Measurement of magnetic birefringence of neon and helium atoms

A high-sensitivity ellipsometer using a GaAlAs diode laser with a 780-nm wavelength was used to experimentally determine the amplitudes of the magnetic birefringence of Ne and He atoms. The measured values of the Cotton-Mouton constant were (1.3/spl plusmn/0.5)/spl times/10/sup -9/ T/sup -2/m/sup -1/ for the Ne atoms and (7.1/spl plusmn/2.5)/spl times/10/sup -10/ T/sup -2/m/sup -1/ for the He atoms under the experimental conditions of 1.5/spl times/10/sup 5/ Pa and 293 K. These amplitudes of the magnetic birefringence provide an absolute standard for detecting the vacuum magnetic birefringence.