Chandan Kumar Mondal

Optimal control theory in adaptive simulated annealing technique: optimisation of laser pulse for selective vibrational excitations and photo-dissociation of HBr+

An optimisation method using optimal control theory based adaptive simulated annealing technique has been explored to get optimised laser pulses for selective vibrational excitations and photo-dissociation of the HBr+ in its ground electronic state. Potential energy curve of the system has been obtained by coupled cluster singles and doubles (CCSD) level calculation, using aug-cc-pVTZ as basis set. To have a simple pulse, a limited number of parameters is chosen as variables and the technique so developed works well. The study is extended with chirping field frequency to explore the effect of chirping in dynamics.

Laser pulse design using optimal control theory-based adaptive simulated annealing technique: vibrational transitions and photo-dissociation

We have designed and optimised a combined laser pulse using optimal control theory-based adaptive simulated annealing technique for selective vibrational excitations and photo-dissociation. Since proper choice of pulses for specific excitation and dissociation phenomena is very difficult, we have designed a linearly combined pulse for such processes and optimised the different parameters involved in those pulses so that we can get an efficient combined pulse. The technique makes us free from choosing any arbitrary type of pulses and makes a ground to check their suitability. We have also emphasised on how we can improve the performance of simulated annealing technique by introducing an adaptive step length of the different variables during the optimisation processes. We have also pointed out on how we can choose the initial temperature for the optimisation process by introducing heating/cooling step to reduce the annealing steps so that the method becomes cost effective.

Theoretical study of Zeno and anti-Zeno effects on photodissociation dynamics: A model approach

Zeno and anti-Zeno effects in the evolution of the multi-photonic dissociation dynamics of the diatomic molecule HBr+ owing to repeated measurements demand if the system in the initial state have been studied. The effects have been calculated numerically for the case of vibrational population transfer and dissociation dynamics of HBr+ taking it as a model. We use time-dependent Fourier grid Hamiltonian (TDFGH) method as a mathematical tool in presence of intense radiation field as perturbation. The effects have been explored through a probable mechanism of population transfer from the ground vibrational state to the different upper vibrational states which ultimately go to the dissociation continuum. The results show significant differences in the mechanism of population transfer and the significant role of time interval of measurement (τ) in Zeno and anti-Zeno effects. In case of survival probability of ground vibrational states, there is Zeno effect when the frequency of the laser to which the molecule is submitted is near the vibrational v=0 to v=1 resonance, while there is anti-Zeno effect if it is far from this resonance.

Modeling Photo-dissociation Dynamics of HBr+ by Vibrational Wave-packet Formalism

Photo dissociation dynamics of diatomic molecular ion HBr+ interacting with ultra fast laser pulses of different envelop function has been presented both in zero and non zero temperature environment. The calculations pertain primarily to the ground electronic state of the molecular ion HBr+. The used potential of HBr+ is calibrated with the help of the ab initio theoretical calculation at the CCSD/6-311++G(3df, 2pd) level and then fitted with appropriate Morse parameters. The numerical bound states vibrational eigenvalues obtained by the time independent Fourier Grid Hamiltonian method have been compared with analytical values of the fitted Morse potential. The effect of temperature, pulse envelops function, and light intensity on the dissociation process has been explored.

Thermal modulation in Zeno and anti-Zeno effects on quantum measurement

ABSTRACT We have proposed the mathematical formulations of quantum Zeno and anti-Zeno effects at non-zero temperature on vibrational population transfer and dissociation of a diatomic system. The proposed formulation has been tested for diatomic systems HBr+ and HI using time-dependent Fourier grid Hamiltonian method. The effect of temperature on the dynamics is incorporated through the population distribution at different vibrational states following Boltzmann distribution formula. It has been found that with increase in temperature Zeno effect increases and anti-Zeno effect decreases in case of survival probability on ground vibrational state. In case of dissociation, with increase in temperature Zeno effect increases while anti-Zeno effect remains almost same.

Effect of Environment on Photo-detachment Dynamics of Halide Ions: A Model Approach

A two dimensional model approach for the photodetachment dynamics of closed shell anionic systems in presence of external light field have been proposed in the context of polar environmental media. The effects of strong coupling between the solvent polarization and the extra charge in the system were studied by a simple model. The electronic states of concerned halide ions are represented by a two dimensional model Hamiltonian with a potential V(x, y) = −V 0e−σ(x 2 + y 2). The time dependent Fourier grid Hamiltonian method have been used to follow the detachment process with fairly high intensities of light. The environmental effects on the dynamics are sought to be modeled by two different ways. The first one was the presence of polar solvents which perturb the energy levels of anionic systems by changing the effective potential surface and the second one was allowing the fluctuation of the well depth randomly to mimic the system in a more realistic view point. The average detachment rate constant is calculated as a function of important parameters of the used light field to explain the effects of solvent field on the dynamical behavior of dipole bound anionic system at least in a qualitative way.