Extracting the polarizability anisotropy from the transient alignment of HBr

Formulation and Implementation of Frequency-Dependent Linear Response Properties with Relativistic Coupled Cluster Theory for GPU-Accelerated Computer Architectures

We present the development and implementation of relativistic coupled cluster linear response theory (CC-LR), which allows the determination of molecular properties arising from time-dependent or time-independent electric, magnetic, or mixed electric-magnetic perturbations (within a common gauge origin for the magnetic properties) as well as taking into account the finite lifetime of excited states in the framework of damped response theory. We showcase our implementation, which is capable to offload the computationally intensive tensor contractions characteristic of coupled cluster theory onto graphical processing units, in the calculation of (a) frequency-(in)dependent dipole-dipole polarizabilities of IIB atoms and selected diatomic molecules, with a particular emphasis on the calculation of valence absorption cross sections for the I2 molecule; (b) indirect spin-spin coupling constants for benchmark systems such as the hydrogen halides (HX, X = F-I) as well the H2Se-H2O dimer as a prototypical system containing hydrogen bonds; and (c) optical rotations at the sodium D line for hydrogen peroxide analogues (H2Y2, Y = O, S, Se, Te). Thanks to this implementation, we are able to show the similarities in performance, but often the significant discrepancies, between CC-LR and approximate methods such as density functional theory. Comparing standard CC response theory with the flavor based upon the equation of motion formalism, we find that for valence properties such as polarizabilities, the two frameworks yield very similar results across the periodic table as found elsewhere in the literature; for properties that probe the core region, such as spin-spin couplings, on the other hand, we show a progressive differentiation between the two as relativistic effects become more important. Our results also suggest that as one goes down the periodic table, it may become increasingly difficult to measure pure optical rotation at the sodium D line due to the appearance of absorbing states.

Scattering of adiabatically aligned molecules by nonresonant optical standing waves

We study the effect of rotational state-dependent alignment in the scattering of molecules by optical fields. CS₂ molecules in their lowest few rotational states are adiabatically aligned and transversely accelerated by a nonresonant optical standing wave. The width of the measured transverse velocity distribution increases to 160 m/s with the field intensity, while its central peak position moves from 10 to -10 m/s. These changes are well reproduced by numerical simulations based on the rotational state-dependent alignment but cannot be modeled when ignoring these effects. Moreover, the molecular scattering by an off-resonant optical field amounts to manipulating the translational motion of molecules in a rotational state-specific way. Conversely, our results demonstrate that scattering from a nonresonant optical standing wave is a viable method for rotational state selection of nonpolar molecules.

Effect of aligning pulse train on the orientation and alignment of a molecule in presence of orienting pulse

Field-free molecular alignment is studied theoretically in presence of orienting laser pulse and a delayed Infrared laser (IRL) pulse train. The pulse shapes taken are sine square (sin²) and square. The degree of alignment can be significantly enhanced by the combination of orienting pulse and IRL pulse train compared with only IRL pulse train. Special emphasis is laid on time delay between orienting and aligning pulse, the width and shape of the pulse train. By adjusting the time delay, width and intensity of coupling laser one can suppress a population of particular state while simultaneously enhancing the population of desired states.

Precise Access to the Molecular-Frame Complex Recombination Dipole through High-Harmonic Spectroscopy

We report on spectral intensity and group delay measurements of the highest-occupied molecular-orbital (HOMO) recombination dipole moment of N_{2} in the molecular-frame using high harmonic spectroscopy. We take advantage of the long-wavelength 1.3  μm driving laser to isolate the HOMO in the near threshold region, 19-67 eV. The precision of our group delay measurements reveals previously unseen angle-resolved spectral features associated with autoionizing resonances, and allows quantitative comparison with cutting-edge correlated 8-channel photoionization dipole moment calculations.

Pulse train induced rotational excitation and orientation of a polar molecule

We investigate theoretically the rotational excitation and field free molecular orientation of polar HBr molecule, interacting with train of ultrashort laser pulses. By adjusting the number of pulses, pulse period and the intensity of the pulse, one can suppress a population while simultaneously enhancing the desired population in particular rotational state. We have used train of laser pulses of different shaped pulse envelopes. The dynamics and orientation of molecules in the presence of pulse train of different shapes is studied and explained.

Controlling rotational dynamics and alignment of molecule by infrared laser pulse

We investigate the effects of delayed infrared laser (IRL) pulse shape on the non-adiabatic rotational excitation and alignment of a polar molecule. We suggest a control scheme for choosing populations of molecular rotational states by wave packet interference. The rotational wave packets of polar molecule (here HBr) excited non-adiabatically by orienting pulse is controlled actually using the second delayed IRL pulse. By adjusting the time delay between the two laser pulses and the shape of delayed IRL pulse, constructive or destructive interference among these wave packets enables the population to be enhanced or repressed for the specific rotational state. We have used fourth order Runge-Kutta method to study the non-adiabatic rotational excitation (NAREX) dynamics.

All-optical molecular orientation

We report clear evidence of all-optical orientation of carbonyl sulfide molecules with an intense nonresonant two-color laser field in the adiabatic regime. The technique relies on the combined effects of anisotropic hyperpolarizability interaction and anisotropic polarizability interaction and does not rely on the permanent dipole interaction with an electrostatic field. It is demonstrated that the molecular orientation can be controlled simply by changing the relative phase between the two wavelength fields. The present technique brings researchers a new steering tool of gaseous molecules and will be quite useful in various fields such as electronic stereodynamics in molecules and ultrafast molecular imaging.