A fiber-coupled infrared laser heterodyne interferometer system based on optical scanning is proposed. In this system, the sample is scanned through the combined configuration of a micro-electro-mechanical system mirror and an F-theta lens set. The distortion index of the F-theta lens set is less than 0.01%. In order to enhance the sensitivity of the heterodyne detection system, the dual-balanced heterodyne detection is applied in the measurement of the intermediate frequency signal. The theoretical model and the signal-to-noise ratio expression of the dual-balanced heterodyne detection system are derived in this paper. The interferometer system has a vertical resolution of 0.43 nm and a lateral resolution of . The stability of this system is approximately 1.90 nm for 1 h. Furthermore, the system possesses 8 s measurement time, 94.18 MHz output frequency, and 1550 nm eye-safe operating wavelength. Application of the system may be realized for any sample that has higher transmittance for the eye-safe wavelength.
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