Study On Characteristics Of Acousto-optic Interaction

When light goes through the media with ultrasound, their interaction in media can produce "ultrasonic diffraction", which is similar to raster diffraction. Based on the interaction we can, on the one hand, control the frequency, direction and intensity by ultrasound. On the other hand, we can analyze the signals which transformed by others. According to applications of these two aspects, much more acousto-optic devices have been made for different purposes. Especially, it is in 1960s when laser came into being that devices have been developed greatly both in laser controlling and in signal processing. It reached gradually all areas of military and civilian. To enhance the performance of acousto-optic devices, many countries put much more manpower and resources to research the interaction characteristics of light and sound. Researches are mainly focused on the following four aspects. Firstly, it is to study interaction theory of sound and light. Secondly, it is to develop high-performance materials of them. Thirdly, it is to study the theory and techniques of piezoelectric transducer which would produce ultrasound of lOOMHz or higher. Fourthly, it is to expand the areas of applications of acousto-optic devices.This paper made the following studies both from theoretical and from experimental aspects for characteristics of acousto-optic interaction.(1) From coupling equation which made by light and sound in media, this paper got the interaction rule by analyzing momentum matching and its mismatching. Then characteristics of acousto-optic deflection and modulation are made in acousto-optic normal Bragg diffraction. After the study of 36°Y LN/PM of acousto-optic devices, the curve of deflection and modulation is drawn. The result of experiment coincided with the theory basically. But acousto-optic diffraction efficiency could not reach 100%, which is not coincided with the theoretical result. The author analyzed the reasons in his paper.(2) After analyzed piezoelectric of thickness vibration, the paper provided frequency equation of thickness vibration piezoelectricity. When transducer of thickness vibration is used to acousto-optic devices, frequency characteristics of conductance and transducer consumption are analyzed combined with the diagrams when each platinglayer is the acoustic thin films.The curve of conductance showed that coupling modulus k of piezoelectric layer increased, input conductance also followed when relative impedance remained unchanged. But when choosing different materials hi the media and piezoelectric layer the characteristics of conductance changed obviously. Relative impedance zOm of devices is closed to 1, conductance kept more stable with frequency. But when zOm is far from 1, the conductance changed greatly. The author gets the conclusion that to ensure input conductance keep stably, zOm should approach 1.The curve of consumption showed that this modulus k would affect transducer consumption badly and also affected the bandwidth of transducer. When modulus k is relative smaller, the consumption is smaller too. But the bandwidth was mainly dependent on relative impedance zOm. When zQm a1 the bandwidth is larger. But when zOm is far more larger, it would make a peak in low frequency terminal. The author concluded that when zOm is equal to 1, it was to ensure that transducer has larger frequency bandwidth and its characteristics kept stably.The author analyzed the matching condition between the electrical source and the acousto-optic device. The curve of consumption considering power matching showed that the inner resistance of the electrical source has influence on the bandwidth. No matter what number k or zOm choose, the bandwidth of the transducer reaches the largest when the unitary inner resistance of the power is 1. And in such condition, the power matches the transducer best.(3) On the basis of main index of acousto-optic devices the paper analyzed the design methods of Bragg devices and discussed how to choose the media materials and how to design the sizes. It also explored how to select the bandwidth and frequency of devices. At last the paper made experiment to measure the Bragg bandwidth of LN/PM.