- Measurement principle
When glass plates are bonded or fused together to form a cell, stress is applied to the joint area, and birefringence is induced by the photoelastic effect. The cell must be sufficiently free from birefringence to be used in the measurement of prisms. Here we show an example of measuring the birefringence of a cell made of Pyrex glass, as shown in the figure below. The cell is fused with a low-melting glass. Because the thermal expansion coefficient of the Pyrex glass differs from that of the low-melting glass, stress is generated in the glass during the cooling process after fusion, resulting in birefringence.
The measurement results are shown in the figure below.