Optics: measuring and testing – Material strain analysis – With polarized light
Patent
1975-03-06
1976-07-13
Stern, Ronald J.
Optics: measuring and testing
Material strain analysis
With polarized light
356114, G01B 1116
Patent
active
039690237
ABSTRACT:
A glass ophthalmic lens which has been strengthened by thermal tempering or ion exchange treatment has increased impact resistance and durability, but such strengthening does not alter the appearance of the lens sufficiently to render the presence or absence of strengthening visually ascertainable even by one of high skill. It being necessary to inspect for the presence or absence of strengthening prior to dispensing lenses to the public, the present invention contemplates immersion of the lenses in a transparent liquid of approximately the same refractive index as the material of the lenses and projection of linearly polarized light through the fluid and lens. Viewing of the thus illuminated lens through a light polarizing analyzer reveals readily observable stress patterns in strengthened lenses and a lack of such patterns in non-strengthened lenses.
REFERENCES:
patent: 2375399 (1945-05-01), Wittig
patent: 2388352 (1945-11-01), Vent
patent: 2869417 (1959-01-01), Allen
patent: 3052153 (1962-09-01), Powell
patent: 3589812 (1971-06-01), Malakoff et al.
patent: 3815997 (1974-06-01), Alaska
Brandt Neill M.
Deeg Emil W.
American Optical Corporation
Berkenstock, Jr. H. R.
Nealon William C.
Punter Wm. H.
Stern Ronald J.
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