High-efficiency generation of attosecond pulses during atomic ionization from excited electronic states

¹ Institute of Applied Physics, Russian Academy of Sciences 46 Ulyanov Str., Nizhny Novgorod 603950, Russia
² Physikalisches Institut, Universität Würzburg - Am Hubland 97074 Wurzbürg, Germany

Corresponding author: gerber@physik.uni-wuerzburg.de

Received: 26 November 2004
Accepted: 24 January 2005

Abstract

We show that the efficiency of single attosecond pulse generation during atomic ionization by an intense few-optical-cycle laser pulse can be enhanced dramatically when pre-excited electronic states are used. This is due to the slowed-down spreading of the laser-driven free-electron wave packet. We develop an analytical approach to the treatment of the attosecond burst production due to the electron recollision with a parent ion, assuming that the atom is fully ionized during one optical cycle. Our analytical and numerical simulations show that, when a hydrogen atom is ionized from the -state by an ultrashort pulse of a Ti:sapphire (800) laser, the energy of the generated attosecond pulse is several tens of times higher, its duration is much shorter, and the spectral intensity of radiation in the VUV and soft–X-ray range is several orders of magnitude superior to that in the case of ionization from the ground state. We determine the excited states preferable for experiments using the fundamental or the second harmonic of a Ti:sapphire laser.