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The interaction of free electrons with intense laser beams in vacuum is studied using a 3D test particle simulation model that solves the relativistic Newton-Lorentz equations of motion in analytically specified laser fields. Recently, a group of solutions was found for very intense laser fields that show interesting and unusual characteristics. In particular, it was found that an electron can be captured within the high-intensity laser region, rather than expelled from it, and the captured electron can be accelerated to GeV energies with acceleration gradients on the order of tens of GeV/cm. This phenomenon is termed the capture and acceleration scenario (CAS) and is studied in detail in this paper. The maximum net energy exchange by the CAS mechanism is found to be approximately proportional to a 2_o, in the regime where a_o > 100, where a_o = eE_o/m_ewc is a dimensionless parameter specifying the magnitude of the laser field. The accelerated GeV electron bunch is a macro-pulse, with duration equal or less than that of the laser pulse, which is composed of many micro-pulses that are periodic at the laser frequency. The energy spectrum of the CAS electron bunch is presented. The dependence of the energy exchange in the CAS on various parameters, e.g., a 2_o (laser intensity), w_o (laser radius at focus), tao (laser pulse duration), b_o (the impact parameter), and theta_i (the injection angle with respect to the laser propagation direction), are explored in detail. A comparison with diverse theoretical models is also presented, including a classical model based on phase velocities and a quantum model based on nonlinear Compton scattering.

The characteristics of electron scattering by intense pulsed laser beams and to determine the dependence of the net energy exchange on various parameters is studied. The interaction of free electrons with intense laser beams in vacuum is studied by using a three-dimensional test particle simulation model.

We demonstrate a frequency-tuning scheme that uses laser pulse duration to control the ultrafast-discharge current timescale. We also propose a simple physical model to explain the generation of terahertz radiation by laser propagation in an ultrafast-discharge.

We have demonstrated frequency upshift in the terahertz region by flash ionization. The magnitude of upshift frequency is tuned by the laser intensity. A proof of principle experiment has been performed with a plasma creation time scale much shorter than the period of the electromagnetic wave and a plasma length longer than its wavelength. Frequency upshifted from 0.35 to 3.5 THz by irradiating a ZnSe crystal with a ultra-short laser pulse has been observed.

We have reported the argon plasma waveguide produced in an alumina (Al2O3) capillary discharge and used to guide ultrashort laser pulses at intensities of the order of 1016 W/cm2. A one-dimensional magnetohydrodynamic (MHD) code was used to evaluate the average degree of ionization of Ar in the preformed plasma channel. The spectrum of the propagated laser pulse in the Ar plasma waveguide was not modified and was well reproduced by a particle-in-cell (PIC) simulation under initial ion charge state of Ar3+ in the preformed plasma waveguide. The optimum timing for the laser pulse injection was around 150 ns after initiation of a discharge with a peak current of 200 A.

The interaction of free electrons with intense laser beams in vacuum is studied using a three-dimensional test particle simulation model that solves the relativistic Newton-Lorentz equations of motion in analytically specified laser fields. Recently, a group of solutions was found for very intense laser fields that show interesting and unusual characteristics. In particular, it was found that an electron can be captured within the high-intensity laser region, rather than expelled from it, and the captured electron can be accelerated to GeV energies with acceleration gradients on the order of tens of GeV/cm. This phenomenon is termed the capture and acceleration scenario (CAS) and is studied in detail in this article. The accelerated GeV electron bunch is a macropulse, with duration equal to or less than that of the laser pulse, which is composed of many micropulses that are periodic at the laser frequency. The energy spectrum of the CAS electron bunch is presented. The dependence of the energy exchange in the CAS on various parameters, e.g., α[sub 0] (laser intensity), w[sub 0] (laser radius at focus), τ (laser pulse duration), b[sub 0] (the impact parameter), and θ [sub i] (the injection angle with respect to the laser propagation direction), are explored in detail. A comparison with diverse theoretical models is also presented, including a classical model based on phase velocities and a quantum model based on nonlinear Compton scattering. [ABSTRACT FROM AUTHOR]