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Aközbek N Iwasaki A Becker A Scalora M Chin SL Bowden CM 《Physical review letters》2002,89(14):143901
It is shown, both theoretically and experimentally, that during laser pulse filamentation in air an intense ultrashort third-harmonic pulse is generated forming a two-colored filament. The third-harmonic pulse maintains both its peak intensity and energy over distances much longer than the characteristic coherence length. We argue that this is due to a nonlinear phase-locking mechanism between the two pulses in the filament and is independent of the initial material wave-vector mismatch. A rich spatiotemporal propagation dynamics of the third-harmonic pulse is predicted. Potential applications of this phenomenon to other parametric processes are discussed. 相似文献
3.
We experimentally study the effect of the air gap on conversion efficiency and the spectrum of generated third-harmonic pulses in the dual-tripler broadband third-harmonic generation scheme. The experimental results are in good agreement with predictions that the 4-cm air gap is equivalent to a full cycle of phase mismatch among the three interacting pulses (i.e. the fundamental, second-harmonic and third-harmonic pulse). The experimental results also show that the spectrum of the third-harmonic pulse is sensitive to the air gap. We also point out that the air gap effect can be ignored when the dual-tripler system is located in 1000 Pa atmosphere. These results will guide the design of the broadband third-harmonic generation system in high power lasers. 相似文献
4.
A. V. Denisov A. G. Kuznetsov D. S. Kharenko S. I. Kablukov S. A. Babin 《Laser Physics》2011,21(2):277-282
The frequency doubling and tripling in a Q-switched all-fiber laser are studied. It is demonstrated that the main limitations
on the efficiency of the harmonic generation are related to the random polarization that is nonuniform with respect to axes,
the asymmetric pulse shape with a flat trailing edge, and the significant spectral broadening of the multimode radiation of
the fiber master oscillator in the fiber amplifier. The methods to increase the efficiency are proposed. For an IR pulse energy
of about 0.3 mJ, duration of about 40 ns, and repetition rate of 1 kHz, the second- and third-harmonic pulse energies are
greater than 60 and about 10 μJ, respectively. 相似文献
5.
Ultrabroadband continuum generated in air (down to 230 nm) using ultrashort and intense laser pulses
We present results on supercontinuum generation extended up to 230 nm in air during the propagation of a powerful femtosecond laser pulse. The broad supercontinuum generated in air is contributed by self-phase modulation and self-steepening of the fundamental laser pulse, the third-harmonic pulse and their interaction. In particular, the strong interaction between the fundamental and the third-harmonic pulses leads to broad and efficient continuum generation of the third-harmonic pulse itself. The spectrum of the third-harmonic generated in air extends over several tens of nm and overlaps with the shorter wavelength extent of the fundamental continuum. PACS 42.65.Ky; 42.65.Jx; 52.35.Mw 相似文献
6.
The resonant third-harmonic generation of a self-focusing laser in plasma with a density transition was investigated. Because of self-focusing of the fundamental laser pulse, a transverse intensity gradient was created, which generated a plasma wave at the fundamental wave frequency. Phase matching was satisfied by using a Wiggler magnetic field, which provided additional angular momentum to the third-harmonic photon to make the process resonant. An enhancement was observed in the resonant third-harmonic generation of an intense short-pulse laser in plasma embedded with a magnetic Wiggler with a density transition. A plasma density ramp played an important role in the self-focusing, enhancing the third-harmonic generation in plasma. We also examined the effect of the Wiggler magnetic field on the pulse slippage of the third-harmonic pulse in plasma. The pulse slippage was due to the group-velocity mismatch between the fundamental and third-harmonic pulses. 相似文献
7.
F. Théberge J. Filion N. Aközbek Y. Chen A. Becker S.L. Chin 《Applied physics. B, Lasers and optics》2007,87(2):207-210
Self-stabilization of the laser pulse parameters is demonstrated during the two-color filamentation of ultrashort and intense
laser pulses in gases. Experimental data and results of numerical simulations show, in good qualitative agreement, that the
root-mean-square values of the intensity fluctuations decrease below the initial value for the near-infrared pump pulse and
the perturbative limit for the third-harmonic pulse in the filament. It is found that the stabilization of the third-harmonic
intensity and energy are due to intensity clamping of the pump pulse and a constant ‘volume’ of the laser pulse during the
nonlinear propagation inside the filament.
