Browsing by Author "Alemu Yilak"

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    Light Waves in a Composite of Cylindrical Nanoinclusions in Passive and Active Host Matrices
    (Addis Ababa University, 2014-06) Alemu Yilak; Mal'nev Vadim (Professor)
    In this thesis work, we have studied the optical properties of a composite with metal coated di- electric cylindrical nanoinclusions / pure metal cylindrical nanoinclusions in passive and active dielectric host matrices. In order to compare results, we have also brie y discussed optical prop- erties of a composite with spherical nanoinclusions in passive and active dielectric host matrices. One of the optical properties of the composite we have investigated by this work is the lo- cal eld enhancement factor at the core of the inclusions. The obtained result shows that for a composite of metal covered dielectric inclusions in passive host matrix there are two maximum values of the local eld enhancement factor at two di erent resonant frequencies. For composite with dielectric covered metal inclusions only one peak of local eld enhancement factor deter- mined. We have also found that for a composite with pure metal cylindrical inclusion there is only one maxima of the local eld enhancement factor. In this work, the second main target of study interest was to determine the group velocity of narrow light wave packet that propagate in the overstated composites. We have determined that wave can travel with group velocity much slower than the speed of light in vacuum and faster than the speed of light in vacuum. Furthermore, we have found light waves that propa- gates with negative group velocity through the composite. In passive host matrix the light pulse seen absorbed within a very small distance when compared to the distance it travels in active host matrix. Hence the problem of absorption considerably reduced by using active host matrix