Abstract
Evanescent fields of surface plasmon polaritons (SPP) above metal surfaces can reach 1-2 orders of magnitude higher, nearly atomic field strengths in comparison to the relatively weak exciting laser fields of a femtosecond Ti:sapphire laser oscillator. We used these high plasmonic fields to study the characteristic SPP phenomena of intense field optics experimentally. It was found that both the intensity and the angular distribution of SPP emitted light depend nonlinearly on the exciting laser intensity in the higher-intensity, non-perturbative range of the interactions. These results are supported by our theory. At these strong excitations, an additional, depolarized, diffuse spectrum also appeared which can be attributed either to the fluorescence of Au, or to the non-equlibrium Planck radiation, originating from the fast cooling of the conduction electron cloud of Au excited by the femtosecond laser pulse.
Highlights
Surface plasmon polaritons (SPPs) are subject to extensive studies due to their unique properties, opening novel ways of studying the physics of the interaction of light with surfaces and surface electrons in the intensity range extending from perturbative phenomena up to extreme nonlinear optics
Very recently high harmonic generation (HHG) light was generated on atoms using the enhancement effect of the evanescent field [2]
We have shown that Ud governs and accounts for all known linear surface plasmon polaritons (SPP) processes, as far as we restrict ourselves to its first approximation term, Ud(1), where we expand Ud according to the displacement of the oscillating electron of the metal
Summary
Surface plasmon polaritons (SPPs) are subject to extensive studies due to their unique properties, opening novel ways of studying the physics of the interaction of light with surfaces and surface electrons in the intensity range extending from perturbative phenomena up to extreme nonlinear optics. According to very recent theoretical predictions [2,3,4,5,6], a quite new theoretical and experimental way is opened in which (in addition to the traditional works done at low excitation intensities) new investigations of intense field processes can be performed The basis of this new possibility is the use of SPP-enhanced strong electromagnetic fields that can be produced even with a simple Ti:sapphire laser oscillator alone. Very recently HHG light was generated on atoms (which is the complementary process of the strong laser field induced electron emission, ATI) using the enhancement effect of the evanescent field [2]
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