Geneva University
École de physique - Département de physique nucléaire et corspusculaire
24, quai Ernest-Ansermet
1211 GENÈVE 4
Tél: (022) 379 62 73 - Fax: (022) 379 69 92
Monday 2 November 2009
Colloquium
at 17:00 – Stückelberg Auditorium
Laser induced electron tunnel ionization : instantaneous or invalid concept?
Prof. Ursula Keller / Physics Department, ETH Zurich
It is typically assumed that electrons can escape from atoms through tunneling when exposed to strong laser fields, but the timing of the process has been controversial, and far too rapid to probe in detail. We have used attosecond angular streaking [1] to place an upper limit of 34 attoseconds and an intensity-averaged upper limit of 12 attoseconds on the tunneling delay time in strong field ionization of a helium atom in the non-adiabatic tunneling regime [2]. This is the fastest process that has ever been measured. To achieve this we exploit the exact timing of a close to circular polarized intense laser field in the two-cycle regime. Our experimental results give a strong indication that there is no real tunneling delay time, which is also confirmed with numerical simulations using the time-dependent Schrödinger equation. We hope that our results will shed some light on the ongoing theoretical discussion and stimulate additional discussions on strong field ionization and tunneling time. Tunneling theories are the standard approach to intense-field ionization and have successfully described high harmonic generation (HHG), quantum path interference in QPI and laser-induced electron tunneling and diffraction. On the other hand, as suggested by Reiss, tunneling may not be the appropriate picture to describe strong field ionization. In a velocity gauge treatment, no tunneling would be involved in the ionization process.
A drink with the speaker will be offered at the end of the colloquium.
Organizer: Prof. Markus Büttiker