Unveiling low THz Dynamics of Liquid Crystals: Identification of Intermolecular Interaction among Intramolecular Modes

Liquid crystal based technologies have found considerably diversified uses and areas of application over the last few decades, proving to be excellent materials for tunable optical elements from visible to near-infrared frequencies. Currently, much effort is devoted to demonstrating their applicability in the far-infrared or THz spectral frequency (1 - 10 THz), where tremendous advances have been achieved in terms of broadband and intense sources. Yet a detailed understanding of the dynamics triggered by THz light in liquid crystals is far from complete. In this work, we perform broadband THz Time Domain Spectroscopy on the low-frequency modes of 4-cyano-4'-alkylbiphenyl (nCB) and 5-phenylcyclohexanes (PCH5) across different mesophases. DFT calculations on isolated molecules capture the majority of the measured response above 3 THz. In particular, the pronounced modes around 4.5 and 5.5 THz mainly originate from in-plane and out-of-plane bending of the cyano group. In contrast, the broad response below 3 THz, linked to modes of the alkyl chain, disagrees with the single molecule calculation. Here, we identify a clear intermolecular character of the response, supported by dimer and trimer calculations.Comment: 14 pages, 4 figure

Towards the epitaxial growth of Au thin films on MgO substrates for plasmonic applications

Surface Plasmon Polaritons (SPPs) in Au thin films are nowadays intensively exploited for sensing applications that leverage the strong optical field confinement at the metal/dielectric interface and the easy functionalization of the Au surface. Moreover, Au thin films represent one of the common starting points for the top-down nanofabrication of plasmonic nanostructures supporting localized resonances. In this framework, strategies for the growth of high-quality Au films on transparent substrates are crucial and not yet fully established. In this study, we exploit MgO(001) substrates for the growth of thin (about 45 nm) Au films, also including an additional buffer layer of Fe. We successfully demonstrate Au samples with reduced roughness and presenting Low-Energy Electron Diffraction (LEED) features, indicating a high degree of crystalline ordering. This is supported by the experimental evidence of an increased (by almost a factor of 3) propagation length compared to a reference Au sample grown on standard glass slides, which is however still significantly lower than the one expected from first principles

All optical sub diffraction multilevel data encoding onto azo polymeric thin films

By exploiting photo-induced reorientation in azo-polymer thin films, we demonstrate all-optical polarization-encoded information storage with a scanning near-field optical microscope. In the writing routine, 5-level bits are created by associating different bit values to different birefringence directions, induced in the polymer after illumination with linearly polarized light. The reading routine is then performed by implementing polarization-modulation techniques on the same near-field microscope, in order to measure the encoded birefringence direction.Comment: 13 pages, 5 figure

Apparatus for vectorial Kerr confocal microscopy

Apparatus for vectorial Kerr confocal microscop