Optical materials are an important part of optical instruments and the objects of optical parts processing. Optical materials include optical glass, optical crystals, and optical plastics. The following introduces the basic knowledge of optical glass:
Composition of optical glass
The main difference between optical glass and ordinary glass: optical glass has high transparency, high physical and chemical uniformity, and specific and precise optical constants. Optical glass contains most of the elements in the periodic table, but the composition and content are different.
Generally, the main component of optical glass is silica, also known as quartz sand. When smelting glass, other substances must be added to improve the performance of the glass and meet the needs of system imaging. For example, the addition of Al2O3 can improve the chemical stability and mechanical strength of the glass; the addition of lead oxide and barium oxide can increase the refractive index of the glass, but the chemical stability is reduced; the addition of sodium oxide can reduce the melting temperature; in addition, other types of oxidation can be added as needed Things.
The glass with silicon dioxide SiO2 as the main component belongs to silicate glass, the glass with diboron trioxide B2O3 as the main component belongs to borosilicate glass, and the glass with phosphorus pentoxide P2O5 as the main component belongs to phosphate glass.
Physical properties of optical glass
Glass form
Glass is not strictly solid. The glass smelt does not have a certain solidification temperature during the cooling process. The glass retains the structure of liquid molecules in an irregular arrangement, that is, the low-temperature solid retains the high-temperature liquid amorphous structure, which is called the glass state. The physical properties of glass
Isotropy: The properties of glass, such as hardness, elastic modulus, and refractive index, have the same values measured in all directions.
Metastable state: the process of glass transition from a molten state to solid state is continuous and reversible.
Classification and naming of optical glass
There are many types of optical glass, most of which are colorless optical glass. The name of optical glass mainly refers to colorless optical glass.
Varieties and grades of optical glass: Each country and each glass manufacturer has its own variety classification and designation method, most of which use Latin letters as the variety mark, such as K, ZF, F, etc. The variety is followed by the brand mark (my country’s national standard Arabic numerals indicate serial numbers).
According to the classification method of various countries, optical glass is divided into two categories: crown glass and flint glass according to the size of the Abbe coefficient. The approximate dividing line is γ=50; in China, K represents crown glass and F represents flint glass.
Under the crown and flint glass, other sub-categories are derived based on the refractive index and chemical composition.
Colorless optical glass classification
According to the position of the refractive index nd and the dispersion coefficient vd in the nd-vd field map and the glass composition.
Optical glass grades
Each optical glass grade is composed of the code number plus the serial number of the glass category name to which it belongs. In addition, six numerical values are used as codes to characterize each grade. The first three digits represent the three digits after the decimal point of the refractive index of the glass, and the last three digits represent the Abbe number of the glass.
For example: H-K9L, nd=1.51680, vd=64.20, the code is: 517642
Lead, arsenic, cadmium-free glass grades:
Glass grades free of lead, arsenic, cadmium and other radioactive elements are indicated by “H” plus “-” as a prefix, such as H-K9L.