An integrating sphere of simple construction has been developed for the ir. It has a high efficiency that is not materially affected by aging processes. Experimental measurements of the relative efficiency of this sphere have been made for the wavelength range from 1 µ to 2.6 µ. These data agree with theoretical predictions. It was also predicted that the efficiency of the sphere would increase from 2 µ through to the millimeter wavelength range. The measurements show the ir sphere to have a higher efficiency (2.5 times higher at 2.6 µ) than the conventional MgO-coated integrating sphere.
James C. Morris, "Integrating Sphere for the Infrared," Appl. Opt. 5, 1035-1037 (1966)