Preliminary Investigation of the Vacuum Magnetooptic Effect : Evaluation of the Non-Resonant Magnetooptic Birefringence due to Low-Density Residual Gases

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In a preliminary investigation of the vacuum magnetooptic effect, we evaluated the effect of non-resonant magnetooptic birefringence due to residual gases contained in the vacuum cell. We measured the magnetooptic birefringence coefficient of the gas under the atmospheric pressure. We used a semiconductor laser oscillating at 780 nm as a light source. The laser output flux was stabilized to 2X10^<-4>. The extinction ratio of the polarization analyzer was (2-3)X10^<-8>.Light from the laser was passed through a linear polarizer and a retarding plate to convert the light beam into an elliptically polarized state. We passed the light bean through a cell containing oxygen molecular gas, which was placed in magnetic field of 0.8T.The field was oriented at 45 degrees from the polarization azimuth of incident light and was transverse to the optical path. The polarization change caused by magnetically induced optical anisotropy of oxygen gas was detected with a polarization analyzer.The measured magnetooptic birefringence of oxygen molecule is expressed by DELTAn=ClambdaB^2, with C=-(5.4(〕SY.+-.〔)0.5)x10^<-15>[G^<-2>cm^<-1>](lambda=780nm, 16ﾟC, 1 atm.). The constant C for nitrogen and argon is smaller than that fo oxygen. The magnetooptic birefringence of residual gases at pressures above 10^<-10>[Torr] can affect the detection of the vacuum birefringence induced by a magnetic field.