Tuneable ferroelectric liquid crystal microlaser

Abstract

We demonstrate electric field tuning of Whispering Gallery Mode resonances in microdroplets of a dye-doped ferroelectric liquid crystal suspended in highly transparent fluorinated polymer solution CYTOP. The ferroelectric liquid crystal is a 9:1 mixture of CE3 and CE14 ferroelectric liquid crystals, exhibiting the ferroelectric Sm C* phase between 42°C and 74°C with a rather short helical pitch of 300 to 500 nm. In the Sm C* phase, the droplets show excellent optical homogeneity with perpendicular anchoring of liquid crystal molecules at the surface. Upon the excitation with a pulsed laser, the ferroelectric liquid crystal microdroplets emit laser light showing multimode WGM spectrum. When an external slowly varying electric field is applied along the direction of the excitation laser beam, we observe a red-shift of the WGM resonances, indicating an effective increase of the optical path for WGM resonant light. The shift is fully reversible, it is quadratic in the applied electric field and has a value of ∼ 4.5 nm at an electric field of 2 V(μm)−1. It is qualitatively explained by considering the soliton-like deformation of the helical ferroelectric Sm C* structure in an external electric field.