Attosecond angular streaking: an ideal technique to measure an electron tunneling time?

Abstract

We used attosecond angular streaking to measure attosecond ionization dynamics in the non-adiabatic tunneling regime of helium using slightly elliptically polarized 5.9 fs pulses with a peak intensity ranging from 2.3 to 3.5 x 1014 W/cm2 (corresponding to a Keldysh parameter variation of 1.45 to 1.17). With our technique we could demonstrate intensityindependent “instantaneous” ionization with an accuracy of 50 as. Numerical simulations based on the time-dependent Schrödinger equation confirm such ionization behavior with no distinct electron wave packets. This implies that we would not expect a tunneling time or multi-photon ionization delay in the ionization dynamics.