法-珀干涉绝对距离测量中的声光移频器双通道配置方法

Method on double-pass acousto-optic frequency shifter in absolute distance measurement using Fabry-Perot interferometry

为在能量天平动圈位移测量中实现大范围纳米精度法-珀干涉绝对距离测量,提出了声光移频器双通道配置,实现了调谐范围为200 MHz的可调谐频差.通过分析声光移频器调制带宽与衍射效率的平衡与入射光束聚焦透镜的关系,确定透镜的最佳焦距范围;利用零级光斑分布特点准确定位入射光束,保证一级衍射光束质量.声光移频器在调制带宽内的实验单通道和双通道峰值衍射效率分别为79.54%,61.41%;声光移频器双通道配置输出的一级衍射光束与入射本征光束的拍频范围为440—640 MHz,是单通道调制带宽输出220—320 MHz的两倍,信噪比好.理论分析表明,声光移频器双通道配置方法实现的可调谐频差可测量腔长变化范围约为53 mm的折叠法-珀腔.

In order to realize nanometer-scale absolute distance measurements based on Fabry-P6rot interferometry for long-range displace- ment measurement of the moving coil in Joule balance, the acousto-optic frequency shifter （AOFS） in double-pass configuration is presented, and a tunable frequency difference in a range of 200 MHz is achieved. The focus length of the lens is determined by ana- lyzing the relationship of the tradeoff between the AOFS modulation bandwidth and its diffraction efficiencies; the beam spot of the first-order diffraction beam is guaranteed by accurately positioning the focused beam according to the distribution of the zero-order diffraction beam spot. The experimental single-pass and double-pass peak diffraction efficiency of the AOFS are 79.54% and 61.41%, respectively; the tunable frequency difference of 440--4540 MHz, which is twice the single-pass modulation bandwidth output of 220---320 MHz, is obtained by the beat note between the incident beam and the first-order diffraction beam of the double-pass AOFS, and has a good signal-to-noise ratio. Theoretical analysis shows that a folded Fabry-P6rot cavity length displacement of about 53 mm can be measured through the tunable frequency difference achieved by means of double-pass AOFS.