Stress Measurement

Stress in optical materials commonly presents itself by generating an anisotropy in the material (Stress-Induced birefringence).  Measuring the birefringence, material thickness, and knowing the material’s stress optic coefficient, allows the calculation of the resulting differential stress in the material.  Stress in these types of materials may be permanently present resulting from stress created during the manufacturing process, such as with injection molded plastics or in polished optical materials or may be temporarily induced by applying a force to a material such as occurs in Hinds Photoelastic modulator (PEM) optical assemblies.

Stress-induced birefringence can be measured the same way other low-level birefringence is measured.  Hinds Instruments manufactures the award winning Exicor® instrumentation for the accurate and precise measurement of birefringence and stress induced birefringence.


Quality control for:

– Plastics

– Flat panel display glass

– Optics

– Silicon for solar cells


Exicor® Birefringence Measurement Systems


J. C. Kemp, Basic Laboratory set-up for various measurements possible with the photoelastic modulator, Application note, Hinds Instruments, Inc. (1975)

J. Schellman and H. P. Jensen, “Optical Spectroscopy of Oriented Molecules,” Chem. Rev. 87, 1359-1399 (1987)

S. J. Johnson, “Simultaneous dichroism and birefringence measurements of sheared colloidal suspension in polymeric liquids,” Ph. D thesis, Stanford Univ. (1985).

T. C. Oakberg, “Measurement of Low-level Strain Birefringence in Optical Elements Using a Photoelastic Modulator,” SPIE, 2873, 17-20 (1996)

Residual Stress Birefringence white paper

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