Photoelectric intensity ratio meter as receiver for the phase contrast refractometer

The phase contrast refractometer converts optical phase differences into intensity differences, and thus the receiver is a photometer. The present design is photoelectric with one phototube and a grey wedge, an electronic device acting as a null indicator. The ratio between the intensities of the two areas to be measured is accurate to 0.3%, corresponding to a difference in optical path in the phase object of 0.0004 λ.