Tunable broad-temperature-range grating based on the liquid crystal flexoelectric effect and its spectral scanning: Forming one-dimensional, two-dimensional, and annular diffraction patterns at different orientations

Bent-core nematic (BCN) liquid crystals (LCs) can form a variety of grating structures under different orientations and exhibit exceptional optical tunability due to their unique flexoelectric effect. Here, we develop a flexoelectric nematic LC (NLC) mixture with broad temperature range (0--65 \ifmmode^\circ\else\textdegree\fi{}C). Based on this material system, we investigate the grating structure formed by the flexoelectric NLCs under different orientations (planar, vertical, and annular photoalignment) and analyze their responses to voltage and temperature. As a result, we achieve one-dimensional, two-dimensional, and annular diffraction patterns with tunable periodicity. Notably, under an external field, we observed the microdomain multidomain phenomenon of NLC gratings in the vertical cell: numerous micrometer-scale segmented gratings spontaneously align in different directions while maintaining a uniform periodicity. This isotropic grating array exhibits an anomalous annular diffraction pattern under laser irradiation: whereas an individual segmented grating produces directional diffraction, the statistically uniform distribution of segmented gratings results in the superposition of diffracted intensities in multiple directions, ultimately forming concentric annular patterns with tunable radius. This tunable diffraction angle grating, applied to spectral scanning, is simple to prepare, low-cost, and can complete a visible light scan in 1.25 s, providing new possibilities for the development of miniaturized spectrometers.