Sanjukta Ghosh

On aspects of modulational amplification in noncentrosymmetric and centrosymmetric semiconductors

Abstract A comparison of the modulational growth rates arising due to transverse modulational instability has been made in noncentrosymmetric (NCS) and centrosymmetric (CS) semiconductors. The retardation effect due to the noncentrosymmetricity of the medium has been investigated using an electromagnetic approach. The threshold field E0 th required to obtain a modulational amplification process has also been estimated. Both the modulational gain factor and E0 th are found to be strongly dependent on the carrier concentration of the medium. The retardation effect due to finite Д(2) in NCS crystals is found to play a more significant role in the case of a lightly doped medium. The modulational gain constant is found to undergo absorption in the strongly dispersive regime of the acoustic mode in the case of NCS crystals, while it grows appreciably under similar conditions in a CS medium.

Probing the Effects of SHI and Doping-Induced Defects in Nanocrystalline Spinel Ferrites

Different types of defects have been introduced in ferrite thin films and bulk (powder) systems by implementing different methods namely swift heavy ion irradiation, impurity doping.and mechanical milling. Swift heavy ions (190 MeV Au ions and 150 MeV Ni ions) induced defects in nanocrystalline ferrite thin films arise due to formation of the latent tracks and the point defects. We have elaborately discussed the observed effects in magnetic, surface and electrical properties of ferrite thin films irradiated with SHI. The effects of point defects in impurity doping (In ions) and the effects of dislocations in mechanical milling (for different hours) have also been discussed in this paper.

EMI/EMC in Microwave and Millimeter Wave Receivers

The IF chain of a microwave and millimeter wave receiver is subject to VHF EMI problems, which often limit the useful sensitivity of microwave and millimeter wave superheterodyne receivers. In spectrum analyzer design, special care is taken to shield the IF chain adequately and filter out EMI from entering receiver front end. However, in practical radar receivers, radiometers and microwave link terminals, the protection against EMI may often be inadequate. Some of the problems were studied at Calcutta during the studies on radio wave propagation characteristics in the VHF, UHF, microwave and millimeter wave bands. The results obtained are presented in this paper.