Dresden 2009 – scientific programme

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O: Fachverband Oberflächenphysik

O 46: Time-resolved spectroscopies I

O 46.7: Talk

Thursday, March 26, 2009, 12:00–12:15, SCH A315

Two-photon photoemission spectroscopy of image potential states on Ag(001): Momentum-dependent lifetimes and quantum beats — •Mario Kiel, Klaus Duncker, and Wolf Widdra — Martin-Luther Universität Halle-Wittenberg, Halle, Germany

Using a novel all-fiber based oscillator/amplifier system operating at a repetition rate of 1.5 MHz which pumps two noncollinear optical parametric amplifiers with tunable pulses (<30 fs) in the range of 500-950 nm, the n=1, 2 and 3 image potential states on Ag(001) have been investigated by time and momentum-resolved two-color two-photon photoemission spectroscopy (2PPE). Lifetimes of 55, 165 and 380 fs at k_||=0 have been determined for these states, respectively, similar to previous work [1]. The lifetime of the n=1 state reveals a quadratic momentum-dependence of the decay rate. This leads to a shortening to 26 fs at k_||=0.4 A⁻¹ which can be described by a linear 34 meV/eV decay rate increase with excess kinetic energy which is comparable to results on Cu(001) [2]. It clarifies the controversy regarding the existence of additional decay channels on Ag(001) vs. Cu(001) derived from intrinsic linewidth measurements [3].

Quantum beat spectroscopy is used to determine the energy difference between the n=3 and 4 states to 35 meV based on the 2PPE signal oscillation with a periodicity of 118 fs.

[1] I. L. Shumay, et al.; PRB 58 (1998), 13974

[2] W. Berthold, et al.; PRL 88 (2002), 056805

[3] G. Ferrini, et al.; PRB 67 (2003), 235407