Prasanta Kumar Mahapatra

Electromagnetically induced grating in a three-level Ξ-type system driven by a strong standing wave pump and weak probe fields

We have analysed the properties of an electromagnetically induced grating formed in a Ξ-type three-level atomic system in the presence of a standing wave pump and travelling wave probe fields at resonant and off-resonant two-photon absorption. We have also shown the validity of this grating in an inhomogeneously broadened regime.

Nonlinear optical effects in a doubly driven four-level atom

We have studied nonlinear quantum optical effects in a doubly driven four-level atomic system in a homogeneously broadened regime. On application of two strong fields the system can be made to display double electromagnetically induced transparency (EIT) because of constructive quantum interference giving rise to nonlinear absorption at three-photon resonance condition. This fact may be used to obtain other phenomena like the effect of photon switching in a pulsed regime and large cross phase modulation (XPM) effect. We also show that the behaviour of spatial modulation of transparency of the weak probe beam in a three-level system interacted with a strong standing wave pump field can be dramatically changed in our four-level ladder type system. Here, strong coupling field acting on the uppermost transition is represented by a standing wave whereas strong pump and weak probe fields acting successively on the lower transitions are represented by travelling waves. The effect of double EIT on nonlinear light generation based on the four-wave-mixing (FWM) technique is also investigated. We have examined that the four wave mixing efficiency can be effectively controlled by varying the strength of the pump field.

Vacuum induced interference effect in probe absorption in a driven Y-type atom

We have analyzed the properties of weak probe absorption in a closed four-level Y-type system driven by a coherent driving field. The system with two nearly degenerate uppermost levels interacting with the same modes of the vacuum radiation field exhibits the interference effect between the spontaneous decay channels. The phenomenon of this quantum interference can significantly change the absorptive response of the weak probe field. On varying the amplitude of the resonant driving field, in the absence of incoherent pumping in the upper transitions the system can display probe transparency as well as enhanced absorption peak under the condition of resonant detuning of the probe field. With the application of incoherent pumping to the system the phenomenon of symmetric light amplification with two distinct gain peaks one each at the positions of Autler–Townes resonances can be achieved in the presence of the decay-interference effect. We have also shown that the unidirectional incoherent pumping mode is necessary for the evolution of probe gain.

Corrigendum: Coherent control of localization of a three-level atom by symmetric and asymmetric superpositions of two standing-wave fields

A scheme for one-dimensional localization of a three-level atom is proposed by employing a modified technique for the formation of a standing-wave regime using two standing-wave fields. In the present system, precise position information of the atom can be achieved by measuring the population of the excited state, which can be efficiently controlled by the symmetric and the asymmetric superpositions of two standing-wave fields in the presence of constructive quantum interference. Our results highlight that, depending upon the effect of asymmetric superposition, the proposed scheme may provide a promising way to obtain various types of single-peak and double-peak localizations of the atom either in a one-wavelength range or in a half-wavelength range with appropriate values of the Rabi frequencies, detunings and spatial phase shifts of the coupling fields.

Control of the spontaneous emission spectrum in a driven N-type atom by dynamically induced quantum interference

The modification of the spontaneous emission spectrum has been studied in this paper in a four-level doubly driven N-type atomic system. In the presence of two coherent fields, emphasis has been given to studying the spectral distribution of spontaneous emission in the relaxation process of the initially prepared excited level. The phenomenon of quantum interference dynamically induced in the system by these fields can significantly change the spontaneous emission spectrum. We have shown the emergence of a two-peak spectrum where two widely separated symmetric peaks are associated with a sharp dark line at their mid-position. At different dynamic conditions, we have also shown that two symmetric peaks may appear in the spectrum with an extended dark zone between them. Depending on the values of the Rabi frequencies and the detunings of the external fields, one can achieve a large enhancement of very narrow spectral components within the spontaneous emission line shape under different conditions. The phenomenon of suppression of spectral line and the selective cancellation of spontaneous emission have also been discussed. The results shown in various cases are analysed by considering all possible dressed states corresponding to the bare state model. The influence of collision-induced effects on the spontaneous emission spectrum is investigated as a conditional case.

Current density in generalized Fibonacci superlattices under a uniform electric field

We present an exhaustive study on tunneling and electrical conduction in an electrically biased GaAs-Al(y)Ga(1-y)As generalized Fibonacci superlattice. The study is based on transfer matrix formalism using an Airy function approach and provides an exact calculation of the current density in the case of quasi-periodic multibarrier systems. The results suggest the use of such quasi-periodic systems in perfect band-pass or band-eliminator (of extremely low width) circuitry. We have clearly demonstrated the resonance-type peaks and negative differential conductivity regimes in such systems. It has also been found that quasi-periodicity favors sharp negative differential conductivity peaks compared to those in periodic superlattices and thus have profound importance in device applications.

Role of incoherent pumping scheme on gain without population inversion in four-level systems

We have studied gain without population inversion in two similar four-level systems by employing semiclassical density-matrix formalism. If the incoherent pumping process is not taken into account, both systems can be visualized as an ideal V-type system. Along with the application of strong pump and weak probe fields, an incoherent pump field is added to each of the systems in a different configuration. It has been shown that the different mechanisms of application of an incoherent pump to the system can appreciably change the population difference between the energy levels of the strongly driven transition and results in the evolution of inversionless gain either at the line center or at the sidebands on probe detuning. The effect of inhomogeneous broadening on the probe gain has also been studied.

Structural, electrical and dielectric properties of Na2W3O10 ceramic

Polycrystalline samples of Na2W3O10 are prepared by a solid-state reaction technique. Preliminary X-ray powder diffraction studies of the compound suggest the formation of single-phase material in the triclinic crystal system. Measurement of dielectric constant (e) and tangent loss (tanδ) as a function of temperature have shown dielectric anomaly at Tc=258 °C, suggesting the transition to be of the first order. Variation of dc conductivity with temperature shows that the conductivity of the material is temperature dependent and increases with the increase in temperature.

Lifetime of resonant tunnelling states in multibarrier systems

Abstract We have studied the variation of the resonant tunnelling lifetime with resonant energies for multibarrier systems (MBS) consisting of rectangular barrier type potentials and going beyond the usual double barrier case. Among other things, this variation shows a special kind of minima for MBS with more than three barriers.

Structural and electrical properties of modified lead germanate ferroelectrics

Abstract Polycrystalline samples of modified lead germanate, Pb 4.95 A 0.05 Ge 2.5 Ti 0.5 O 11 ( A = Ca , Sr , Ba ), were prepared using solid-state reaction techniques. X-ray powder diffraction studies of the compounds suggest the formation of single phase materials of trigonal crystal structure at room temperature. Detailed studies of the dielectric constant (e) and loss (tan δ) of the compounds, both as a function of frequency (2 x 10 2 − 10 6 Hz) at room temperature and temperature (from room temperature to 200 °C) at 10, 100 and 1000 kHz, exhibit a ferroelectric diffuse phase transition. The transition temperature is found to decrease with Ba, Sr and Ca doping at the Pb site. The biasing field and temperature dependence of dc electrical conductivity were measured for all the compounds. The nature of the ferroelectric phase transition was checked by measuring the temperature dependence of the polarization.