Abstract

We report on our recent experimental progress on impact ionization and excitation of neutral helium and Neon atoms confined in filamentary plasma gratings. The plasma gratings were preformed via nonlinear interaction of two non-collinearly overlapped ultraviolet femtosecond filaments [1-5]. Intense infrared fs laser pulses were incident into the grating through nonlinear Bragg diffraction [1], which induced a dramatic enhancement of the local electron density up to 2×10¹⁹ cm⁻³. Electrons liberated away from neutral atoms or molecules through tunneling ionization were then driven by intense infrared fs pulses to gain ponderomotive energies. Such ponderomotive electrons could either trigger efficient impact ionization in filamentary plasma gratings [1-5] or collide with nearby atoms or molecules into some highly-lying excited states. By injecting buffer argon atoms or nitrogen molecules to liberate high-density seed electrons through multi-photo-ionization, helium or neon atoms within the well-confined plasma gratings could be efficiently excited with a substantial fraction of neutral survivals in high-lying atomic excitation.

© 2012 Optical Society of America