検査・光学
Polariscope Test
Japanese: 偏光板測定
An inspection method in which light is transmitted through glass sandwiched between two polarizing filters, visualizing residual stress (retardation) as interference colors.
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The polariscope test is an inspection method in which white light is passed through a glass specimen placed between two orthogonal linear polarizers (and a λ/4 waveplate, if necessary), thereby visualizing the residual stress within the glass as interference colors (interference of light caused by birefringence). This method utilizes the phenomenon of photoelasticity, in which the refractive index of glass changes depending on the magnitude and direction of stress. Measurement protocols compliant with standards such as ASTM F218 are available.
A simple setup suitable for hobbyists can be constructed for about 15,000 yen using two linear polarizing sheets (such as Edmund Optics #43-783) and an A5-sized white LED light panel. Rei Chikaoka (2012, p. 95) also includes a photograph of this simple setup used as a distortion test plate. The Bullseye recommended criterion is 10 nm/cm or less (5 nm/cm or less for storage quality); the higher the retardation value, the higher the residual stress, and the greater the risk of long-term damage. Strain checks using polarizer measurements are also performed on thick OYF substrates, and stress values within the acceptable range have been confirmed even after annealing times shorter than those predicted by theoretical calculations.
Related Concepts
Together with photoelasticity, retardation, and the Michel-Lévy chart, gain a systematic understanding of polarizer measurements, from their underlying principles to the practical procedures.
This entry is written in Japanese by Rei Chikaoka and translated for readers outside Japan. If something reads oddly, the original is the source of truth.