Optical Engineering / Apps / Glass Catalog

Multiple filters can be applied on the glass catalog to restrict the glass selection process. These can be found in the filters tab and are divided into different categories including cost, transmission boundaries, thermal and mechanical properties, environmental resistances and miscellaneous features like lead content, radiation resistance etc.

Glasses can be restricted by their relative cost to N-BK7 glass, which is considered as the default glass by suppliers. If a relative cost is supplied and none if known for a given glass, it is automatically removed from the glass selection.

Glasses can be restricted by their transmission by specifying:

• a minimum wavelength such that the glass has a transmission of at least the given threshold over a path of 1 cm at that wavelength;
• a maximum wavelength such that the glass still has transmission of the given threshold over a path of 1 cm at that wavelength;
• a transmission threshold to use.

Glasses can be restricted by their thermal properties by specifying:

• a minimum coefficient of thermal expansion (CTE) given in ppm/°C. Glasses with high CTE are more difficult to grind but also more susceptible of failure in highly-fluctuating temperature environments;
• a maximum thermal stress factor which gives how much maximum stress the glass can suffer from a given thermal load. This is a refinement over the CTE selection and has to be considered as the worst-case scenario when the glass does not have the time to conduct heat, such as in thermal shocks;
• a minimum heat conductivity for the glass to favor glasses that will dissipate heat more quickly and are therefore less susceptible to thermal shocks;
• maximum birefringence and refractive index change for a given thermal load. Again, this has to be considered as the worst case scenario where the glass does not have time to conduct heat.

Glasses can be restricted by their mechanical properties by specifying:

• maximum birefringence and refractive index for a given stress.

Glasses can be restricted by their resistance to environmental factors including:

• resistance to strongly alkaline solutions defined as the time required to remove a 100 µm layer under a pH 12 sodium hydroxide solution;
• resistance to strongly acid solutions defined as the time required to remove a 100 µm layer under a pH 0.3 nitric acid solution. For very low resistance glasses, the test is conducted using a pH 4.6 sodium acetate buffer solution;
• resistance to cleaning agents defined as the time required to remove a 100 µm layer using a pentasodium triphosphate solution;
• resistance to stain defined as the time required for a sodium acetate buffer solution to stain or color the lens;
• resistance to extreme climatic conditions defined as the time required to stain the lens under high humidity environments with temperature cycling between 40°C and 50°C.

All resistances are expressed as LOW, MODERATE or HIGH. When selecting ALL, no filtering is applied.

Glasses can be restricted by miscellaneous properties such as

• selecting only glasses that are resistant to radiation;
• selecting only glasses that are suitable for precision molding:
• selecting only glasses that have high UV transmission;
• selecting only glasses that do not contain lead;
• selecting only recent glasses;
• selecting only glasses that do not contain alkali;
• selecting only glasses that are available in high-precision batches where there is a tighter control on the refractive index and dispersion variation between the glass batch and the catalog value.

Glasses can be restricted by their supplier status including

• preferred glasses in the catalog;
• special and melt glasses;
• glasses with unknown status.