Measurement of the Cotton–Mouton constants of noble atoms

Magnetically induced birefringence (the Cotton–Mouton effect) of argon, neon, and helium atoms was measured with a high-sensitivity ellipsometer with a 790-nm GaAlAs diode laser. The detection limit of the change in ellipticity was attained to a shot-noise-limited value of 10-10 rad. We determined the absolute values of the ellipticity changes caused by noble atoms using the light extinction ratio of the ellipsometer as an absolute standard, with this ratio measured by a method based on Malus’s law. The measured values of the Cotton–Mouton constant were (7.1±2.5)×10-10 T-2 m-1 for He atoms, (1.3±0.5)×10-9 T-2 m-1 for Ne atoms, and (1.1±0.2)×10-8 T-2 m-1 for Ar atoms at a gas pressure of 1.52×105 Pa and a gas temperature of 285–293 K.