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.
Laser ultrasonics using a photorefractive liquid crystal is investigated with coaxial- and counter-optical setups. The proposed laser ultrasonic method involves irradiating an object with a laser pulse to produce an ultrasonic vibration and then using another laser beam to detect the vibration. The phase of the laser beam reflected from the object is shifted by the ultrasonic vibration. By using liquid crystals with photorefractive properties, this phase shift can be detected. Compared to traditional laser ultrasonic methods, this system offers a simpler optical setup and allows for more precise measurements that are unaffected by environmental vibrations.
Laser ultrasonics using a photorefractive liquid crystal is investigated with coaxial- and counter-optical setups. The proposed laser ultrasonic method involves irradiating an object with a laser pulse to produce an ultrasonic vibration and then using another laser beam to detect the vibration. The phase of the laser beam reflected from the object is shifted by the ultrasonic vibration. By using liquid crystals with photorefractive properties, this phase shift can be detected. Compared to traditional laser ultrasonic methods, this system offers a simpler optical setup and allows for more precise measurements that are unaffected by environmental vibrations.
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