Electronic and vibrational population transfer in diatomic molecules as a function of chirp for different pulse bandwidths (original) (raw)
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We investigate theoretically the nonresonant excitation of vibrational levels in polar molecules by unipolar radiation pulses of duration much shorter than the characteristic period of the molecule's vibration. We consider several profiles of the potential of the interaction of atoms in a diatomic molecule and derive analytically the probabilities of the molecule's transition to excited vibrational states when driven by subcycle unipolar pulses. It is shown that the excitation efficiency is governed by the electric pulse area so that unipolar half-cycle pulses turn out to be the most efficient ones. We introduce the characteristic scale of the electric pulse area, which serves as a measure of the pulse action on the vibrational states of the molecule. The results are generalized to the interaction of excited vibrational and rotational states and it is shown that the behavior of the vibrational levels' populations versus the electric pulse area as well as the introduced characteristic scale stays valid.
Quantum dynamics of a diatomic molecule under chirped laser pulses
Journal of Physics B: Atomic, Molecular and Optical Physics, 1998
The photodissociation probability of a diatomic molecule is usually very small even under a strong field due to its anharmonicity. However, the progress in laser technology provides a chirped laser pulse to lower the threshold of the dissociation intensity. We investigate the quantum dynamics of a diatomic molecule under such a kind of pulse. It is found that there is a significant dissociation probability at moderate intensity for a diatomic molecule under a chirped pulse. The quantum dissociation probability is found to be suppressed with respect to the classical one for intensities above the dissociation threshold. Therefore the chirped pulse can efficiently dissociate a diatomic molecule.
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The Journal of Chemical Physics, 2000
A new method for the selective excitation of diatomic molecules in single vibrational states on excited electronic potentials by two-photon absorption is proposed. The method implies the use of two chirped strong pulse lasers detuned from the optical transition to an intermediate electronic state. We show under what scenarios the method is successful on the time-energy scale in which the pulses operate. They involved a long-time ͑nanosecond͒ weak-field regime and a short-time ͑picosecond͒ strong-field regime. The adiabatic representation in terms of energy levels or in terms of light-induced potentials is used to interpret the physical mechanism of the excitation. The efficiency and robustness of the scheme are demonstrated by the excitation of the ground vibrational state of the 1 ⌺ g (4s) electronic potential of the Na 2 molecule.
Rotational aspects of short-pulse population transfer in diatomic molecules
Chemical Physics Letters, 2004
A fully-selective population transfer scheme for diatomic molecules using short-duration (<ns) laser pulses is developed via the concept of light-induced potentials. It explicitly takes rotational degrees of freedom into account. We apply it to a specific Na 2 transition from the lowest ro-vibrationic state to a single ro-vibrational state of a doubly excited electronic state via an intermediate electronic state. The process insures total selective population transfer with pulses short compared to the molecule rotation time. However, an estimate of the multiphoton ionization rate using time-dependent density functional theory suggests that ionization may significantly adversely affect the transfer.
Cantori barriers in the excitation of a diatomic molecule by chirped pulses
Journal of Physics B: Atomic, Molecular and Optical Physics, 1999
We present a nonlinear dynamical study of a diatomic molecule under the interaction of chirped pulses. The step-like dissociation probability with respect to the initial vibrational states reflects the cantori barriers during the excitation process. The correspondence between classical and quantum cantori barriers is shown through classical phase trajectory and quantum Husimi distribution function. According to the results, the quantum suppression of classical dissociation in molecular excitation by chirped pulse disappears at some field parameters.
Solvent-Controlled Theory Analysis of Chirped Pulse Excitation of Molecules in Solutions
The Journal of Physical Chemistry B, 2001
A simple and physically clear approach to the interaction of intense chirped pulses with large molecules in solutions is developed: time-dependent rate equations for integral populations of electronic molecular states. For weak interaction, the time-dependent transition rates have a form of the Marcus electron-transfer rate. For larger interactions, the transition rates take into account the saturation effect similar to the transition rates in the solvent-controlled theory of electron-transfer reactions. The developed theory is a good approximation to a more sophisticated treatment (J. Chem. Phys. 1998, 109, 4523) which reproduces the effects observed in recent chirped pulse experiments.
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Physical Review A, 2010
We show numerically that it is possible to change the structure of a simple molecule, that is, a diatomic molecule, where the bond length is modified at a precise timing with symmetrically chirped laser pulses. In the adiabatic regime, the process is fully time reversible, making it possible to design slow vibrations with large bond elongations. The scheme relies on the preparation of a separable state of both nuclear and electronic degrees of freedom with predominant amplitude on the dissociative (antibonding) electronic wave function. Shorter laser pulses can be used to dynamically induce larger bond elongations, preparing a highly excited vibrational wave packet in the ground potential as the laser is switched off.
Pulse trains in molecular dynamics and coherent spectroscopy: a theoretical study
New Journal of Physics, 2009
Pulse trains (PTs) generated by sinusoidal phase masks emerged as a popular tool in the field of coherent control and have been applied successfully in many experiments. Although many attempts were made to throw light on the mechanism of the induced processes, it is not yet fully understood. Based on nonperturbative quantum dynamical calculations in the grid representation, we will elucidate the mechanism of PT excitation between anharmonic bound molecular electronic states. We extract general rules for the prediction of induced dynamics and the resulting spectra. The results allow us to outline perspectives for new applications, especially in the field of nonlinear spectroscopy.
Laser control of electronic transitions of wave packet by using quadratically chirped pulses
The Journal of Chemical Physics, 2005
An effective scheme is proposed for the laser control of wave packet dynamics. It is demonstrated that by using specially designed quadratically chirped pulses, fast and nearly complete excitation of wave packet can be achieved without significant distortion of its shape. The parameters of the laser pulse can be estimated analytically from the Zhu-Nakamura theory of nonadiabatic transition. If the wave packet is not too narrow or not too broad, then the scheme is expected to be utilizable for multidimensional systems. The scheme is applicable to various processes such as simple electronic excitation, pump-dump, and selective bond breaking, and it is actually numerically demonstrated to work well by taking diatomic and triatomic molecules ͑LiH, NaK, H 2 O͒ as examples.
Chemical Physics Letters, 2000
We have calculated the absorption spectrum of an intense chirped pulse exciting a solute molecule in a solvent. In general it depends on both the real and imaginary part of the susceptibility (a phase-dependent absorption in the nonstationary media). We have shown that the absorption spectrum directly re¯ects the time evolution of a vibrationally non-equilibrium population dierence in the ground and excited electronic states at the con®guration coordinate corresponding to instantaneous Franck±Condon transition, when measured using high-power and strongly chirped pulses. A method has been proposed for extracting this time evolution from the measured absorption spectrum. Ó