Praveen Aghamkar

Steady-state and transient Brillouin gain in magnetoactive narrow band gap semiconductors

Using electromagnetic treatment, a detailed analytical investigation is made to investigate both the steady-state and transient gains of Brillouin Stokes mode in magnetoactive piezoelectric III–V semiconductors. The Brillouin Stokes mode arises from the nonlinear interaction of an intense pump beam with the internally generated acoustic phonon mode and magnetoacoustic phonon mode in the finiteness of piezoelectricity and electrostriction. Following a coupled-mode approach, the third-order (Brillouin) susceptibility and steady-state and transient regime Brillouin gain of the backward Stokes mode are obtained in the presence and absence of an external static magnetic field. The dependence of the piezoelectricity, an external static magnetic field and pump pulse duration on growth rate of the backward Stokes mode has been analysed. The piezoelectricity and an externally applied static magnetic field substantially enhance both the steady-state and transient gain coefficients in a moderately doped III–V semiconductor. The enhanced transient gain coefficient can be greatly used in the compression of the backward scattered Stokes pulse.

Comparison between stimulated Raman and Brillouin scattering processes in magnetized doped III-V semiconductors

In the present paper, using the hydrodynamic model of semiconductor plasmas and following the coupled mode approach an analytical investigation of the stimulated Raman (SRS) and Brillouin (SBS) scatterings of the Stokes mode is undertaken in magnetoactive doped III-V semiconductors. These phenomena have been studied considering that the second-order forces responsible for them are different, viz., the finite differential polarizability gives rise to SRS, while the material properties like piezoelectricity and electrostrictive strain produces SBS in the medium. Gain coefficients, threshold pump intensities, and optimum pulse durations for the onset of SRS and SBS are estimated. The qualitative behavior of transient gain coefficients is found to be in agreement with the experimental and other theoretical observations. The proper selection of doping concentration and an externally applied magnetic field substantially enhances the gain coefficients of SBS and SRS processes. The ratio between the two gain constants indicates that for the same pump field SBS exhibits higher gain than SRS by two orders of magnitudes. The analysis explains satisfactorily the competition between stimulated Raman and Brillouin processes in the short- and long-pulse duration regimes. Numerical estimates have been made for n-type doped InSb crystal at 77K duly irradiated by 10.6&mgr;m CO2 laser.

Infrared Spectroscopic Study For Structural Investigation Of Lithium Lead Silicate Glasses

Lithium lead silicate glasses with composition 30Li2O⋅(70‐x)PbO⋅xSiO2 (where, x = 10, 20, 30, 40, 50 mol %) (LPS glasses) were prepared by normal melt quench technique at 1373 K for half an hour in air to understand their structure. Compositional dependence of density, molar volume and glass transition temperature of these glasses indicates more compactness of the glass structure with increasing SiO2 content. Fourier transform infrared (FTIR) spectroscopic data obtained for these glasses was used to investigate the changes induced in the local structure of samples as the ratio between PbO and SiO2 content changes from 6.0 to 0.4. The observed absorption band around 450–510 cm−1 in IR spectra of these glasses indicates the presence of network forming PbO4 tetrahedral units in glass structure. The increase in intensity with increasing SiO2 content (upto x = 30 mol %) suggests superposition of Pb‐O and Si‐O bond vibrations in absorption band around 450–510 cm−1. The values of optical basicity in these glasse...

Investigation Of Dispersive Conductivity And Dielectric Losses In Barium Bismuth Silicate Glasses

Barium bismuth silicate glasses (BBS glasses) with composition were prepared by normal melt quench technique. The dispersive conductivity and dielectric losses in these glasses were investigated by impedance spectroscopy. The analyses of ac conductivity spectra show a crossover from ion hopping conductivity to nearly constant loss (NCL) contribution in all the glasses. The variations in dielectric constant e*(ω) = e′(ω)‐ie″(ω) with frequency and temperature indicate an increase in electrode polarization, which reduces the dipolar relaxation effects in these glasses. The increased concentration of BaO in the glass composition reduces the dielectric losses in the present glasses.

Enhanced semiconductor photorefractivity in the presence of a magnetic field

Using single-defect single band mode, a large value of the exponential gain coefficient is obtained by degenerate two- picosecond light pulses in a photorefractive GaAs:EL2 crystal in the presence of an applied magneto-static field. The influences of a cd magnetic field on the temporal recording and erasure of the grating are analytically analyzed. A significant enhancement of the diffraction efficiency of the recorded hologram by a factor of 2 is obtained. The results are good qualitatively in agreement with the experimental observations.

Efficient parametric oscillation in the presence of a magnetic field

Using hydrodynamic model of a semiconductor -plasma and following the coupled-mode approach, an analytical investigation of excitation of a polaron mode is made in a direct gap III-V weakly polar, doped semiconductor in the presence of an applied magnetostatic field. The effect of magnetostatic fields on the basic operational characteristics of a parametric oscillator, viz., threshold condition and conversion efficiency has been critically analyzed. Numerical estimates are made for an n-InSb crystal at 5K duly irradiated by a pulsed 10.6 micrometers CO2 laser. The results are found to be in a good qualitative agreement with available experimental observations.

Embedded of Neodymium oxide nanoclusters in silica

The solgel process successfully prepared Nd2O3 / SiO2 nanocomposites. After drying in air at 85°C for three days, samples were heat treated, in air, at 750, 950, 1150 and 1250°C. Characterizations were made by, Infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. Mechanisms of neodymium oxide nano clusters formation in the densified silica matrix with respect to thermal treatment are discussed. XRD profiles confirm the crystallinity of the nanoclusters. The size of the nanoclusters was found in the range 15-30nm.