Macroscopic Spin-Orbit Interaction through Strong-Field Pumping of Inhomogeneously Aligned Molecular Ensemble

Abstract

We study the strong-field interaction of a helical bi-chromatic pump with an anisotropic and inhomogeneous molecular system in the form of planar distribution of radially aligned molecular ensemble. This setting gives rise to macroscopic spin-orbit interaction where High Harmonic radiation is emitted while imbued with Orbital Angular Momentum (OAM) whose sign is directly dictated by the helicity of the pump field. We demonstrate this phenomenon in ensembles of $H_2^+$ and $N_2$ molecules with Time-Dependent Density Functional Theory (TDDFT) simulations.

Figures (5)

• Figure 1: A schematic cross-section of a bi-chromatic laser field interacting with a di-atomic molecule, oriented at an angle $\theta$ to the bichromatic field. The inset illustrates the molecular ensemble orientation.
• Figure 2: Harmonic spectra of $H_2^+$ for $\theta=0^\circ$ (as defined in Fig. \ref{['fig: orientation']}) under a bi-chromatic laser field. The ellipticity for each harmonic order is shown above the peaks, the sign of which represents the handedness of the field.
• Figure 3: Normalized amplitude (divided by the maximal value) and phase of the 1$^\mathrm{st}$-5$^\mathrm{th}$ harmonics of $N_2$ subjected to a counter-rotating bi-chromatic laser driving field for LHC (blue) and RHC (red) polarization states.
• Figure 4: Left Panel - Left circular component, Right panel - Right circular component. The upper sub-figures show the Far-field pattern of the 5$^\mathrm{th}$ harmonic under bi-chromatic circularly polarized laser field as achieved from the simulation where the left figure shows the field's phase and the right shows the intensity. The lower sub-figures - show the "reconstructed field" composed of the sum of the first 45 LG modes \ref{['Laguerre-Gauss']} with the calculated coefficients. Both axes are normalized to the harmonic's wavelength.
• Figure 5: Left Panel - Left circular component, Right panel - Right circular component. Decomposition of the far field pattern of the 5$^\mathrm{th}$ harmonic under BCCP laser field into Laguerre-Gaussian modes. The indices of the modes, $p$ and $l$, are arranged along the columns and rows of the image, respectively.