CAVITY ELECTRODYNAMICS IN POLARITON SPECTRA OF THIN-FILMS

Optical properties of excitations in a ''vacuum or dielectric-dielectr ic or semiconductor films-metal substrate'' structure was investigated both experimentally, by methods of far-infrared spectroscopy, and the oretically, within the framework of macroscopic optics of crystals. It is shown that the optical properties of such structures are determine d by mixed polaritons of the structure and by size quantization of the electromagnetic field in these polaritons by the boundaries of the st ructure. The electromagnetic held of the states is determined by all d ipole-active excitations of each substance of the structure and depend s on the particular geometry of the experiment. A good agreement betwe en the measured and calculated frequencies, width, and shapes of the b ands of the mixed radiative polaritons of the structures in a wide ran ge of ''metal-semiconductor film-gap-ATR prism'' structure parameters (film and gap thicknesses, reflection and emission angles, and dielect ric constants of the structure) shows that these mixed polaritons are well-defined eigenstates of the electromagnetic field in real structur es. An analogy is drawn between the cavity modes in a microcavity and mixed polaritons of the sandwichlike structures. Parametric excitation of polaritons of a cavity by the use of femtosecond laser pulses is d iscussed.