Swati Dubey

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.

Nonlinear absorption and refractive index of a Raman scattered mode in magnetoactive centrosymmetric semiconductor plasmas

Abstract With the aid of a hydrodynamic model of a plasma, a detailed analytical investigation is made of the Raman instability of the Stokes component of the scattered wave in an obliquely magnetised (with respect to the direction of propagation) centrosymmetric semiconductor. The origin of the stimulated Raman scattering process lies in the third-order nonlinear optical susceptibility arising due to the induced nonlinear currently density and the interaction of the pump wave with the density fluctuations generated within the medium. The agreement in magnitude for third-order Raman susceptibility between our calculated values and the experimental as well as other theoretical values in found to be good. Using the couples mode theory of plasmas the total refractive index and absorption coefficient are determined via the effective susceptibility. The magnetic field and effective electric field are found to augment the refractive index. The absorption coefficient is found to be minimum when the pump is inclined at an angle of 12° to the magnetic field. The absorption coefficient reaches its minimum for the backscattered mode. The analysis establishes that a large nonlinear refractive index and a small absorption coefficient can easily be obtained in a magnetised centrosymmetric crystal which proves its potential as candidate material for fabrication of cubic nonlinear devices.

Polaron induced parametric interactions in magnetized semiconductors

In the framework of hydrodynamic model of semiconductor plasma, the parametric amplification due to polaron mode has been analytically investigated in a magnetized III–V semiconductor, viz. n-InSb. The origin of the phenomenon lies in the effective second-order optical susceptibility arising due to the induced nonlinear current density of the medium. Using the coupled-mode theory, the expressions for the parametric gain coefficient and the threshold amplitudes of the external electric field above which the parametric instability can occur are derived. The effect of the wave vector and the strength of the external magnetic field on the gain coefficient and the threshold amplitude of the pump electric field are analyzed. Reported results strongly suggest that at appropriate pump electric field, proper selection of the magnetic field not only lowers threshold pump field required for the onset of parametric excitation but also enhances gain effectively.

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.

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.

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.

Stimulated Raman Scattering of an Hybrid Pump Wave Propagating Obliquely in a Magnetoactive Centrosymmetric Semiconductor Plasma

Considering the hydrodynamic model of a semiconductor plasma, stimulated Raman scattering (SRS) of an hybrid pump wave propagating obliquely with the externally applied magnetic field in a centrosymmetric doped semiconductor plasma has been analytically investigated. The origin of SRS lies in the third-order nonlinear optical susceptibility arising due to the electron density perturbations and the molecular vibrations of the medium. The magnitude of third-order Raman susceptibility determined from the present analysis agrees well with the experimentally observed and theoretically quoted values. The steady-state Raman gain constant has been identified. The magnetic field is found to augment the gain constant. The gain constant increases with scattering angle and is maximum for the backscattered mode. Transmitted intensity of the scattered mode and Raman cell efficiency have also been deduced when the cell length is quite large compared to the pump wavelength. The cell effieiency is found to be maximum for the backscattered mode. The analysis established the possibility of optical phase conjugation in semiconductor plasma and the minimum cell length required for OPC to occur is found to be 60 μm.