Wei-Ping Zang

Vacuum electron acceleration driven by two crossed Airy beams

Using numerical simulation, we have studied in detail vacuum electron acceleration driven by two crossed Airy beams with identical characteristics except for opposite accelerating directions. An electron injected along the longitudinal central axis is only affected by the combined longitudinal electric field. In addition, a suitable crossed Airy beams scheme is more beneficial to the energy gain of an electron than the single Airy beam acceleration scheme [Opt. Lett. 35, 3258 (2010)]. Meanwhile, the cross angle, the injection energy of the electron, and the initial phase of the Airy beams play significant roles in the energy gain of the electron.

Analysis of optical trapping and propulsion of Rayleigh particles using Airy beam

The radiation forces and trajectories of Rayleigh dielectric particles induced by one-dimensional Airy beam were numerically analyzed. Results show that the Airy beam drags particles into the optical intensity peaks, and guides particles vertically along parabolic trajectories. Viscosity of surrounding medium significantly affects the trajectories. Random Brownian force affects the trajectories. Meanwhile, trapping potential depths and minimum trapping particle radii in different potential wells were also discussed. The trapping stability could be improved by increasing either the input peak intensity or the particle radius.

Study on Z-scan characteristics for a large nonlinear phase shift

Using the Gaussian decomposition (GD) method, we studied the characteristics of a Z scan for a thin nonlinear medium with a large nonlinear phase shift induced by a pulsed laser. It has been verified that the GD method is still valid for analyses of Z-scan measurements with a large nonlinear phase shift and is better than some others, i.e., Fresnel-Kirchhoff diffraction and the aberration-free approximation model. By comparing the peak-to-valley configuration of Z-scan curves for a large nonlinear phase shift induced by a pulsed laser with that by a cw laser, we found that some peak-to-valley features of Z-scan curves appear as the aperture size or the light intensity increases in the case of a large nonlinear phase shift. Meanwhile, we carried out the Z-scan experiments of pure CS2 by a picosecond pulsed laser to verify the theoretical calculations in the case of a large nonlinear phase shift. The experimental results agree well with the theoretical calculations.

Electron acceleration in vacuum induced by a tightly focused chirped laser pulse

Electron acceleration in vacuum induced by a tightly focused chirped laser pulse has been studied. For a fixed laser output power, the tightly focused chirped laser pulse can accelerate electrons to much higher energies. Focusing laser down to the order of wavelength requires inclusion of terms of third order at least in the diffraction angle e in the description of the associated field. Retained electron energy depends strongly on frequency chirp parameter and initial position of the electron. Besides, retained energy increases with laser intensity, pulse duration, and initial velocity of electron, and varies periodically with laser constant phase.

TWO MODIFIED Z-SCAN METHODS FOR DETERMINATION OF NONLINEAR-OPTICAL INDEX WITH ENHANCED SENSITIVITY

Abstract Two modified Z -scan methods, in which the far-field on-axis aperture in common Z -scan is replaced by an off-axis aperture and a circular board, are suggested for measurements of n 2 with enhanced sensitivity. The calculated results show that with the increase of the distance from the off-axis aperture to the axis or the diameter of the circular board, the peak-valley normalised transmittance difference of Z -scan will increase rapidly. Also the Z -scan characteristics with a nonlinear absorption are analyzed.

Nonlinear ellipse rotation modified Z-scan measurements of third-order nonlinear susceptibility tensor

We present a method that combines the Z-scan technique with nonlinear ellipse rotation (NER) to measure third-order nonlinear susceptibility components. The experimental details are demonstrated, and a comprehensive theoretical analysis is given. The validity of this method is verified by the measurements of the nonlinear susceptibility tensor of a well-characterized liquid, CS2.

Analysis of beam propagation in thick nonlinear media.

We present a theoretical analysis of beam propagation in thick nonlinear media by using the Gaussian decomposition method and considering a thick medium as a stack of thin media. Simple analytic solutions of Z-scan characteristics and optical limiting with thick nonlinear media are obtained. Comparisons of these results with those obtained by use of a distributed-lens model and Gaussian-Laguerre mode decomposition are made. Good agreement is obtained with a distributed-lens model.

Vacuum electron acceleration driven by a tightly focused radially polarized Gaussian beam.

Electron acceleration in vacuum driven by a tightly focused radially polarized Gaussian beam has been studied in detail. Weniger transformation method is used to eliminate the divergence of the radially polarized electromagnetic field derived from the Lax series approach. And, electron dynamics in an intense radially polarized Gaussian beam is analyzed by using the Weniger transformation field. The roles of the initial phase of the electromagnetic field and the injection angle, position and energy of electron in energy gain of electron have been studied in detail.

Simulation of Gaussian laser beams and electron dynamics by Weniger transformation method

For an electron accelerated by a tightly focused Gaussian laser beam, its dynamics are usually simulated through the field obtained by Lax approach [Phys. Rev. A 11, 1365 (1975)]. However, as Lax series field (LSF) is not always convergent, the obtained results are usually inaccurate and even illogical. Here we report that the divergence of LSF can be eliminated by using Weniger transformation, and the electron dynamics simulated by this new field are logical and accurate.

Nonlinear absorption and optical limiting properties of carbon disulfide in a short-wavelength region

Nonlinear absorption of carbon disulfide (CS2) was studied in the wavelength region of 420-530nm by using Z-scan method with nanosecond pulses. Large nonlinear absorption was found in the short-wavelength region (420-460nm). The optical limiting properties of CS2 were also studied, and results showed that CS2 has good optical limiting capability in the 420-460nm region. The mechanism of the nonlinear absorption was analyzed by the temporal profile of pulses going through CS2. The large nonlinear absorption is believed to arise from a combination of two-photon absorption and the excited-state absorption induced by two-photon absorption.