Acousto-optic laser chopper based on light diffraction by hypersonic standing waves in lithium niobate single crystal

The paper presents results on the theoretical and experimental investigations of an acousto-optic modulator based on single crystal lithium niobate. The modulator uses a regime of operation with a standing longitudinal acoustic wave generated in the material along the axis X. The optimum cut in the LiNbO3 crystal has been calculated and it is shown that the highest figure of merit can be obtained in the YZ-plane of the crystal if light propagates not along the crystalline axis Z or Y but at an angle of 37° with respect to the axis Y. Application to the instrument of a harmonic driving electric signal at a frequency included in the range 450–550 MHz resulted in modulation of light intensity and generation of a sequence of laser pulses having repetition frequencies 0.9–1.1 GHz. The efficiency of light diffraction in the examined laser chopper was equal to 7–10% depending on frequency and power at a driving electric power of 1.0 W or higher and a wavelength of light equal to 532 nm. The possibilities to develop a similar acousto-optic modulator but with repetition frequencies up to 10 GHz are discussed.

► Found an optimal cut of a lithium niobate crystal promising for application in a fast laser acousto-optic modulator.
► Calculated basic parameters of the modulator generating a sequence of short laser pulses with repetition frequencies in the gigahertz region.
► Designed and fabricated the acousto-optic modulator on the base of a lithium niobate crystal and tested operation of the device by means of laser radiation at an optical wavelength of 532 nm.
► Demonstrated a chopper regime of the modulator operation with a repetition frequency of optical pulses equal to 0.9–1.1 GHz and a diffraction efficiency of 7–10%.
► Revealed the influence of acoustic attenuation in the lithium niobate crystal on the magnitude of maximal repetition frequency in the modulator.