Photorefractive flexoelectric liquid crystal mixtures and their application to laser ultrasonics

A photorefractive effect of mixtures of flexoelectric liquid-crystal (flex LC) was investigated and applied to laser ultrasonics. Mixtures of flex LC, composed of smectic-C liquid crystals, photoconductive chiral compounds, and a sensitizer, are demonstrated to exhibit a large photorefractive effect. The experiments of a two-beam mixing with a photorefractive flexoelectric liquid crystal (PR-flex LC) show that a gain coefficient was measured as 1400 cm–1 and a response time was 960 microseconds, both with an applied electric field of 2.0 V/µm. The large gain and fast response are advantageous for remote ultrasound detection by using two-beam mixing with PR-flex LC. This remote sensing method can be used to probe the internal structure of an object or to measure the thickness of a plate object. The experimental results of acoustic time-of-flight in an aluminum (Al) plate are presented by using an adaptive two-beam interferometer with a PR-flex LC. A 3-D surface topology is shown by using laser ultrasonics with 2-D scanning of a test Al plate. With a fast response time in PR-flex LC, the system is not affected by vibrations in an industrial environment.