Hannover 2010 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
Q: Fachverband Quantenoptik und Photonik
Q 21: Poster I
Q 21.86: Poster
Dienstag, 9. März 2010, 16:00–19:00, Lichthof
Processes of different nature in femtosecond-laser-induced electron emission from ultrasharp metal tips — •Michael Krüger, Markus Schenk, Johannes Hoffrogge, Hanno Kaupp, and Peter Hommelhoff — Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, 85748 Garching
We investigate electron emission from sharp tungsten tips induced by few-cycle femtosecond laser pulses. This unique combination of tip and laser pulse should provide high temporal and spatial coherence of the photo-emitted electrons. We report on emission processes triggered by 6fs Ti:sa laser pulses. A retarding field electron spectrometer enables identification of these processes. Typically we observe 10−4 to 10+3 electrons per pulse depending on the experimental parameters. At low laser intensities (<1012 W/cm2), multiphoton absorption and subsequent over-barrier emission occur (3-photon process). We can tune the effective workfunction by applying a static electric field to the tip, and thus are able to decrease the number of photons necessary to overcome the potential barrier (2-photon process). At high DC electric fields, additionally tunneling of photo-excited electrons out of the tip is observed (photo-field emission, 1-photon process). At high laser intensities on the order of 1012 W/cm2, electrons with energies corresponding to absorption of up to 7 photons are found (above-threshold photoemission). The nonlinearity of the processes can be determined by interferometric autocorrelation traces using the tip as nonlinear element. We model the observed energy distributions and have evidence that emission takes place via surface states for a certain parameter range.