Long-lived stationary holographic gratings and optical memory in ferroelectric nematic liquid crystals

Stable stationary holographic gratings were recorded in a pure, room-temperature ferroelectric nematic liquid crystal (NFLC) using degenerate two-wave mixing. These structures exhibit extraordinary six-month stability and resist erasure under the electric-field and thermal-cycling conditions investigated, indicating a persistent material modification rather than reversible reorientation. Polarization-dependent readout reveals nearly constant diffraction efficiency despite strongly anisotropic transmission of the host medium, indicating both phase and amplitude contributions to the optical response. Applied AC fields enable reversible, frequency-dependent modulation of diffracted intensity governed by slow dipolar dynamics. These findings establish NFLCs as a robust, non-volatile platform for electrically tuneable photonic devices, bridging the gap between fast dynamic holography and permanent optical memory.