RESUMEN
All-optically controlled beam splitting is demonstrated by a tunable split ratio through polarization modulation. The beam splitters are essentially holographic gratings recorded by means of the interference of two 532 nm beams with asymmetric polarization states in an azobenzene liquid crystal film. It is found that the intensity ratio between zero and the first diffraction order is adjustable through the polarization manipulation of the recording light. An arbitrary split ratio from 0 to 1 is obtained with the photoinduced birefringence of the film being set to an appropriate value, which is independent on the polarization state of the probe light. Furthermore, the formation processes of the recorded beam splitters are contributed to the dual-grating coupling, and the tunable split ratio under various polarization conditions is discussed in terms of the Fresnel theory and Jones matrices.
RESUMEN
Polarization modulation was achieved by means of a new type of grating recorded with two 532 nm beams at varying polarization angles in an azobenzene side-chain liquid-crystalline polymer film through light regulation instead of voltage control. In contrast to conventional polarization holographic gratings, the polarization state of the ± first-order diffracted beams of the recorded gratings depended strongly on angles between polarization directions of two recording beams, while the polarization state of the second-order diffraction remained unchanged. With the polarization angle changing from 0 to 90 deg, the ± first-order diffraction efficiency increased from 5.15% to 10.53%. Diffraction properties of the recorded gratings were attributed to the combination of polarization holographic gratings and amplitude gratings based on the calculation of Jones matrices and polarization holographic theory.
RESUMEN
RNA is a pivotal molecule that plays critical roles in various cellular processes. Quantifying RNA structures and interactions is essential to understanding RNA function and developing RNA-based therapeutics. Using a unified five-bead model and a non-redundant database, this paper investigates the structural features and interactions of five commonly occurring RNA motifs, i.e., double-stranded helices, hairpin loops, internal/bulge loops, multi-branched junctions, and single-stranded terminal tails. Analyzing detailed distributions of RNA local structural features and base-base interactions reveals a preference for helical structures in both local backbone structures and base orientations. The interactions between adjacent bases exhibit motif-specific and sequence-dependent characteristics, reflecting the distinct topological constraints imposed by different loop-helix connection modes and the varying pairing and stacking interactions among different sequences. These findings shed light on the stability of RNA helices, emphasizing their significance in providing dominant base pairing and stacking interactions for RNA structures and stability. The four non-helix motifs encompass unpaired nucleotide loops and exhibit diverse base-base interactions, contributing to the structural diversity observed in RNA. Overall, the complexity of RNA structure arises from the intricate interplay of base-base interactions.