S. Ghosh

Modulational Amplification of the Polaron Mode in a Magnetized Semiconductor

The present paper is concerned with the analytical study of the modulational amplification of the polaron mode in a magnetized semiconductor. Using the hydrodynamical approach and coupled mode theory we developed analytical expressions for the necessary threshold pump field, third-order susceptibility, and growth rate. Numerical estimations are made for n-InSb crystal at 77 K, irradiated with a 10.6 μm CO2 laser. In a limited range of the parameters (external electric field E0, carrier concentration n0, and cyclotron frequency ωc) a stable behavior of the growth rate and threshold for amplification of the polaron mode are observed. Beyond a certain range of parameters we obtain anomalous behaviour. Heavily doped medium is found to require a lower threshold field. An appropriate magnitude of the transverse magnetic field effectively enhances the growth rate (≈ 10^10 m^(-1)). Hence, the presence of an external magnetic field is favourable for the onset of modulational amplification of the polaron mode in the heavily doped regime.

Operational characteristics of doped InSb/CO2 plasma system: Effect of collective excitation

The effect of coupled vibration frequency via excitation of collective cyclotron modes and optical phonons on operational characteristics of doped InSb/CO2 plasma system is studied. Favourable conditions for utilizing this system as optical parametric amplifier under externally applied fields are explored. Within the applied framework a strong tunable electromagnetic Stokes wave may be achieved as signal wave at the expense of the pump wave. Polar optical scattering mechanism has been chosen to be dominant so that coherent polaron modes may be excited through ultra fast excitations. It will enable us to investigate the influence of collective excitation modes on the various optical properties of the medium. Numerical estimations are performed with a set of data appropriate for the said system at liquid nitrogen temperature. Results suggested that the achieved resonance conditions considerably diminish the threshold field required to incite the parametric interaction process. An important finding is that t...

Hybrid em wave - polar semiconductor interaction: A polaronic study

Present paper considers incidence of a most realistic hybrid pump wave on a weakly polar semiconductor having a very small coupling constant. Possibility of optical parametric interaction has been explored in the presence of an external transverse magnetic field. The effect of doping concentrations and transverse magnetostatic field on threshold characteristics of optical parametric interaction in polar semiconductor plasma has been studied, using hydrodynamic model of semiconductors, in the far infrared regime. Numerical estimations have been carried out by using data of weakly polar III-V GaAs semiconductor and influence of control parameters on electron-LO phonon interaction has been analyzed. A particular range of physical parameters is found to be suitable for minimum threshold. The choice of nonlinear medium and favorable range of operating parameters are crucial aspects in design and fabrication of parametric amplifiers and oscillators. The hybrid mode of the pump is found to be favorable for the onset of the said process and realization of a low cost amplifier.

Infra-red parametric generation: Phase mismatch condition

An analytical investigation is made for the Infrared parametric generation in doped semiconductor plasma under phase mismatch condition. Theoretical formulations are undertaken to determine induced polarization and threshold pump field for the onset of parametric generation in semiconductor plasma medium. The origin of this nonlinear interaction lies in the second order optical susceptibility arising due to the induced nonlinear current density in piezoelectric medium. Numerical estimations are made for n- type InSb at 77u2005K duly irradiated by a pulsed 10.6µm CO2 laser. It is very difficult to attain exact phase matching in experimental frame so we have considered a tolerable small phase mismatch in order to attain a new result. Its effect on the Infrared parametric generation in compound semiconductor is examined through induced polarization. Transmitted intensity is determined to have an idea about conversion efficiency of the said process. Phase mismatch tends to raise the required pump field to stimula...

Drift Modified Longitudinal Electrokinetic Mode in Colloids Laden Semiconductor Quantum Plasmas

Dispersion and absorption characteristics of electrokinetic wave in unmagnetised extrinsic semiconductor with streaming carriers are analytically investigated. By using quantum hydrodynamic model, a linear dispersion relation is derived for longitudinal electrokinetic wave in colloids laden semiconductor plasma under slow electrokinetic mode regime. Results indicate that quantum effect through Bohm potential significantly modifies the dispersion and absorption characteristics of electrokinetic wave spectrum. The outcome is hoped to add substantially to the present knowledge of wave spectrum of longitudinal electrokinetic wave in colloids laden quantum semiconductor plasma subjected to a dc electric field along the direction of wave propagation.

Influence of hot carriers on parametrically interacting polaron mode in semiconductors

In the present paper effect of hot carriers due to parametrically interacting electron- longitudinal optical phonons in polar semiconductor is analytically investigated. Presence of hot carriers is found to significantly modify the threshold and amplification characteristics in the presence of external magnetic fields. Expressions for threshold pump field required for the onset of polaron induced parametric interaction and amplification characteristics are explicitly derived. It is found that at moderate magnetic field and high carrier concentrations hot carriers affect threshold and amplification characteristics strongly. Resonance between polaron frequency and plasma frequency is found to be favourable for the minimum threshold field. Presence of hot carriers and magnetic field along with mass modulation effects are found to be additive and resulted into increment in the parametric gain. Typical dependence of parametric gain on magnetic field and carrier concentration could be utilized for the construction of optical switches.

Stimulated Brillouin scattering in semiconductors: Quantum effects

Present work is an attempt to find the influence of quantum effects on the Stimulated Brillouin Scattering in semiconductor plasmas using quantum hydrodynamic model. Third-order Brillouin susceptibility arising due to induced nonlinear current density in an n-type semiconductor crystal has been determined using coupled mode analysis. Effect of Bohm potential on the Brillouin gain coefficient is studied through the quantum corrections in classical hydrodynamic equations. It is found that the Bohm potential in the electron dynamics enhances the Brillouin gain. Reduction in the threshold pump intensity of the said process has been realized as a consequence of inclusion of quantum correction term.

Parametric dispersion and amplification characteristics of hot electron driven diffusive semiconductor plasmas

In this paper, an analytical expression for hot electron driven diffusion induced second-order susceptibility is obtained under non-resonant laser irradiation in magnetised semiconductor plasma. The hot electron effect due to intense pump modifies the momentum transfer collision frequency and diffusion coefficient which in turns enhances the dispersion as well as gain of the medium. The analysis deals with the qualitative behaviour of the anomalous parametric dispersion and the gain profile of the n-InSb semiconductor plasma.

Infra red active modes due to coupling of cyclotron excitation and LO phonons in polar semiconductor

Effects of free carrier concentration, external magnetic field and Callen effective charge on infra red active modes in a polar semiconductor have been analytically investigated using simple harmonic oscillator model. Callen effective charge considerably enhances reflectivity and shifts minima towards lower values of energy. Presence of magnetic field leads towards the coupling of collective cyclotron excitations with LO phonon giving rise to maximum reflectivity whereas cyclotron resonance absorption results into minimum reflectivity.

Steady State and Transient Gain Characteristics of the Stimulated Brillouin Scattered Mode in Quantum Semiconductor Plasmas

Using the quantum hydrodynamical model, the steady state and transient gain characteristics of the stimulated Brillouin scattered mode in semiconductor plasmas have been studied. The third-order Brillouin susceptibility due to a nonlinear current density and electrostriction of the medium have been determined using the coupled mode theory. The effect of the Bohm potential on the steady state and transient Brillouin gain coefficient was studied through the quantum corrections in the classical hydrodynamic equations. It was found that the Bohm potential in the electron dynamics enhances the steady-state and transient Brillouin gain coefficients. Reduction in the threshold pump intensity of the said process has been realized as a consequence of the inclusion of quantum correction term.