Research On Wavefront Distortion In Inter-Satellite Laser Interferometer

The inter-satellite laser interferometer plays an important role in space gravitational waves detection programs such as LISA,Tianqin,and Taiji.It is used to measure the distance variations of the arm length,on the level of hundreds of thousands to millions kilometers,between two satellites.The resolution of displacement measurement needs to reach the picometer level.It extracts the change of the arm length difference of the interferometer caused by the gravitational waves,and extracts the gravitational wave signal from the phase of the interference signal,so it has extremely high requirements for the phase noise of the interference signal.The wavefront distortion in the laser will not only affect the intensity of the received beam,but also couple with the jitter of the transmitted beam in satellite,which will increase the phase noise of the measurement signal and reduce the signal-to-noise ratio of the signal.Therefore,the wavefront distortion in laser beam must be measured and suppressed.This paper investigates the influence of wavefront distortion internal inter-satellite laser interferometer on the interferometer and interference signal,and the wavefront distortion compensation technology,to reduce the influence of wavefront distortion on the interference signal,which is beneficial to the "Tianqin" project.The processing and assembly of optical components,the structure of the optical path,and the influence of solar radiation on the telescope system inevitably introduce wavefront distortion.Therefore,the control of the wavefront distortion of the optical system in the satellite has become an important content.The control algorithm and feedback control method for the number of hundreds of thousands of control units in the wavefront corrector is a difficult part.We studied the influence of wavefront distortion on heterodyne laser interferometer,and used adaptive optics to control the wavefront distortion of the heterodyne laser interferometers.We measured the wavefront distortion caused by the optical components and optical path structure,used the spatial light modulator as the wavefront corrector,and used the Zernike mode method to fit the wavefront.We adopt the phase conjugation method eliminates wavefront distortion,and apply proportional-integral feedback control method to compensate the wavefront difference between the received signal light and the reference beam,meanwhile,we developed a set of adaptive optics real-time wavefront distortion compensation system.Finally,the root mean square value of the wavefront distortion in the interferometer was reduced to 0.046λ within 10 hours,the standard deviation at stability was 0.003λ.It effectively eliminates the influence of wavefront distortion on the interferometer,and provides a practical reference for optical design,error distribution,and noise sources in satellites.