A phase-contrast refractometer for measurements in the infrared has been constructed. The optical and mechanical arrangement is discussed and a brief description of the experimental procedure is given. A value for (<i>n</i>-1) of air of 0.00026834 was obtained for the 1.014-µ line of mercury. The standard deviation of the mean is ±0.7%.
W. S. RODNEY and E. DJURLE, "Infrared Phase-Contrast Refractometer," J. Opt. Soc. Am. 48, 388-389 (1958)