Preparation and alignment of highly vibrationally excited molecules by CARP – chirped adiabatic Raman passage

Theoretical study of Raman chirped adiabatic passage by X-ray absorption spectroscopy: highly excited electronic states and rotational effects

Raman Chirped Adiabatic Passage (RCAP) is an efficient method to climb the vibrational ladder of molecules. It was shown on the example of fixed-in-space HCl molecule that selective vibrational excitation can thus be achieved by RCAP and that population transfer can be followed by X-ray Photoelectron spectroscopy [S. Engin, N. Sisourat, P. Selles, R. Taïeb, and S. Carniato, Chem. Phys. Lett. 535, 192-195 (2012)]. Here, in a more detailed analysis of the process, we investigate the effects of highly excited electronic states and of molecular rotation on the efficiency of RCAP. Furthermore, we propose an alternative spectroscopic way to monitor the transfer by means of X-ray absorption spectra.

Selective excitation of LI2 by chirped laser pulses with all possible interstate radiative couplings

We have numerically explored the feasibility and the mechanism of population transfer to the excited E  (1)Σ(g) electronic state of Li(2) from the v=0 level of the ground electronic state X  (1)Σ(g) using the A  (1)Σ(u) state as an intermediate. In this system, the use of transform limited pulses with a frequency difference greater than the maximum Rabi frequency does not produce population transfer when all possible radiative couplings are taken into account. We have employed two synchronous pulses far detuned from the allowed transition frequencies, mainly with the lower frequency pulse positively chirped, and both pulses coupling the successive pair of states, X-A and A-E. The adiabaticity of the process has been investigated by a generalized Floquet calculation in the basis of 12 field dressed molecular states, and the results have been compared with those obtained from the full solution of time dependent Schrödinger equation. The conventional representation of the process in terms of three (or four) adiabatic potentials is not valid. It has been found that for cases of almost complete population transfer in full calculations with the conservation of the vibrational quantum number, adiabatic passage is attained with the 12 state Floquet model but not with the six state model. The agreement between the full calculations and the 12 state Floquet calculations is generally good when the transfer is adiabatic. Another characteristic feature of this work is the gaining of control over the vibrational state preparation in the final electronic state by careful tuning of the laser parameters as well as the chirp rate sign. This causes time dependent changes in the adiabatic potentials and nonadiabatic transfers can be made to occur between them.

Polarization of molecular targets using infrared stimulated Raman adiabatic passage

We suggest that infrared stimulated Raman adiabatic passage, a coherent multiple excitation process, can be used to create a superposition of (2J+1) highly correlated M-state sublevels of a rigid rotor molecule with vibrational level v and rotational level J. This method employs the (v=0,J-2) to (v=2,J) S-branch transition, which is carried out in a counterintuitive manner in which the v=1 to v=2 transition is pumped prior to the v=0 to v=1 transition, causing nearly complete population transfer to the v=2 final level. We use perpendicular and parallel linearly polarized infrared excitation (biaxial excitation). Specifically, the perpendicular polarization connects the v=1 intermediate level to the final vibrational level v=2, and the parallel polarization connects the initial level v=0 to the intermediate level v=1. By this means we break the cylindrical symmetry for an ensemble of vibrationally excited molecules in a rovibrational eigenstate (v=2,J). The angular momentum polarization is determined by the relative phases rather than by the populations of the magnetic M-sublevels. For the phase correlated ensemble, the angular momentum polarization can be considered as a purely quantum mechanical effect. Using a fully general density matrix treatment, we illustrate this approach by considering a beam of carbon monoxide (CO) molecules. We find that significant polarization for J=2, 5, and 10 can be achieved with a cw infrared laser source having modest power (∼100 mW/mm(2)). We believe that this technique is a general one and may offer an experimentally accessible new platform for different applications, from scattering studies with M-state entangled ensembles of molecules to logic gate operations of a quantum computer.

Theoretical Study of Above-Threshold Dissociation on Diatomic Molecules by Using Nonresonant Intense Laser Pulses

The above-threshold dissociation of the ground state of a OH molecule under intense nonresonant laser pulses has been studied using the time-dependent Schrödinger equation with discrete variable representation. The applied field is assumed as a two-color mixed nonresonant laser pulses which has the nonresonant frequency omega and the overtone 2omega. After modulating the relative phase factor between the omega and 2omega pulse, we extracted a three-photon absorption peak or a five-photon absorption peak in the ATD spectrum.

Design of UV laser pulses for the preparation of matrix isolated homonuclear diatomic molecules in selective vibrational superposition states

The preparation of matrix isolated homonuclear diatomic molecules in a vibrational superposition state c0Phie=1,v=0+cjPhie=1,v=j, with large (|c0|2 approximately 1) plus small contributions (|cj|2<<1) of the ground v=0 and specific v=j low excited vibrational eigenstates, respectively, in the electronic ground (e=1) state, and without any net population transfer to electronic excited (e>1) states, is an important challenge; it serves as a prerequisite for coherent spin control. For this purpose, the authors investigate two scenarios of laser pulse control, involving sequential or intrapulse pump- and dump-type transitions via excited vibronic states Phiex,k with a dominant singlet or triplet character. The mechanisms are demonstrated by means of quantum simulations for representative nuclear wave packets on coupled potential energy surfaces, using as an example a one-dimensional model for Cl2 in an Ar matrix. A simple three-state model (including Phi1,0, Phi1,j and Phiex,k) allows illuminating analyses and efficient determinations of the parameters of the laser pulses based on the values of the transition energies and dipole couplings of the transient state which are derived from the absorption spectra.

Adiabatic Passage by Light-Induced Potentials in Polyatomic Molecules

In this paper we study the first application of adiabatic passage by light-induced potentials in polyatomic molecules. We analyze the effects of increasing the dimensionality of the system on the adiabatic requirements of the method and the role of intramolecular coupling among the vibrational modes. By using a model of two-dimensional displaced harmonic oscillators with or without rotation of the normal mode axis of the excited states (Duschinsky effect) we find that (1) it is possible to selectively transfer the vibrational population by adiabatic elongation of the bonds, (2) the adiabatic demands depend mainly on the energy barrier between the ground and excited electronic configurations, and not on the dimension of the system, (3) in the presence of intramolecular couplings the selective transfer can be achieved but at the cost of increasing the duration and/or the intensity of the pulses, which are needed to overcome small avoided crossings, and (4) the problem of selectivity becomes more important as the vibrational energy of the initial wave function increases.