Electro-optics and material properties of oblique helicoidal cholesteric tested at oblique incidence of light*

Unique electro-optics of the oblique helicoidal cholesteric (Ch_OH) stem from its heliconical director structure with a pitch and a cone angle that are both dependent on the applied electric field [1]. The field preserves the single harmonic nature of the director modulation and tunes Ch_OH pitch in a broad spectral range as demonstrated previously for the normal incidence of light [2]. In this work, we explore electro-optics of the Ch_OH for an oblique incidence of light. Full pitch periodicity produces first order diffraction with wide bandwidth and total reflection at large angles of the oblique incidence. Diffraction at the half-pitch periodicity shows red and blue shifted spectra for the beams polarized in the plane of incidence and along the perpendicular direction, respectively. The cone angle, as well as other material properties such as off-field cholesteric pitch, a critical field of unwinding the Ch_OH structure, and dispersion of refractive indices are all measured by exploring the diffraction spectra. Unique material properties revealed by the diffraction from the Ch_OH are attractive for applications such as electrically tunable band-pass filters, mirrors, and beam-steering devices. The work is supported by NSF grant ECCS-1906104.