Control of laser light by a plasma immersed in a tunable strong magnetic field.

Xiaolong Zheng,Zhengming Sheng,Min Chen,Suming Weng,Hanghang Ma,Paul Mckenna,Yuanxiang Wang

doi:10.1364/oe.27.023529

Abstract

The interaction between laser light and an underdense plasma immersed in a spatio-temporally tunable magnetic field is studied analytically and numerically. The transversely nonuniform magnetic field can serve as a magnetic channel, which can act on laser propagation in a similar way to the density channel. The envelope equation for laser intensity evolution is derived, which contains the effects of magnetic channel and relativistic self-focusing. Due to the magnetic field applied, the critical laser power for relativistic self-focusing can be significantly reduced. Theory and particle-in-cell simulations show that a weakly relativistic laser pulse can propagate with a nearly constant peak intensity along the magnetic channel for a distance much longer than its Rayleigh length. By setting the magnetic field tunable in both space and time, the simulation further shows that the magnetized plasma can then act as a lens of varying focal length to control the movement of laser focal spot, decoupling the laser group velocity from the light speed c in vacuum.

Highlights

Compared to the low breakdown threshold of optical crystal devices, a plasma can tolerate much higher laser intensities (∼ 1017 W cm−2 or more) and is routinely used as an amplification medium in the Raman [1,2,3,4] or Brillouin [5,6,7,8] amplification regime to amplify seed laser pulses or as a plasma mirror [9] to increase the contrast of intense laser pulses
If this nonuniform magnetic field is time-varying, i.e. B = B(r, t), the magnetized plasma can act as a lens of varying focal length, which can manipulate the movement of focused laser peak in vacuum
A 2D PIC simulation is performed to show that the plasma under a time-varying nonuniform magnetic field can act as a lens of dynamic focal length to control the movement of the laser intensity peak in vacuum

Summary

Introduction

Compared to the low breakdown threshold (limited to 1012 W cm−2) of optical crystal devices, a plasma can tolerate much higher laser intensities (∼ 1017 W cm−2 or more) and is routinely used as an amplification medium in the Raman [1,2,3,4] or Brillouin [5,6,7,8] amplification regime to amplify seed laser pulses or as a plasma mirror [9] to increase the contrast of intense laser pulses. Plasma may be used for cross beam energy transfer [10], polarization control of light waves [11,12,13,14], information storage and retrieval [15], generation of relativistic single-cycle tunable infrared pulse [16], optical modulator [17], and apertures [18, 19]. A magnetic field with nonuniform transverse distribution can pave a magnetic channel in a uniform plasma, in which the ultrashort laser pulse can propagate with a nearly constant intensity for a distance many times longer than the Rayleigh length. It is further shown that a plasma slab immersed in a spatio-temporally tunable magnetic field can act as a lens of varying focal length to realize the dynamic focusing of laser beams in vacuum

Theoretical analysis

Simulation results and discussions

Conclusion