No abstract

There are two modes of surface plasma waves: 1) Non-radiative modes with phase velocities Cü/k smaller than the velocity of light c. They cannot decay into photons in general.2) Radiative modes with (o/k > c which couple directly with photons 1 .The following paper is concerned with the excitation of these modes by light and their decay into photons. It has been shown that the radiative mode on thin silver-and potassium-films can be excited by light and that the mode reradiates light almost into all directions with an intensity maximum at the plasma frequency cOp 2 . It had been further observed that the non-radiative modes radiate under certain conditions if they are excited by electrons (grazing incidence of electrons on . a rough surface 3 or at normal incidence on a grating 4 ).The mechanism of this emission is in these cases always the same: The "wave vector" of the roughness of the surface or its irregularity changes the plasmon wave vector k so that a) in the case of the radiative mode light emission is found in directions in addition to that of reflexion and transmission, b) in the case of the non-radiative mode its wave vector is reduced so that the condition /c0, the wave vector of the inhomogeneous wave is (co/c) • Vsq' sin 0O (fq = 2.16 for quartz) and thus can excite a non radiative mode on the boundary of the prism for j/fq sin 0O > 1 or 90° > @o > 43°. If one vaporises a silver film directly on the quartz surface the inhomogeneous light wave penetrates into the silver film and excites a non-radiative mode on the boundary silver/air. The excitation will be highest for those frequencies which fulfill the dispersion relation of these surface plasmons.The dispersion relations at the boundary of (bulk) silver/air and silver/quartz are 7 /c 2 = £ + 1 and k 2 = _E Eq £ + £q with e, £q the real parts of the dielectric constants of silver and quartz. These relations are little modified by the fact that the silver has a finite thickness. At a thickness of about 1000 Ä Ag the difference between the exact formula and the formulas given above is not important. Fig. 1 demonstrates the dispersion relations and shows that those surface oscillations on the silver-airboundary can be excited which lie between co/k = c and

No abstract

No abstract

No abstract