Abstract

The basic properties of atoms, molecules, and solids are governed by ultrafast electron dynamics. Attosecond pulses bear the promise to resolve these electronic dynamics on their natural time scale, the atomic unit of time, which is 24 attoseconds. The high frequency of the pulses, however, means that in most of the experiments performed so far the electrons that are excited by attosecond pulses are directly moved into the ionization continuum, where they rapidly disperse [1,2]. More interesting dynamics arise when electrons are excited into bound [3] or autoionizing states [4]. Here we present a method to determine the dynamics of a bound wave packet excited by an attosecond pulse, while – for the first time – keeping track of its spectral content with high precision. The key idea is that coincident with the creation of the bound wave packet, we also launch a broad continuum wave packet (Fig. 1). This free wave packet serves as a reference when, after a variable delay, the bound wave packet is ionized by a 7 fs infrared laser pulse, locked in phase with the bound wave packet. The interference fringes observed in the photoelectron spectrum enable precise determination of the bound electron wave packet. As in Ramsey spectroscopy, the spectral precision is here set not by the bandwidth of the excitation pulse, but by the delay between the pump and probe pulses as well as the experimental energy resolution of the photoelectron spectrometer used.

© 2009 IEEE