Browsing by Author "Tesfa, Sintayehu"

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    Interaction of Two-Level Atoms with a Squeezed Vacuum
    (Addis Ababa University, 1997-06) Tesfa, Sintayehu; Kassahun, Fesseha (PhD)
    The squeezing and the statistical properties as well as the spectrum of the radiation resulting from the interaction of two-level atoms with a sqneezed vacuum is analyzed. We have considered the case in which the two-level atoms, all initially in the upper level, are placed in a squeezed vacuum. We have also considered the case in which the atoms, initially with nearly equal number in each level, are confined in a cavity coupled to a squeezed vacuum. The quadrature fluctuations, the photon number distribution and the spectrum of the the radiation are calculated using the Q-function formalism. The Q-function is determined applying the method of evaluating the propagator developed by Fesseha [19,20]. The radiation is found out to be in a squeezed state for certain period of time in the first case and for all times in the second case. It is also shown that one effect of the squeezed vacuum is to increase the height of the spectrum of the radiation
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    A Nondegenerate Three-Level Cascade Laser Coupled to a Two-Mode Squeezed Vacuum Reservoir
    (Addis Ababa University, 2008-02) Tesfa, Sintayehu; Kassahun, Fesseha (PhD)
    Detailed analysis of the squeezing of the cavity as well as the output radiation and statistical properties of the cavity radiation of a nondegenerate three-level cascade laser, in which the top and bottom levels of the injected atoms are coupled by an external coherent radiation, and whose cavity is coupled to a two-mode squeezed vacuum reservoir is presented. The generated radiation exhibits a high degree of squeezing in the minus quadrature either for a weak or strong driving radiation. In general, the degree of squeezing and mean number of photon pairs increase with the linear gain coefficient and squeeze parameter. The driving radiation leads to squeezing of the cavity radiation even when ´ = 0 and ´ = 1. Moreover, it is found that there is no distinct difference between the probability for finding odd and even number of photon pairs in the cavity. In addition, the mean number of photons in mode a turns out to be greater than that in mode b