K9 (BK7) has excellent mechanical properties and very low bubble k9 (b270) product map and impurities, and has good scratch resistance. Due to its stable chemical properties, no special treatment for grinding and polishing is required. It is used in many fields such as optoelectronics, microwave technology, and diffractive optical elements.

Attributes	Explanation
Transmission range	0.4µm to 2.5µm
Density	2.51 g/cc
Thermal expansion	7.1x10-6 /°k @ -30° + 70°c, & 8.3x10-6 /°k @ 20°c to 300°
Surface polishing	bk-7 polishes extremely well & polishes of 10-5, or 20-10 scratch-dig are achieved at extra costs respectively, mainly for uv & visible applications.
Surface graph	surface figure of 1/10 wave to 1/4 wave @ 0.6328µm are specified mostly on lenses for ultraviolet & visible use.
Coating	ar @ 0.8-2.5µm, ar @ 1.064, ar @ visible wavelength.
Application	Astronomy, thermal imaging
Products produced	Lenses, prisms, filters, filters, etc.

Wavelength	Refractive index (n)
0.4047	1.530
0.4800	1.523
0.5461	1.519
0.6328	1.515
0.8521	1.510
1.0600	1.507
1.5300	1.501
1.9700	1.495
2.3250	1.489

China-K9: Nd: 1.516371 Vd: 64.13356

Short-BK7: Nd: 1.516800 Vd: 64.169998

HOYA-BSC7: Nd: 1.516800 Vd: 64.2

Borosilicate glass

B270

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