Special Presentation: Paul Berman

    Wednesday, December 10, 2014 - 2:00pm
    Franken Conference Room (Meinel 821)

    “Dipole Emission Above a Metallic or Dielectric Half Space”


    In this informal seminar, Berman will review the relevant physical mechanisms that determine how optical radiation penetrates into and propagates in metallic and dielectric media. To introduce the subject, he will recall Poynting’s theorem and examine its range of validity in media described by a complex permittivity. He will then consider dipole emission above a metallic or dielectric half space when the dipole is oriented perpendicular to the surface, a problem originally solved by Sommerfeld in the context of radio waves. Although there are numerous books and articles written about this problem, Berman did not find many discussions of the power flow in the metal or dielectric. In calculating the power flow, he found some surprises (at least they were surprises to him). In the case of a metallic half space, surface plasmon effects give rise to radial inward propagating waves. Even though the net power flow into the interface is positive, energy flows out of the metal at small radii (measured relative to the axis of the dipole); moreover, oscillations occur in the differential power entering the surface as a function of radius. In the case of a dielectric half space, new phenomena appear that are reminiscent of the Goos-Hanchen effect. The physical interpretation of the surface plasmon resonance frequency, as well as its relation to image charges, remains somewhat of a mystery to the speaker; perhaps attendees can shed some light on these matters.