Used Of Co <sub> 2 </ Sub> Laser Heterodyne Detection Of The Acousto-optic Frequency Shifter Device Research

Based on the acousto-optic interaction principle and multiple plane-wave scattering theory, the mathematical model of acousto-optic frequency shifter (AOFS) is built to determine its parameters. Through systematically studying on the bulk-wave high-frequency far-infrared acousto-optic frequency shifter (AOFS), especially on the application characteristics of high-frequency far-infrared acousto-optic devices in high power laser, some temperature-controlled methods, such as back endothermic structures and surround-based water cooling structures, are used to remove heat instantly to keep the internal temperature of acousto-optic devices uniform and eliminate the temperature gradient. With these methods, the diffractive efficiency can be increased 10% and the spot quality is improved greatly.This dissertation introduces the whole design and fabrication procedure of the acousto-optic frequency shifter and presents detail descriptions on the mono-crystal germanium acousto-optic interaction materials, LiNbO3 transducer, and cold-indium vacuum pressure welding process. Based on analyzing modification mechanism of mono-crystal germanium, innovation study on the materials or processes about the fine selection of mono-crystal germanium, electroplating electrode and welding electrode wire is carried out and the middle and far-IR acousto-optic devices with high diffractive efficiency and high reliability is developed successfully.The design method of the matching-circuit network for acousto-optic frequency shifter is also described in detail and the optimal matching network between transducer and acousto-optic interaction material of middle far-IR AOFS is obtained.In this dissertation, the experimental parameters (such as diffractive efficiency, extinction-ratio, optical transmittance, etc) for test devices are determined and test scheme for the correlation of the AOFS frequency shift and ultrasonic frequency is presented. When the input power is over 15W and the driving frequency is stable, the internal temperature of the AOFS rises obviously, and as a result the thermostatically controlled condition the spot quality is poor and the diffractive efficiency begin to deteriorate.The potential application of AOFS in laser heterodyne coherent detection, coherent-detection-based laser radar, particle collision velocity analyzer is discussed briefly.