Browsing by Author "Msoffe, Ngoda Nangohe"

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    Exciton polaritons in spatially dispersive medium
    (University of Dar es Salaam, 1981) Msoffe, Ngoda Nangohe
    Absorption of photons by electrons in the valence band of a semiconductor excites the electrons to the conduction band. The coupling of such electrons to their holes in the valence band creates a quasiparticle called and exciton. The propagating excitons in the crystal couple with the optical phonons of the lattice which form exciton polaritons when they couple with photons. In this thesis some optical properties of ecciton polaritons in a spatially dispersive (SD) medium are investigated on a theoretical basis. Some of the experimental studies are also reviewed. In all cases parameters for the 1S ex itons of Lead Iodide (PbI2) are used for illistration. In chapter 1 Euler-langrangian equation of motion and the Maxwells equations are used to derive the dispersion relation for exciton polaritons. Due to the existence of additional light waves (ALW) resulting from SD effects, additional boundary conditions (a.b.c. ) are needed in addition to Maxwell’s boundary conditions. In chapter 2 the study of Reflection and Transmission spectra is considered for the s- and p- waves configurations. The effect of mass, damping, angle of incidence and different additional boundary conditions are considered. In chapter 3 absorption by exciton Polaritons under normal and oblique incidence is investigated. It is shown that the usual definition for the optical absorption when there is no spatial dispersion cannot be extended to exciton Polarotpms in a spatially dispersive medium due to the ALW. In chapter 4 Methods of experimental studies on the properties of exciton polaritons are reviewed. A theoretical review of Brillouin scattering is also considered. In chapter 5 a detailed discussion of results of our investigation is done and some suggestions for further studies are attempted.