Norbert Kroo

Decay Length of Surface Plasmons Determined with a Tunnelling Microscope

A tunnelling microscope is used to detect surface plasmons (SP) on a silver-vacuum interface excited by a He-Ne laser. The decay length of the SP is determined experimentally, and the detection mechanism of the SP in the tunnelling microscope is discussed.

On the origin of light emission by tunnel junctions

Abstract Light emission of AlAl2O3-Ag structures prepared on periodic gratings was studied. It is shown that most of the observed light originates from the Ag-vacuum surface plasmons scattered by the periodic grating and surface roughness. Surface plasmons are directly excited by tunneling electrons.

Quantum metal optics

Experimental and theoretical studies of the statistical properties of surface plasmon polaritons (SPOs) are described. Both classical and non-classical properties of surface plasmons are analysed. The temporal statistical behaviour at low excitation level, as measured by detecting the SPO emitted photon statistics as expressed by the correlation function and the temporal photon count distribution, show that the SPOs preserve the photon statistics of the laser. In the spatial distribution of the plasmon field as measured by an STM, squeezing, i.e. non-classical properties, were found. Independent simple model calculations confirmed the existence of both enhanced EM fields of surface plasmons and their squeezed character.

Internal photoeffect in periodically corrugated MOM structures

Abstract Internal photoeffect and tunnel emission measurements on Al-Ox-Ag and Al-Ox-Au diodes made on holographic gratings refer to the equivalence of elementary processes in electron and photon generation via the top metal-vacuum interface surface plasmons.

Observation of few-cycle, strong-field phenomena in surface plasmon fields

We present experimental evidence of the generation of few-cycle propagating surface plasmon polariton (SPP) wavepackets. Ultrashort plasmonic pulses were generated by few-cycle laser pulses of 5.5 fs to 6.5 fs duration on a thin silver film of 50 nm thickness coated on the face of a right-angle prism to enable Kretschmann-type SPP coupling. SPP pulses were characterized by an autocorrelation-type measurement based on fourth order, nonlinear electron photoemission induced by the SPP field. The evaluation of the measured ultrashort, fringe-resolved autocorrelation curve of the SPP wavepacket (Fig. 1a) resulted in a retrieved SPP pulse length of 6.5 fs, as evidenced by the reconstructed curve in Fig. 1b. This first demonstration of the generation of few-cycle propagating SPP wavepackets on a metal surface has important applications in ultrafast plasmonics.

Nonlinear photoelectron emission from metal surfaces induced by short laser pulses: the effects of field enhancement by surface plasmons

Nonlinear electron emission processes induced by surface plasmon oscillations have been studied both experimentally and theoretically. The measured above-threshold electron spectra extend up to high energies whose appearance cannot be explained solely by standard non-perturbative methods, which predict photon energy separated discrete energy line spectra with the known fast fall–plateau–cutoff envelope shape, even when taking the large field enhancement into account. The theoretical analysis of our data, based on the concept of plasmon-induced surface near-field effects, gives a reasonably good explanation and qualitative agreement in the whole intensity range.

Dispersion anomalies of surface plasma oscillations in mom tunnel structures

Abstract SPO dispersion relations measured in periodically corrugated AlAl2O3Ag structures show deviations from the theoretical expectations. The change of the slope and the shift of the dispersion curves can be explained if the surface roughness is taken into account but the appearance of a momentum gap at the intersection of two branches cannot yet be explained satisfactorily.

Spontaneous emission of radiation by metallic electrons in the presence of electromagnetic fields of surface plasmon oscillations

The spontaneous emission of metallic electrons embedded in a high-intensity enhanced surface plasmon field is considered analytically. The electrons are described by dressed quantum states which contain the interaction with the plasmon field non-perturbatively. Considerable deviations from the perturbative behaviour have been found in the intensity dependence of the emitted fundamental and the second harmonic signals, even at moderate incoming laser intensities. The theoretical predictions deduced from the formalism are in good qualitative agreement with the experimental results.

A high precision ATR study of surface plasmon mediated reflectance in noble metal films

Abstract An ATR reflectometer was constructed using a twin goniometer system and lock-in detection technique. The angular resolution was ±0.015°, determined by the beam divergence of the HeNe and YAG laser light sources, while the error in reflectivity was less than ±2%. The angular distribution of the ATR reflection and backward resonance light emission was measured in evaporated silver and gold films of 30–90 nm thickness with both wavelengths (0.6382 and 1.064 μm). Exact roughness spectrums were determined by a fitting procedure using the Kroger-Kretschmann formulae. A relatively sharp thickness dependence was found in the components of the dielectric constant at both wavelengths.

Surface plasmon dispersion relation of gold determined by MOM tunnel structures

Abstract The dispersion relation of surface plasma oscillations of the Au-vacuum interface was determined from the light emission of AlAl 2 O 3 Au tunnel diodes. The comparison of results with previous data obtained on Ag indicate that the mechanism of light generation is qualitatively the same for all MOM structures if the anode is one of the noble metals.