PACS 42.65.Ky; 42.65.Jx; 52.35.Mw 相似文献
8.
N. Aközbek A. Becker M. Scalora S.L. Chin C.M. Bowden 《Applied physics. B, Lasers and optics》2003,77(2-3):177-183
The continuum generation by intense femtosecond IR laser pulses focused in air including the effect of third-harmonic generation is investigated. We have used a theoretical model that includes the full spatio-temporal dynamics of both the fundamental and the third-harmonic pulses. Results of our numerical calculations show that a two-color filamentation effect occurs, in which the third-harmonic conversion efficiency remains almost constant over the whole filament length. It is found that this effect is rather independent of the wavelength of the input beam and the focal geometry. During the filamentation process the third-harmonic pulse itself generates a broad continuum, which can even overlap with the continuum of the fundamental pulse for the longer pump wavelengths. In consequence, the continuum generation generated by intense IR laser pulses is further extended into the UV. PACS 42.65.Jx; 42.65.Ky; 52.35.Mw 相似文献
9.
A method for measuring resonances using a combination of third-harmonic generation and frequency-domain interferometry is described and demonstrated in an index-matched dielectric material. The phase of the third-harmonic spectrum of a pulse generated from a resonant NdAlO(3) thin film and a temporally displaced sapphire substrate pulse was measured by analyzing the spectral interference pattern. The appropriate combination of substrate and film signals was obtained by translating the sample through the laser focus while observing the third-harmonic intensity. 相似文献
10.
Spectral modulation of third-harmonic generation by molecular alignment and preformed plasma
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We demonstrate spectral modulation of third-harmonic generation from molecular alignment effects. The third harmonic spectrum is broadened or narrowed under different influences of cross-phase modulations originating from various molecular alignment revivals. Furthermore, the spectrum and spatial distribution of the generated third harmonic pulse change dramatically in the presence of a preformed plasma. Under the influence of a preformed plasma, a narrower third harmonic spectrum is observed, and the conical third-harmonic pulse increases while the axial part decreases. The investigation provides an effective method to modulate the spectral characteristic and spatial distribution of third-harmonic generation from intense femtosecond filament. 相似文献
11.
It is demonstrated numerically that the supercontinuum generation and third-harmonic generation that accompany optical filamentation in nonlinear dispersive bulk media can be described as first-order scattering processes akin to the first Born approximation. In particular, for an incident ultrashort pulse the angularly resolved spectrum of the transmitted pulse is shown to be accurately determined using first-order scattering of the incident field from the nonlinearly modified refractive index due to the optical filament. Thus, although an optical filament is a highly nonlinear object, the accompanying supercontinuum generation and third-harmonic generation are driven parametrically by the filament and have negligible back action upon it. 相似文献
12.
We demonstrate, for the first time to our knowledge, that efficient third-harmonic generation can be achieved with a cubic contribution much larger than the quadratic processes. An energy-conversion efficiency of 2.4% is achieved for cubic third-harmonic generation that is phase matched along the x axis of a KTiOPO(4) crystal by use of a picosecond fundamental laser emitting at 1618 nm. The associated cascading processes are only 10% of the pure cubic interaction, which is very suitable for study of the specific quantum optical correlations. Calculations of the third-harmonic generation conversion efficiency with respect to group-velocity dispersion and to the longitudinal Gaussian beam profile account well for our experimental results. 相似文献
13.
H. Xu W. Chu Y. Liu W. Liu H. Xiong Y. Fu J. Yao B. Zeng J. Ni S. L. Chin Y. Cheng Z. Xu 《Applied physics. B, Lasers and optics》2011,104(4):909-912
We experimentally demonstrate third-harmonic generation (THG) by intense femtosecond laser pulse at a central wavelength of ??800?nm superposed by its second harmonic in air. The third-harmonic signal shows a periodic modulation with a period of ??0.67?fs when the delay between fundamental and second-harmonic wave is continuously changed. The periodic modulation of THG can be attributed to the interference of third-harmonic signals generated from a direct THG channel (3??=??+??+??) and a four-wave mixing (FWM) channel (3??=2??+2?????). With high pump intensity, the fitting of the measured TH spectrum as a function of delay implies that the pump pulse undergoes a strong pulse splitting and self-phase modulation at the focus. 相似文献
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A novel scheme to achieve broadband cascaded third-harmonic generation by use of two-dimensional quasi-phase-matching gratings is proposed. Intrinsic group-velocity mismatch is compensated by the pulse front tilt in noncollinear interaction geometry. The presented scheme enables broadband third-harmonic generation in a single device of long interaction length, which reduces the operation intensity dramatically. 相似文献
16.
