• S Guha

      Articles written in Pramana – Journal of Physics

    • Parametric excitation of hybrid mode in magnetised piezoelectric semiconductors

      S Ghosh P K Sen S Guha

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      Using the hydrodynamic model of homogeneous plasma, the parametric decay of a laser beam into an acoustic wave and another electromagnetic wave has been studied in heavily dopedn-type piezoelectric semiconductors in the presence of a transverse magnetostatic field. This decay process results in the parametric excitation of the hybrid mode. The threshold electric field necessary for the onset of instability equals to zero. The magnetostatic field couples the acoustic and the electromagnetic waves and in its absence the instability disappears. The growth rate increases with the square of the magnetic field.

    • Effect of transverse static magnetic field on stimulated brillouin scattering of electromagnetic wave

      S Guha N Apte

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      Stimulated Brillouin scattering of a plane polarised electromagnetic wave propagating perpendicular to a static magnetic field has been investigated analytically in ann-type piezoelectric semiconductor-plasma. Using coupled mode theory the dispersion relation is obtained and the threshold value of the amplitude of electromagnetic wave for the onset of instability is studied for both the forward and back-scattered modes. The role of the magnetostatic field on the threshold conditions for the unstable mode has been discussed.

    • Stimulated raman scattering from plasma modes in magnetoactive semiconductors

      S Guha N Apte

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      Stimulated scattering off electron plasma mode is investigated analytically for the case when the pump wave is an intense circularly polarised electromagnetic wave propagating parallel to a homogeneous dc magnetic field in an isotropic semiconductor-plasma. The threshold electric field of the pump necessary for the stimulated Raman scattering and the growth rate of the parametrically unstable mode have been obtained for two cases (i)B0=0 and (ii) B0 ≠ 0. It is seen that the magnetic field does not significantly affect the threshold electric field as well as the growth rate provided the cyclotron frequency is small compared to the frequency of the pump wave. The threshold conditions are also found to be insensitive to the electron thermal velocity.

    • The dielectric constant of the binary liquid systemn. heptane + methanol near its critical temperature

      Y Jayalaxmi S Guha V C Vani E S R Gopal

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      The electrical capacitance of the binary liquid mixturen. heptane + methanol at its critical composition is studied in both one-phase and two-phase regions. The two-phase capacitance data are used with the known functional forms for the order parameter and the diameter to obtainTc andcc with greater precision. This helps in reducing the number of unknown parameters in the functional form for the one-phase capacitance. The data show consistency with an alpha (α) exponent for dc/dt in the one phase region.

    • Stimulated Brillouin scattering of an electromagnetic wave by an acoustic-like mode in multi-ion species plasmas

      S Guha Ruby Sarkar

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      Using an hydrodynamical model, analytical investigation of the stimulated Brillouin scattering of an electromagnetic wave by an acoustic-like mode has been done in a multi-ion species plasma. The acoustic-like mode is a new mode which propagates in a multi-ion plasma only. The non-linear dispersion relation and the growth rate of the excited modes are derived. The non-linearity arises through the motion of ions which is introduced through ponderomotive force. It is found that the growth rate can be controlled by several parameters like charge number, mass, density and temperature of the ions.

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