Presence Of Magnetostatic Field Research Articles

Piezoelectric Contributions to Parametric Amplification of Acoustical Phonons in Magnetized n-InSb Crystal

Abstract: Using the hydrodynamic model of semiconductor-plasmas and following the coupled-mode approach, we develop a theoretical formulation to study piezoelectric contributions to parametric amplification of acoustical phonons in magnetized n-InSb crystal. The origin of nonlinear interaction is assumed to lie in effective second-order optical susceptibility arising due to nonlinear induced current density and electrostrictive polarization of the medium. Expressions are obtained for threshold pump amplitude for the onset of parametric process and parametric gain coefficient (well above the threshold pump field) in the presence and absence of piezoelectricity and/or externally applied magnetostatic field. Numerical analysis is made for n-InSb crystal irradiated by 10.6 m pulsed CO2 laser. The piezoelectric contributions to three-wave parametric amplification process are only in the presence of magnetostatic field. The parametric gain coefficient is independent of doping concentration for the cases when either/both piezoelectricity and magnetostatic field are absent. Around resonance (electron-cyclotron frequency ~ pump frequency), the parametric gain coefficient in the presence of piezoelectricity is 102 times higher than that in the absence of piezoelectricity. The analysis establishes the technological potentiality of transversely magnetized n-InSb as the host for parametric devices, like parametric amplifiers and oscillators. Keywords: Parametric amplification, Acoustical phonons, Piezoelectricity, Electrostriction, n-InSb crystal. PACS numbers: 42.65.-k, 78.55.Cr, 71.38.-k, 52.35.Mw.

Piezoelectric Contributions to Optical Parametric Amplification of Acoustical Phonons in Magnetized Doped III–V Semiconductors

By employing the classic hydrodynamic model of semiconductor-plasmas, an analytical investigation is made to study the piezoelectric contributions to optical parametric amplification of acoustical phonons in magnetized doped III–V semiconductors. Assuming the origin of nonlinear interaction to lie in nonlinear-induced current density and electrostrictive polarization of the medium, expressions are obtained for threshold pump amplitude for the onset of parametric process and parametric gain coefficient in the presence and absence of piezoelectricity and/or externally applied magnetostatic field. Numerical analysis is made for n-InSb-CO2 laser system. The piezoelectric contributions to optical parametric amplification process are only in the presence of magnetostatic field. The parametric gain coefficient is independent of doping concentration for the cases when either/both piezoelectricity and magnetostatic field are absent. Around resonance (electron-cyclotron frequency~pump wave frequency), the parametric gain coefficient in the presence of piezoelectricity is 102 times higher than in the absence of piezoelectricity. The analysis establishes the technological potentiality of magnetized weakly piezoelectric doped III–V semiconductors as the hosts for fabrication of parametric amplifiers.

Modeling Field-Induced Transformations of Domain Walls in Soft-Magnetic Stripes

Magnetic-field-induced translation of domain walls (DWs) in nanowires and nanostripes is accompanied by oscillatory transformations of the structure of the DW if the field intensity exceeds the Walker breakdown value. Such transformations are analytically described with relevance to soft-magnetic nanostripes, where they are oscillations between a transverse DW, a vortex DW, and an antivortex DW. Two regimes of the stripe thicknesses separated by a critical length of macrospin approximation (of the order of tens of nanometers) are considered. A simple local approach to magnetostatics is used within which the presence of magnetostatic field is included at the stripe edges only via boundary conditions on the DW solutions to the Landau-Lifshitz-Gilbert equation. It enables description of the multi-vortex textures (DWs) in the regime of thick stripes for which validity of the analytical Thiele approach and micromagnetic simulation codes can be questionable because they use different time scales when evaluating magnetostatic and exchange fields. A method of qualitative description of the domain wall transformations in thinner than the critical length stripes is proposed.

Second-order optical susceptibility in doped III-V piezoelectric semiconductors in the presence of a magnetostatic field

A detailed analytical investigation of second-order optical susceptibility has been made in moderately doped III-V weakly piezoelectric semiconductor crystal, viz. n-InSb, in the absence and presence of an external magnetostatic field, using the coupled mode theory. The second-order optical susceptibility arises from the nonlinear interaction of a pump beam with internally generated density and acoustic perturbations. The effect of doping concentration, magnetostatic field and pump intensity on second-order optical susceptibility of III-V semiconductors has been studied in detail. The numerical estimates are made for n-type InSb crystals duly shined by pulsed 10.6 μm CO2 laser and efforts are made towards optimising the doping level, applied magnetostatic field and pump intensity to achieve a large value of second-order optical susceptibility and change of its sign. The enhancement in magnitude and change of sign of second-order optical susceptibility, in weakly piezoelectric III-V semiconductor under proper selection of doping concentration and externally applied magnetostatic field, confirms the chosen nonlinear medium as a potential candidate material for the fabrication of nonlinear optical devices. In particular, at B0 = 14.1 T, the second-order susceptibility was found to be 3.4 × 10-7 (SI unit) near the resonance condition.

Modulational instability of a laser beam in a piezoelectric semiconductor

Using a hydrodynamic model of a homogeneous plasma, the modulational instability of a laser beam has been studied when the laser beam interacts nonlinearly with a low-frequency transverse acoustic wave in the presence of a transverse magnetostatic field in a heavily doped n-type piezoelectric semiconductor. The instability results in the parametric amplification of the acoustic wave. The threshold electric field necessary for the onset of instability in the absence as well as in the presence of the magnetostatic field and the corresponding growth rates have been obtained analytically. The numerical analysis made for n-InSb at 77 K shows that the necessary laser field can be obtained by irradiating the crystal with a 10.6-μm CO2 laser. A large magnetostatic field lowers the threshold laser field appreciably.