Microfilamentation of spiral density wave in an optical field ionization produced plasma

Chen-Kang Huang^1*, Chaojie Zhang³, Ken Marsh³, Chan Joshi³, Jyhpyng Wang^1,2

¹Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
²Department of Physics, National Central University, Zhongli, Taiwan
³Department of Electrical and Computer Engineering, University of California Los Angeles, Los Angeles, USA

* Presenter:Chen-Kang Huang, email:powercurt@gmail.com

The self-organization of a spiral electron density modulation in a plasma produced by optical-field ionization (OFI) of gaseous media is studied. Because of the field strength dependence of the OFI process, an ionized electron acquires a spatial-dependent drift velocity when the ionizing laser has a spatial-temporal intensity distribution. This results in an inhomogeneous initial plasma and the formation of complex coherent patterns depending on the laser parameters and the gas species. Later on, microfilamentation driven by kinetic instabilities starts growing on top of these spiral density wave structures due to the inhomogeneous velocity and current density distribution. In supporting three-dimensional particle-in-cell simulations that self-consistently include the ionization of the gas and the subsequent evolution of the plasma, we have verified that both the formation and microfilamentation of the spiral density wave structure occur within less than 100 fs after the plasma is produced. These findings provide new insights on the transient states of optical-field ionized plasmas right after their production.

Keywords: Laser plasma, Plasma instability, Optical-field ionization, Pattern formation