Acousto-optic Interaction Research Of Produce Beat Frequency

Since the 30’s of last century, the acousto-optic interaction has been studied, but was not paid enough attention due to the small diffraction grating of ultrasonic frequency shift and the deflection angle. The theory of acousto-optic interaction was development quickly after the appearing of the laser, and devices, based on the theory of acousto-optic interaction, was applied to many fields. With perfecting of the acousto-optic theory, the mature technique of acousto-optic devices and high performance of acousto-optic materials appear continuously, the Acoustic-optical is in constantly progress and perfect.When the acousto-optic medium acrossed by ultrasound, the refractive index of the medium will be affected of the strain modulation and changes periodically, and the media will evolves into a "raster". when the laser acrossed by this acousto-optic medium, it will be diffracted. The main works of mine paper are as follows:Firstly, progresses, trends and application in various fields of theoretical research of the acoustic optic technology were introduced.Secondly, the optical beat frequency and light interference were compared,explains their similarities and differences. Optical beat frequency is a form of exercise intensity changes with time phase, and the interference of light is one of the forms of exercise intensity changes with the change of optical path difference. Working principle of acousto-optic devices was described, and two kinds of diffraction based on different Q values were introduced,including Raman- Nath diffraction and Prague diffraction.By analyzing the internal structure of the acousto-optic, the reason why the laser beam would be diffracted through the acousto-optic devices is explained. The refractive index of the medium would be effected by ultrasonic, then the refractive index of the medium changed periodically, just like a movement of the grating, so the light wave would be modulated byacoustic field when it gets into the medium, and the frequency of the diffraction point became difference due to the existence of the doppler frequency shifted. The theoretical analysis indicates that the ultrasonic waves were difference in the different case in the medium, they could be traveling wave or standing wave. By analyzing the frequency spectrum of incident light,the modulation frequency and acoustic frequency would be changed after the light is modulated, the ultrasonic traveling wave field and the ultrasonic standing wave which traveled in the acoustic-optic medium could be distinguished.Finally, by the theory of the acousto-optic interaction and using high frequency deterctor, confocal scanning interferometer and a spectrum analyzer, the beat frequency phenomenon of Raman-Nath diffraction point was displayed visually, and its produce mechanism was analyzed, and the rules of formation of beat frequency were summarized, and its generation condition was explored.