Observation of photorefractive effects in blue-phase liquid crystal containing fullerene-C₆₀

Photorefractive effects manifested in two beam coupling and side diffractions are observed in fullerene-C₆₀ doped blue-phase liquid crystals (BPLC - C₆₀) upon application of a DC bias field. The mechanism at work here is attributed to BPLC lattice distortion by the combined DC (E_dc) + photorefractive space-charge (E_photo) fields, in addition to the DC + optical field induced effects reported in previous studies of dye-doped system. The first order diffraction efficiency of ∼2 × 10^-3 and beam coupling gain of over 2% are observed in a 55 μm thick sample with input laser beam power of 5 mW at an applied DC voltage of 160 V. The effective nonlinear index coefficient n₂ of BPLC - C₆₀ is measured to be on the order of 10^-2 cm²/W, which is slightly lower than their NLC counterparts. Owing to the isotropy of BPLC optical properties, these effects can be observed with more relaxed requirements on the laser polarizations, directions of incidence, and sample orientations.