Sergii O. Iakushev Oleksiy V. Shulika Igor A. Sukhoivanov 《Optics Communications》2012,285(21-22):4493-4499
The passive nonlinear reshaping in normally dispersive optical fibers in the steady-state regime is studied numerically. It is found that normal dispersion and self-phase modulation are able to provide pulse reshaping towards a parabolic pulse profile at the distances exceeding the optical wave breaking length. However, as compared to the similariton formation in active fibers the resulted pulse shape in passive fibers is strongly depended on the initial pulse parameters and nonlinear and dispersive fiber properties as well. The influence of initial pulse shape, initial chirp, third-order dispersion and loss on the parabolic pulse formation is studied consistently, and estimation of practical conditions which are needed for parabolic pulses formation in a passive fiber is provided. 相似文献
17.
A. M. Basharov A. I. Maimistov S. O. Elyutin 《Journal of Experimental and Theoretical Physics》1999,88(1):16-23
The problem of the interaction of an ultrashort optical pulse and a thin film of resonant atoms under the conditions of two-photon
absorption, third-harmonic generation, and the inverse effect of the latter on the pump pulse via Raman scattering is studied.
The fact that the field acting on an atom differs from the macroscopic field in the film is also taken into consideration.
It is shown that the polarization of the film undergoes dynamic relaxation even in the absence of irreversible relaxation,
suppressing Rabi oscillations and establishing stationary values of the populations of the resonant energy levels and of the
polarization of the film at the pump and the third-harmonic frequencies.
Zh. éksp. Teor. Fiz. 115, 30–42 (January 1999) 相似文献
18.
Centini M Roppo V Fazio E Pettazzi F Sibilia C Haus JW Foreman JV Akozbek N Bloemer MJ Scalora M 《Physical review letters》2008,101(11):113905
We theoretically predict and experimentally demonstrate inhibition of linear absorption for phase and group velocity mismatched second- and third-harmonic generation in strongly absorbing materials, GaAs, in particular, at frequencies above the absorption edge. A 100-fs pump pulse tuned to 1300 nm generates 650 and 435 nm second- and third-harmonic pulses that propagate across a 450-microm-thick GaAs substrate without being absorbed. We attribute this to a phase-locking mechanism that causes the pump to trap the harmonics and to impress on them its dispersive properties. 相似文献
19.
The generation of lower (third) and higher harmonics of femtosecond laser radiation in plasmas produced by laser ablation
of different targets with a small atomic number Z (B, Be, Li) has been investigated. The high (10−3) efficiency of third-harmonic generation was observed in plasma produced on the boron surface. Efficient third-harmonic generation
was also observed in beryllium plasma using femtosecond pulses of Ti:sapphire laser radiation (λ = 790 nm) and its second
harmonic (395 nm). We could tune the higher harmonics generation spectrum by tuning the crystal converter when using 395-nm
radiation to be converted. It is shown that, in plasmas formed on targets with small Z, the conversion efficiency and limiting generated harmonic order depend on the delay between the ablation pulse and the pulse
to be converted. 相似文献
20.
Hongfu Li Zhong-Lian Xie Wenxiang Wang Yong Luo Pinzhong Du Xue Den Huajun Wang Sheng Yu Xinjian Niu Li Wang Shenggang Liu 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2003,31(2):264-271
A systematic theoretical and experimental study on a 35-GHz 45-kV third-harmonic gyrotron with a permanent magnet system is presented in this paper. A complex cavity with gradual transition and a diode magnetron injection gun (MIG) are employed in the gyrotron. A self-consistent field nonlinear theoretical investigation and numerical simulation for electron beam interaction with RF fields are given. The diode MIG is simulated numerically utilizing our code in detail. The permanent magnet system provided the maximum axial magnetic field of about 4.5 kG in the cavity region of the gyrotron. The Ka band third-harmonic complex cavity gyrotron with a permanent magnet system has been designed, constructed, and tested. A pulse output power of 147.3 kW was obtained at a beam voltage of 45 kV with beam current of 32.2 A, corresponding to an efficiency of 10.2%. 相似文献