The photorefractive effect of smectic liquid crystal mixtures was investigated and the application to laser ultrasonic measurements was demonstrated. Smectic liquid crystal mixtures, composed of smectic-C liquid crystals, photoconductive chiral compounds, and a sensitizer, exhibit a fast photorefractive effect. The principle of ultrasonic measurement is that a nanosecond laser pulse is shot on an object to cause an ultrasonic vibration, a continuous laser beam is irradiated on the object, and the ultrasonic variation is detected using photorefractive two-beam coupling. This method can investigate an object's thickness and internal structure without contact.

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Takeo Sasaki, Toshinobu Takashi, Gouta Ikeda, Junko Watanabe, Miku Nagaoka, Shinnosuke Yamazaki, Yumiko Naka, and Khoa Van Le, "Laser ultrasonics for measurement of the thickness of metal plates using a photorefractive liquid crystal," Proc. SPIE 12574, Holography: Advances and Modern Trends VIII, 1257408 (Presented at SPIE Optics + Optoelectronics: April 25, 2023; Published: 31 May 2023); https://doi.org/10.1117/12.2664898.