The Study Of An Autocollimator With Nanoradian Resolution Used In The Precise Torsion Balance

The torsion pendulum is a high-sensitivity tool for detecting weak force,it has been widely used in the gravitational experiments.In general,measuring the deflection of the pendulum precisely is an important factor to ensure the accuracy of the torsion balance.As a high-accuracy detector of small angle,the autocollimator is often used to monitor the motion of the pendulum.As for our current situation,the angular detection noise is the major limitation of the torsion noise in the high frequency.In order to further advance the measurement accuracy of the torsion balance,we developed an autocollimator with the 1 nrad resolution.Firstly,the parameters of the autocollimator were determined through analyzing the expression of resolution.The reticule with multi-slit structure was used to reduce the random noise.Linear CCD was selected to match the multi-slit reticule.And the aberration of the edge slit could meet the system requirements after used doublet lens.Then analyzed the influence caused by the object plane and the image plane outof-focus.The result showed that when the image plane was out-of-focus,the result of angle measurement was related to the position of the target mirror.For a 500-millimeter-focal-length autocollimator,it would introduce angular deviation when the image plane was 0.1 millimeters away from the focal plane.It must control the location of the image plane with the autocollimator strictly.The various noises of the autocollimator have been studied.Two modulation experiments were performed to study the influence for the resolution caused by the intensity that CCD received.The refractive model of air was established to analyze the variation of the resolution with the temperature.The common-mode noise has been removed by using common-path method.After fully eliminated the various noises of the system,the autocollimator could 0.2%achieve a resolution of 0.008 ?rad/(?) from 10 mHz to 100 mHz.