The dependence of initial states on the excitation of NO molecules by chirped infrared laser pulses (original) (raw)
Related papers
Excitation of the NO molecule by chirped infrared laser pulses
Physical Review A, 1999
To explore the insights of recent experiments on the excitation of the NO molecule by chirped subpicosecond IR pulses, a corresponding theoretical study is presented. The agreements between experimental and theoretical results show the importance of the full-dimensional quantum-mechanical calculation.
Selective excitation of diatomic molecules by chirped laser pulses
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.
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.
Chirped pulse excitation in condensed phases involving intramolecular modes. II. Absorption spectrum
The Journal of Chemical Physics, 2002
We have calculated the absorption spectrum of an intense chirped pulse exciting a solute molecule in a solvent. The excitation of quantum intramolecular modes has been also taken into account. In general absorption depends on both the real and imaginary part of the susceptibility ͑a phase-dependent absorption in the nonstationary media͒. We have shown that for strongly chirped pulses, the absorption spectrum can be expressed by the difference of the convolutions of the ''intramolecular'' absorption and luminescence spectra with the instantaneous population wave packets in the ground and excited electronic states, respectively. Incorporating of optically active high-frequency intramolecular vibrational modes eliminates the qualitative discrepancies between experimental and calculated absorption spectra which occurred in the model of one vibronic transition.
Infrared–x-ray pump-probe spectroscopy of the NO molecule
Physical Review A, 2005
Two color infrared-x-ray pump-probe spectroscopy of the NO molecule is studied theoretically and numerically in order to obtain a deeper insight of the underlying physics and of the potential of this suggested technology. From the theoretical investigation a number of conclusions could be drawn: It is found that the phase of the infrared field strongly influences the trajectory of the nuclear wave packet, and hence, the x-ray spectrum. The trajectory experiences fast oscillations with the vibrational frequency with a modulation due to the anharmonicity of the potential. The dependences of the x-ray spectra on the delay time, the duration, and the shape of the pulses are studied in detail. It is shown that the x-ray spectrum keep memory about the infrared phase after the pump field left the system. This memory effect is sensitive to the time of switching-off the pump field and the Rabi frequency. The phase effect takes maximum value when the duration of the x-ray pulse is one-fourth of the infrared field period, and can be enhanced by a proper control of the duration and intensity of the pump pulse. The manifestation of the phase is different for oriented and disordered molecules and depends strongly on the intensity of the pump radiation.
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
The Journal of Chemical Physics, 2003
We study the dynamics of two-photon nonresonant electronic excitation of diatomic molecules driven by chirped pulses. While the majority of the experimental results address the role of the chirp for fixed pulse bandwidth, we analyze the possibility of selective excitation for fixed time, as a function of the pulse bandwidth, depending on the sign of the chirp. With strong picosecond pulses and positive chirp it is shown that the dynamics always prepare the molecule in the ground vibrational level of the excited electronic state. The robustness of the dynamics inherits the properties of an effective Landau-Zener crossing. For negative chirp the final state is very sensitive to the specific pulse bandwidth. The dynamics of the system follow a complex convoluted behavior, and the final state alternates between low vibrational levels of the excited electronic state and excited vibrational levels of the ground potential, which become increasingly more excited with increasing bandwidth. The final electronic populations follow a double-period oscillatory behavior. We present a model based on sequential independent crossings which correlates the long-oscillation period with changes in the final vibrational state selected. We show that the short-oscillation period is related with nonadiabatic effects that give rise to fast dynamic Rabi flipping between the electronic states, providing only information of the field-molecule effective coupling. Although the short-oscillation period partially masks the expected results of the final populations, we show that it is still possible to retrieve information from the long-oscillation period regarding the frequencies of the electronic potentials. In order to do so, or in order to control the outcome of the dynamics, it is necessary to perform experiments scanning very different pulse bandwidths, and we propose a possible experimental implementation. All the numerical results of the paper are calculated for a model of the Na 2 dimer.
Physical Review A, 2004
This theoretical paper presents numerical calculations for photoassociation of ultracold cesium atoms with a chirped laser pulse and detailed analysis of the results. In contrast with earlier work, the initial state is represented by a stationary continuum wavefunction. In the chosen example, it is shown that an important population transfer is achieved to ≈ 15 vibrational levels in the vicinity of the v=98 bound level in the external well of the 0 − g (6s + 6p 3/2 ) potential. Such levels lie in the energy range swept by the instantaneous frequency of the pulse, thus defining a "photoassociation window". Levels outside this window may be significantly excited during the pulse, but no population remains there after the pulse. Finally, the population transfer to the last vibrational levels of the ground a 3 Σ + u (6s + 6s) is significant, making stable molecules. The results are interpreted in the framework of a two state model as an adiabatic inversion mechanism, efficient only within the photoassociation window. The large value found for the photoassociation rate suggests promising applications. The present chirp has been designed in view of creating a vibrational wavepacket in the excited state which is focussing at the barrier of the double well potential.
We apply the ‘classic’ semiclassical initial value representation (SC-IVR) approach to describe rotational excitation of non-polar diatomic molecules by intense short non-resonant laser pulses. We also investigate the applicability of the quantum mechanical sudden approximation. It is found that the SC-IVR approach gives accurate rotational excitation probabilities in regimes where the sudden approximation fails. Primitive semiclassical wavefunction propagation is used to illustrate the phenomenon of angular focussing of rotation states by strong pulses.