Measurement of the Optical Path Difference Caused by Steering Mirror Using an Equal-Arm Heterodyne Interferometer  
[PERSON]  
1 Key Laboratory of Space Active Opto-Electronics Technology, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200803, China; [EMAIL_ADDRESS] (W.Z. );  
[EMAIL_ADDRESS] (Q.J. ); [EMAIL_ADDRESS] (X.W. ); [EMAIL_ADDRESS] (Y.X)  
[PERSON]  
3 Taiji Laboratory for Gravitational Wave Universe, School of Physics and Optoelectronic Engineering, Hangzhou Institute for Advanced Study, Hangzhou 310012, China; [EMAIL_ADDRESS] (Y.G. ); [EMAIL_ADDRESS] (X.Q.) [PERSON]  
1 Key Laboratory of Space Active Opto-Electronics Technology, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200803, China; [EMAIL_ADDRESS] (W.Z. );  
[EMAIL_ADDRESS] (Q.J. ); [EMAIL_ADDRESS] (X.W. ); [EMAIL_ADDRESS] (Y.X)  
[PERSON]  
1 Key Laboratory of Space Active Opto-Electronics Technology, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200803, China; [EMAIL_ADDRESS] (W.Z. );  
[EMAIL_ADDRESS] (Q.J. ); [EMAIL_ADDRESS] (X.W. ); [EMAIL_ADDRESS] (Y.X)  
[PERSON]  
3 Taiji Laboratory for Gravitational Wave Universe, School of Physics and Optoelectronic Engineering, Hangzhou Institute for Advanced Study, Hangzhou 310012, China; [EMAIL_ADDRESS] (Y.G. ); [EMAIL_ADDRESS] (X.Q.) [PERSON]  
1 Key Laboratory of Space Active Opto-Electronics Technology, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200803, China; [EMAIL_ADDRESS] (W.Z. );  
[EMAIL_ADDRESS] (Q.J. ); [EMAIL_ADDRESS] (X. Research on heterodyne laser interferometers has always been a hot topic. The main research contents of heterodyne interferometers with different design configurations are also different. To avoid interference caused by excessively long interference arms, interferometers are generally designed to be relatively compact. For example, they can take the form of a heterodyne interferometer in a single, small, two-dimensional cubic optical unit [6]. Another approach involves abandoning spatial light and using optical fibers to design interferometers for studying repeated positioning accuracy [7]. A heterodyne interferometer designed using the grating diffraction effect and high-angular-sensitivity total internal reflection was used to detect small wavelength shifts [8]. To study the linearity and phase noise contributions of the interference phase readout, the interferometer was designed in a hexagonal quasi-monolithic optical bench style [9]. Aluminum optical benches are the most common style of laboratory interferometers due to their relative simplicity. They have been used to study methods of measuring amplitude enhancement [10], measuring piezoelectric-drive displacement accuracy [11], measuring straightness and displacement error simultaneously [12], laser linewidth measurement [13], and straightness measurement of linear motion platforms [14]. Studying the noise in each part of the interferometer and eliminating it through data post-processing can greatly improve the measurement accuracy of the interferometer. Laser frequency noise [15; 16], laser Relative Intensity Noise (RIN) [17; 18], temperature fluctuations [16; 19], electronic readout noise [19], optical components [15], geometric TTL noise [20], etc., have an impact on the measurement accuracy of the interferometer. Here, laser frequency noise is reflected in the optical path through the differential of the interferometer arms. After the above-mentioned noise is identified in principle [6] and its model is estimated [14], some non-periodic errors [12] and non-linear errors [16] can be eliminated through data post-processing. However, there is currently no research on measuring the optical path difference (OPD) caused by a steering mirror using laser heterodyne interferometry. This paper designs a strictly equal-arm laser heterodyne interferometer to measure the OPD caused by the steering mirror.