Parvendra Kumar

Modulation instability of ultrashort pulses in quadratic nonlinear media beyond the slowly varying envelope approximation

We report a modulational instability (MI) analysis of a mathematical model appropriate for ultrashort pulses in cascaded-quadratic-cubic nonlinear media beyond the so-called slowly varying envelope approximation. The study shows the possibility of controlling the generation of MI and formation of solitons in a cascaded-quadratic-cubic medium in the few-cycle regimes.

Optical dipole force on ladderlike three-level atomic systems induced by few-cycle-pulse laser fields

We report a study on the optical dipole force in a ladder like three level atomic systems in the context of coherent population transfer with the chirped few-cycle-pulse laser fields. The phenomenon of coherent population transfer is investigated by numerically solving the appropriate density matrix equations beyond the rotating wave approximation. On the other hand, optical dipole force is calculated by numerically solving the force equation and density matrix equations self-consistently. By analysing the centre-of-mass motion, it is shown that the optical dipole force with chirped pulses may be used for focusing and defocusing of atoms in an atomic beam similar to the near or non-resonant optical dipole force. Moreover, the robustness of the population transfer against the variation of the pulse parameters and the effect of the variation of the Rabi frequencies and the chirp rates on the optical dipole force are also investigated. The proposed scheme may open new perspectives in the focusing and de-focusing of atoms and molecules in an atomic beam, since this scheme mitigates the demand for the generation of transform-limited pulse laser fields at arbitrary frequencies.

Simultaneous control of optical dipole force and coherence creation by super-Gaussian femtosecond pulses inΛ-like atomic systems

We report a study on the optical dipole force on a beam of neutral three-level like atomic system induced by a femtosecond super-Gaussian pulse. We show that maximum coherence between the ground state |1> and the excited state |2> could be achieved using a train of femtosecond pulses. In addition, it is possible to control the trajectory of the atoms in an atomic beam by using the same scheme. The robustness of the scheme against the variation of the pulse parameters is also investigated.

Ultrafast and selective coherent population transfer in four-level atoms by a single nonlinearly chirped femtosecond pulse

We report a simple scheme to achieve ultrafast and selective population transfer in four-level atoms by utilizing a single nonlinearly chirped femtosecond pulse. It is demonstrated that the almost complete population may be transferred to the preselected state of atoms just by manipulating the so-called frequency offset parameter. The robustness of the scheme against the variation of laser pulse parameters is also investigated. The proposed scheme may be useful for selective population transfer in molecules.

Frequency-modulated few-cycle optical-pulse-train-induced controllable ultrafast coherent population oscillations in two-level atomic systems

We report a study on the ultrafast coherent population oscillations (UCPO) in two level atoms induced by the frequency modulated few-cycle optical pulse train. The phenomenon of UCPO is investigated by numerically solving the optical Bloch equations beyond the rotating wave approximation. We demonstrate that the quantum state of the atoms and the frequency of UCPO may be controlled by controlling the number of pulses in the pulse trains and the pulse repetition time respectively. Moreover, the robustness of the population inversion against the variation of the laser pulse parameters is also investigated. The proposed scheme may be useful for the creation of atoms in selected quantum state for desired time duration and may have potential applications in ultrafast optical switching.

Gaussian and sinc-shaped few-cycle-pulse-driven ultrafast coherent population transfer inΛ-like atomic systems

We report and propose a simple scheme to achieve efficient and fast coherent population transfer (CPT) by utilizing either a nonlinearly chirped Gaussian shaped few-cycle laser pulse or an unchirped sinc-shaped few-cycle laser pulse. The proposed scheme is shown to be fairly robust against the variation of the laser parameters such as temporal pulse width, chirp rates, carrier envelope phases and Rabi frequencies. We find that compared to the so-called stimulated Raman adiabatic passage (STIRAP) technique, our scheme for complete population transfer with few-cycle Gaussian shaped laser pulses requires less pulse area.

Extreme Nonlinear Optics: Effect of Carrier Envelope Offset Phase on the Dynamics of Two Level Atomic Systems

We study the effect of carrier envelope offset (CEO) phase of a few cycle pulse on the dynamics of two‐level systems in the domain of extreme nonlinear optics. Strong dependence of polarization on the CEO phase is observed. Intensity of different high harmonics and their interference is clearly seen to be dependent on the CEO phase of the optical pulses. Our results show that the final state of the atomic system, just after the few cycle optical pulse has passed through the system, depends very strongly on the CEO phase of the pulse.