Hae June Lee

Propagation dynamics of optical vortices with anisotropic phase profiles

Propagation dynamics of optical vortices with anisotropic phase profiles, where the slope of the helical wave front is not uniform in the azimuthal direction, is studied in the linear and nonlinear regimes. Numerical results show that the rotation rate of optical vortices is proportional to the anisotropy and is in good agreement with the analytical approach.

Generation of high-energy electrons by a femtosecond terawatt laser propagating through a sharp downward density transition

We demonstrate by computer simulations the generation of high-energy electrons by using a femtosecond terawatt laser pulse propagating in a plasma with a sharp downward density transition. In the two-dimensional simulation, a 20-TW laser pulse with a pulse duration of 60 fs and a wavelength of 800 nm propagates through a plasma with a sharp density transition consisting of n0I=5×1018 cm−3 and n0II=0.75n0I. The simulation result demonstrates that a significant amount of electrons can be self-trapped and accelerated to an energy of 117 MeV over a distance of 0.62 mm by the ultrastrong nonlinear laser wake field. In addition, it has been found that the trapping dynamics is much different from the electron-beam-driven dynamics and that the energy spread of the trapped electrons can be reduced significantly by use of the density tapering method.

Characteristics of pulse compression in laser pulse amplification by stimulated Raman backscattering

The characteristics of pulse compression during the laser pulse amplification using two counter-propagating laser pulses have been investigated using a one-dimensional fluid model of stimulated Raman backscattering. The front and the rear pulse widths of the amplified laser pulse are examined in terms of the initial pump and seed amplitude, and the ratio of the electron plasma frequency to the laser frequency. The pulse widths have a common scaling behaviour in time over the considered parameter regime. The scaling exponents of the pulse widths during broadening and compression are all the same as 1.0. The pulse compression scaling shows a reciprocal behaviour to the peak energy growth.

Electron Injection by Evolution of Self-Modulated Laser Wakefields

Self-injection mechanisms in the self-modulated laser wakefield acceleration (SM-LWFA) are investigated. Two-dimensional (2D) particle-in-cell (PIC) simulations show that a significant amount of plasma electrons can be self-injected into the acceleration phase of a laser wakefield by a dynamic increase in the wake wavelength in the longitudinal direction. In this process, it is found that the wake wavelength increases due to the relativistic effect and this leads to a large amount of electron injection into the wakefields. In this paper, the injection phenomena are studied with 2D simulations and a brief explanation of the new self-injection mechanism is presented.