Fast mode surface plasmon damping on tunnel junction structures

Using a prism-air gap-sample (Otto) configuration we have optically excited surface plasmon polaritons at the Ag-air interface of passive Al-Al oxide-Ag tunnel junction structures at wavelength 632.8 nm. It is found that the internal damping of this excitation is more than a factor of 2 greater for samples with a very thin ( ~ 15 nm) Ag electrode than for samples with a thicker ( ~ 40 nm) Ag electrode. This observation is explained by the fact that the fields of the surface plasmon polariton penetrate more substantially into the lossy Al base electrode when the Ag top electrode is very thin.