Raman-Nath diffraction by means of thickness-shear oscillating AT-cut quartz crystal resonator

An experiment which uses a plano-convex AT-cut quartz crystal resonator vibrating in 5th overtone thickness-shear mode (the resonant frequency is about 5 MHz) as a Raman-Nath diffraction grating is presented. When a laser beam is passing through the quartz resonator parallel to the thickness-shear-oscillation stress T´₆, the stress creates an optical index variation inside the quartz crystal resonator. The variation functions as a diffraction grating, and the laser beam is diffracted by the Raman-Nath effect. The diffraction angle of output light beams is very small, because the distance between two successive planes of maximum length is large. The diffraction phenomenon is observed only by using a special device. A single mode optical fiber is used as an optical probe. It is scanned in the output diffracted light beams for the measurement of diffracted patterns. The optical probe is able to detect the diffraction light beams as modulated light beams with the resonant frequency of the resonator. When the distance between the top of the probe fiber and the resonator is larger than 10 mm, detected diffraction patterns become fine and clear