Browsing by Author "Yirgashewa, Tewodros"

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    Coherently Driven Three-Level Laser with Parametric Amplifier
    (Addis Ababa University, 2010-04) Yirgashewa, Tewodros; Kassahun, Fesseha (PhD)
    The squeezing and statistical properties of the light produced by a coherently driven degenerate as well as nondegenerate three-level laser with a parametric amplifier is studied applying c-number Langevin equations. Employing the solutions of these equations, we have determined the quadrature variance for the cavity and output modes, the squeezing spectrum for the output mode(s), the photon statistics of the cavity mode(s), and the photon number and count statistics of the output mode(s). It so turns out that the parametric amplifier increases the squeezing and the mean photon number significantly. Furthermore, it so happens that the coupling of the top and bottom levels enhances the degree of squeezing particularly when there are nearly equal number of atoms initially in the top and bottom levels. It is also found that one effect of the coupling of the top and bottom levels is to decrease the mean and the normally-ordered variance of the photon number. In addition, our calculation shows that the mean photon number of mode a is greater than that of mode b
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    Parametric Oscillation with Two-Mode Squeezed Vacuum and Coherent Light
    (Addis Ababa University, 2006-06) Yirgashewa, Tewodros; Kassahun, Fesseha (PhD)
    We obtain stochastic di®erential equations for the nondegenerate parametric oscillator with the cavity modes driven by coherent light and coupled to a two-mode squeezed vacuum reservoir. With the aid of these equations, we calculate the quadrature variance and the squeezing spectrum. It is found that the two-mode squeezed vacuum increases the degree of squeezing. It is also found that for ! = 0 the noise in the plus quadrature is completely suppressed. However, the two-mode driving light has no e®ect on the squeezing properties of the cavity modes. On the other hand, using the solutions of the stochastic di®erential equations, we calculate the mean and the variance of the photon number. It turns out that the two-mode driving light and the two-mode squeezed vacuum increase the mean and the variance of the photon number. Furthermore, employing the same solutions, we also obtain the antinormally ordered characteristic function de¯ned in the Heisenberg picture. With the help of the resulting characteristic function, we determine the Q function which is then used to calculate the photon number distribution. Moreover, we calculate the mean, the variance, the photon number distribution for the number of photon pairs, in the absence of the two-mode driving light