250 resultados para titled pulse front
em Chinese Academy of Sciences Institutional Repositories Grid Portal
Resumo:
Ultra-broadband optical parametric chirped-pulse amplification is analyzed based the compensation of phase-mismatch, which is achieved by matching of both group-velocity and pulse-front between signal and idler by the combination of the noncollinear-phase-match and pulse-front-tilt. The results show exactly matching of both group-velocity and pulse-front is the important criterion for constructing an UBOPCPA. Its general model is developed, in which the group velocities, noncollinear angles. spatial walk-off angles, linear angular spectral dispersion coefficients and pulse-front tilted angles are suitably linked to each other. Finally, specific numerical calculations and simulations are presented for beta-barium borate OPCPA with type-1 noncollinear angularly dispersed geometry. (C) 2005 Elsevier B.V. All rights reserved.
Resumo:
We propose a LBO-based ultra-broadband chirped pulse optical parametric amplifier employing pulse-front-matching to yield transform-limited sub-12-fs pulses. Measurement of the maximum possible gain bandwidth for the LBO-based OPCPA demonstrates more than 60nm gain bandwidth FWHM. For the generation of TL pulses by the use of this OPCPA, a suitable combination of OPCPA and PFM is first presented. The PFM pump geometry realizes tilt-free signal amplification, and permits this OPCPA to generate TL sub-12-fs pulses.
Resumo:
Optical parametric chirped-pulse amplification (OPCPA) supplies broadband gain for ultrashort pulses. A new theoretic explanation of OPCPA has been obtained by introducing the concept of tilted pulse front in this paper, and the distribution of broadband amplification has been twice expanded by introducing the technology of achromatic phase matching (APM). The prospect of APM in OPCPA has been discussed in detail. Finally, a design for the amplification of chirped pulses at 1600 nm has been firstly proposed and numerically simulated. (C) 2004 Elsevier B.V. All rights reserved.
Resumo:
In laser-target interaction, the effects of laser intensity on plasma oscillation at the front surface of targets have been investigated by one-dimensional particle in cell simulations. The periodical oscillations of the ion density and electrostatic field at the front surface of the targets are reported for the first time, which is considered as an intrinsic property of the target excited by the laser. The oscillation period depends only on initial plasma density and is irrelevant with laser intensity. Flattop structures with curves in ion phase space are found with a more intense laser pulse due to the larger amplitude variation of the electrostatic field. A simple but valid model is proposed to interpret the curves.
Resumo:
A preliminary experiment was carried out to validate the feasibility of the method of impact by a front-end-coated bullet to evaluate the interface adhesion between film and substrate. The theoretical description of the initiation, propagation and evolution of the stress pulse during impact was generalized and formulized. The effects of the crucial parameters on the interface stress were further investigated with FEM. The results found the promising prospect of the application of such a method and provided useful guidance for experimental design.
Resumo:
Particle-in-cell simulations are performed to study the acceleration of ions due to the interaction of a relativistic femtosecond laser pulse with a narrow thin target. The numerical results show that ions can be accelerated in a cascade by two electrostatic fields if the width of the target is smaller than the laser beam waist. The first field is formed in front of the target by the central part of the laser beam, which pushes the electron layer inward. The major part of the abaxial laser energy propagates along the edges to the rear side of the target and pulls out some hot electrons from the edges of the target, which form another electrostatic field at the rear side of the target. The ions from the front surface are accelerated stepwise by these two electrostatic fields to high energies at the rear side of the target. The simulations show that the largest ion energy gain for a narrow target is about four times higher than in the case of a wide target. (c) 2006 American Institute of Physics.
Resumo:
Acceleration of an initially moving electron by a copropagation ultra-short ultra-intense laser pulse in vacuum is studied. It is shown that when appropriate laser pulse parameters and focusing conditions are imposed, the acceleration of electron by ascending front of laser pulse can be much stronger compared to the deceleration by descending part. Consequently, the electron can obtain significantly high net energy gain. We also report the results of the new scheme that enables a second-step acceleration of electron using laser pulses of peak intensity in the range of 10(19)-10(20) W mu m(2)/cm(2). In the first step the electron acceleration from rest is limited to energies of a few MeV, while in the second step the electron acceleration can be considerably enhanced to about 100 MeV energy.
Resumo:
The steady state ion acceleration at the front of a cold solid target by a circularly polarized flat-top laser pulse is studied with one-dimensional particle-in-cell (PIC) simulation. A model that ions are reflected by a steady laser-driven piston is used by comparing with the electrostatic shock acceleration. A stable profile with a double-flat-top structure in phase space forms after ions enter the undisturbed region of the target with a constant velocity. (C) 2007 Elsevier B.V. All rights reserved.
Resumo:
A multiple-staged ion acceleration mechanism in the interaction of a circularly polarized laser pulse with a solid target is studied by one-dimensional particle-in-cell simulation. The ions are accelerated from rest to several MeV monoenergetically at the front surface of the target. After all the plasma ions are accelerated, the acceleration process is repeated on the resulting monoenergetic ions. Under suitable conditions multiple repetitions can be realized and a high-energy quasi-monoenergetic ion beam can be obtained.
Resumo:
The interaction of an ultraintense circularly polarized laser pulse and a solid target is studied by one-dimensional particle-in-cell simulations. Ions at the front of the target are reflected by a moving quasisteady electrostatic field and obtain a relativistic velocity. At a laser intensity of 10(22) W/cm(2), almost half of the laser energy is transferred to ions and GeV ions are obtained. Effects of laser polarization state and target thickness on the laser energy conversion are investigated. It is found that a circularly polarized laser pulse can accelerate ions more efficiently than a linearly polarized laser pulse at the same laser and target parameters. A monoenergetic ion bunch is obtained for the ultrathin target, which is accelerated as a single entity. (c) 2007 American Institute of Physics.
Resumo:
This report presents the experiments to study the characteristics of the picosecond ultra-wideband pulses coherent radiation. The testing involves bow-tie horn antennas for both the transninting and receiving antenna. Sixteen channels of electrical pulses with 290 ps duration and jitter < 30 ps have been used. The antenna arrays with various frames of 4 x 1, 4 x 2, 4 x 3, 4 x 4 are employed to radiate the pulses. The receiving antenna measures the electrical field in different distance front the transmitting antennas arrant The results show that if the pulses are in coherent condition, the peak power pulse of output by antennas array with N elements are N-2 of that of the single element antenna. (c) 2007 Wiley Periodicals, Inc.
Resumo:
Measurement while drilling (MWD) has become a popular survey technology to monitor directional data, drilling data, formation evaluation data and safety data in the world. And closed loop drilling shows promise in recent years. Obviously, the method of tr