):423-427
The propagation of focused femtosecond laser pulses with supercritical peak powers in air has been investigated by the methods
of optical visualization, profilometry, and calorimetry. Laser pulses with supercritical powers create a bundle of submillimeter
filaments with a diameter of about 5 μm ahead of the lens focus; the maximum number of filaments in the beam cross section
and their length increase linearly and sublinearly, respectively, with the radiation peak power. The optical visualization
and calorimetry indicate that the plasma channels of filaments are optical contrast (a plasma density of 1018–1019 cm−3), ensuring the refraction of laser radiation incident on them. 相似文献
17.
Multiple filamentation has been observed when focusing a femtosecond laser pulse into a methanol solution with an axicon. It is found that multiple long filaments are located on the central spot and ring structures of the quasi-Bessel beam created by the axicon. Since the quasi-Bessel profile is determined by the axicon properties, the axicon has been suggested as a simple optics to control multiple filaments. 相似文献
18.
G. Méjean J. Kasparian J. Yu S. Frey E. Salmon R. Ackermann J.P. Wolf L. Bergé S. Skupin 《Applied physics. B, Lasers and optics》2006,82(3):341-345
We report new experimental and numerical results on supercontinuum generation at ultraviolet/visible wavelengths produced
by the propagation of infrared femtosecond laser pulses in air. Spectral broadening is shown to similarly affect single filaments
over laboratory distance scales, as well as broad beams over long-range propagation distances. Numerical simulations display
evidence of the crucial role of third harmonic generation in the build-up of UV–visible wavelengths, by comparison with current
single-envelope models including chromatic dispersion and self-steepening.
PACS 52.38.Hb; 42.65.Tg; 42.65.Jx; 42.68.Ay 相似文献
19.
G. Méchain G. Méjean R. Ackermann P. Rohwetter Y.-B. André J. Kasparian B. Prade K. Stelmaszczyk J. Yu E. Salmon W. Winn L. A. Schlie A. Mysyrowicz R. Sauerbrey L. W?ste J.-P. Wolf 《Applied physics. B, Lasers and optics》2005,80(7):785-789
The propagation of femtosecond terawatt laser pulses at reduced pressure (0.7 atm) is investigated experimentally. In such
conditions, the non-linear refractive index n
2 is reduced by 30%, resulting in a slightly farther filamentation onset and a reduction of the filament number. However, the
filamentation process, especially the filament length, is not qualitatively affected. We also show that drizzle does not prevent
the filaments from forming and propagating. 相似文献
20.
A. Ródenas G. A. Torchia G. Lifante E. Cantelar J. Lamela F. Jaque L. Roso D. Jaque 《Applied physics. B, Lasers and optics》2009,95(1):85-96
The effect that femtosecond laser filamentation has on the refractive index of Nd:YAG ceramics, and which leads to the formation
of waveguide lasers, has been studied by micro-spectroscopy imaging, beam propagation experiments and calculations. From the
analysis of the Nd3+ luminescence and Raman images, two main types of laser induced modifications have been found to contribute to the refractive-index
change: (i) a lattice defect contribution localized along the self-focusing volume of the laser pulses, in which lattice damage
causes a refractive-index decrease, and (ii) a lattice strain-field contribution around and inside the filaments, in which
the pressure-driven variation of the inter-atomic distances causes refractive-index variations. Scanning near-field optical-transmission
and end-coupling experiments, in combination with beam propagation calculations, have been used to quantitatively determine
the corresponding contribution of each effect to the refractive-index field of double-filament waveguides. Results indicate
that the strain-field induced refractive-index increment is the main mechanism leading to waveguiding, whereas the damage-induced
refractive-index reduction at filaments leads to a stronger mode confinement. 相似文献