Maxim Artamonov

Theory of three-dimensional alignment by intense laser pulses.

We introduce a theoretical framework for study of three-dimensional alignment by moderately intense laser pulses and discuss it at an elementary level. Several features of formal interest are noted and clarified. Our approach is nonperturbative, treating the laser field within classical and the material system within quantum mechanics. The theory is implemented numerically using a basis set of rotational eigenstates, transforming the time-dependent Schrodinger equation to a set of coupled differential equations where all matrix elements are analytically soluble. The approach was applied over the past few years to explore different adiabatic and nonadiabatic three-dimensional alignment approaches in conjunction with experiments, but its formal details and numerical implementation were not reported in previous studies. Although we provide simple numerical examples to illustrate the content of the equations, our main goal is to complement previous reports through an introductory discussion of the underlying theory.

Molecular Focusing and Alignment with Plasmon Fields

We show the possibility of simultaneously aligning molecules and focusing their center-of-mass motion near a metal nanoparticle in the field intensity gradient created by the surface plasmon enhancement of incident light. The rotational motion is described quantum mechanically while the translation is treated classically. The effects of the nanoparticle shape on the alignment and focusing are explored. Our results carry interesting implications to the field of molecular nanoplasmonics and suggest several potential applications in nanochemistry.

Time-Dependent, Optically Controlled Dielectric Function.

We suggest optical modulation of the dielectric function of a molecular monolayer adsorbed on a metal surface as a potential means of controlling plasmon resonance phenomena. The dielectric function is altered using a laser pulse of moderate intensity and linear polarization to align the constituent molecules. After the pulse, the monolayer returns to its initial state. Time-dependent, optically controlled dielectric function is illustrated by molecular dynamics calculations.

Axis-dependence of molecular high harmonic emission in three dimensions

High-order harmonic generation in an atomic or molecular gas is a promising source of sub-femtosecond vacuum ultraviolet coherent radiation for transient scattering, absorption, metrology and imaging applications. High harmonic spectra are sensitive to Ångstrom-scale structure and motion of laser-driven molecules, but interference from radiation produced by random molecular orientations obscures this in all but the simplest cases, such as linear molecules. Here we show how to extract full body-frame high harmonic generation information for molecules with more complicated geometries by utilizing the methods of coherent transient rotational spectroscopy. To demonstrate this approach, we obtain the relative strength of harmonic emission along the three principal axes in the asymmetric-top sulphur dioxide. This greatly simplifies the analysis task of high harmonic spectroscopy and extends its usefulness to more complex molecules.

Three-dimensional laser alignment of polyatomic molecular ensembles

We explore the physics of alignment and three-dimensional alignment of polyatomic molecular ensembles in moderately-intense laser fields. To that end we develop a purely classical approach to molecular alignment and compare its results with those of quantum mechanical calculations in appropriate limits, finding qualitative agreement. The method is applied to explore a new phenomenon in strong field coherent control that is unique to the ensemble case, namely the formation of organized assembly due to induced dipole–induced dipole interactions at sufficiently large intensities or/and densities. The effects of the laser field polarization, its intensity, and the initial rotational temperature on the degree of alignment and the translational and orientational order of the assembly are investigated.

Field-free asymmetric top alignment and rotational revivals using high harmonic generation

Using high harmonic generation (HHG), we probe the nonadiabatic revival structure in the asymmetric top sulfur dioxide. We find that HHG is sensitive to molecular alignment about different axes as well as of partial revivals.