Articles written in Pramana – Journal of Physics

    • Antibunching of photons in a coherent radiation field coupled to a non-degenerate parametric oscillator beyond rotating wave approximation


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      Under the classical (strong) pump condition, the Hamiltonian involving the signal and the idler modes of a non-degenerate parametric oscillator is exhibited. Without using the usual rotating wave approximation (RWA), the analytical solutions of the field operators are used to investigate the antibunching of photons of the input radiation field coupled to the non-degenerate parametric oscillator. By using the symbolic calculation, the antibunching of photons for both the signal and idler modes are investigated. In particular, the effects of the inclusion of rotating wave approximated terms on the antibunching of photons are clearly indicated. To substantiate the analytical results, the temporal evolution of signal photon and idler photons, and the antibunching effects of the signal and idler modes are investigated numerically by using the QuTip 3.1.0. The exact numerical results obtained by QuTip 3.1.0 matches extremely well with those of the analytical results. The present article and hence the analytical method might be of use for investigating the situations of having ultra-strongly and deep-strongly coupled systems where the possibilities of using RWA is completely ruled out.

    • Analytical investigation on the Autler–Townes splittings and the two-photon effects in a Doppler free signal lineshape of a double-λ type four-level system


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      By exploiting the pump–probe (signal) spectroscopy, the analytical expressions for the signal lineshapes of a four-level double-λ type system is obtained by solving the steady-state optical Bloch equations. By varying the pump frequencies (positions), the signal lineshapes are investigated as the function of signal detuning. The Autler– Townes effects and hence the ac-Stark splitting of the energy levels are exhibited when the pump is in on-resonanceposition. On the other hand, the off-resonance pump leads to the two-photon absorption and the shifts of the signal resonance peak positions. The analytical expressions for the imaginary part of the signal polarisation and hence theabsorption lineshapes are certainly useful for investigating various situations involving the pump intensity, decay time of energy levels and the spacing between the closely spaced levels. A few symbolic calculations involving the analytical expressions of the signal polarisation are provided to have the physical realisation. The data used for these calculations are partly theoretical in nature and are compatible with the real experiment. We neglect the Doppler effects and a semiclassical formalism of atom–field interaction is adopted throughout the investigation.

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