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Q: Fachverband Quantenoptik und Photonik

Q 63: Ultrakurze Laserpulse: Erzeugung und Anwendungen 2

Q 63.8: Talk

Friday, March 18, 2011, 12:15–12:30, SCH A215

Strong-field above-threshold photoemission from sharp metal tips — •Michael Krüger, Markus Schenk, and Peter Hommelhoff — Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, 85748 Garching bei München

We focus low-power few-cycle laser oscillator pulses on sharp tungsten tips and measure the energy of the emitted electrons. We observe above-threshold photoemission with a photon order of up to nine. At intensities exceeding 10¹¹ W/cm² we observe a suppression of the lowest-order peak as well as a shift of the spectral features towards lower energies [1]. This shift scales linearly with intensity with a slope of −1 eV/(10¹² W/cm²). We conclude that these phenomena owe to an AC Stark shift of the continuum states and thus are strong-field effects. A comparison of the measured shift with the shift expected from laser and focal spot parameters reveals that the laser electric field at the tip’s apex is enhanced by a factor of about 4. This enhancement enables us to enter the strong-field regime with low-power oscillator pulses only. Furthermore, we observe a plateau and a cut-off in the high-energy part of the spectra. This is an evidence that electrons recollide with the tip, implying that high-harmonic radiation can be expected to be generated at the tip. Also coherent control of photoemission should be feasible since strong carrier-envelope phase effects have been observed with this system [2].

[1] M. Schenk, M. Krüger, P. Hommelhoff, accepted for publication in Physical Review Letters (2010)

[2] see contribution of M. Schenk et al. at this conference