| 摘要 |
PURPOSE:To obtain the titled lens, safely and readily by bringing a medium containing silver ions into contact with the surface of a plate phosphate glass material, and diffusing and introducing the silver ions thereinto by the ion exchange to form a refractive index distribution in the thickness direction of the flat glass. CONSTITUTION:A medium containing silver ions, e.g. a mixed molten salt of silver nitrate and potassium nitrate, is brought into contact with at least one side of a plate phosphate glass material, and the silver ions are diffued and introduced into the flat glass by ion exchange and form the concentration distribution of the silver ions. Thus, the refractive index gradient is formed in the thickness direction from the surface to the interior thereof. The part having the desired refractive index distribution is then cut out of the flat glass and the direction of the refractive index gradient is made in agreement with the optical axis to carry out grinding. Thus, the aimed lens having a great refractive index in the axial direction can be readily produced without using a diffusing cation having strong toxicity, e.g. thallium.
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