title: Coherent terahertz echo of tunnel ionization in gases.
abstract: We study tunnel ionized electron wave packet dynamics during the initial transition from a gas to a plasma by detecting the terahertz radiation emitted in the process. Experimental and theoretical results show that much of the observed radiation is due to coherent buildup of bremsstrahlung released during the first electron-atom collision. Coherent control of the tunnel ionization process combined with ab initio modeling provides a real-time view of the initial stages of the formation of a laser-induced plasma and allows us to fully understand this important source of terahertz radiation.
authors.affiliation: Center for Terahertz Research, Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180, USA.
authors.forename: N
authors.initials: N
authors.lastname: Karpowicz
authors.forename: X-C
authors.initials: XC
authors.lastname: Zhang