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Optical blank

Category： Optical Glass Blank

Overview Introduction

The optical homogeneity is defined as the maximum variation of the refractive index An

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Product Introduction

1.10ptical Homogeneity

1.2.1 Large Aperture Optical Glass

The optical homogeneity is defined as the maximum variation of the refractive index An... within a piece of glass. △nmax is measured by the method specified in GB/T 7962.2-2010,and classified into 6 grades (Table 1):

Grade	△nmax
H₀₀	0.5x10^-6
H₀	1x10^-6
H₁	2x10^-6
H₂	5x10^-6
H₃	10x10^-6
H₄	20x10^-6

1.2 Stress Birefringence

1.2.1 Middle Stress

The middle stress existing in the glass blank is measured by the method specified in GB/T 7962.5-2010. Optical path difference δ in nm/cm is measured along the longest direction of glass blank, and the middle stress reflects optical path difference per unit in the middle section. It is classified into 4 grades (Table 2):

Grade	δ（nm/cm)The optical path difference at the center of glass δ
1	2
1a	4
2	6
3	10

1.2.2 Edge Stress

It is measured by the method specified in GB/T 7962.5-2010, measuring the optical path difference at a distance of 5% of the diameter or from the longer side of glass blank. Edge stress (nm/cm) is defined by maximum optical path difference δ max per unit thickness and classified into 4grades(Table3):

Grade	δmax（nm/cm)The optical path difference at the edge of glass δmax
S₁	2
S₂	5
S₃	10
S₄	20

1.2.3 Stress Birefringence Requirements for Coarse Annealed Glass

For coarse annealed glass with the thickness smaller than orequalto 20mm, edge stress birefringence shall be smaller than or equal to 100nm/cm. For coarse annealed glass with the thickness greater than 20mm,the edge stress birefringence shall be smaller than or equal to 80nm/cm.

1.4lnclusions

Weight of inclusions in optical glass is measured by the method in GB/T 7962.8-2010, the content of allowed inclusionsin glass is decided by the total cross sectional area of inclusions (diameter Φ >0.03mm) in 100cm' glass and the inclusions are divided into 5 Grades, see Table 4.Cross sectionarea of flat long inclusions is calculated by arithmetic meanvalue of the longest shaft and the shortest shaft as the diameter.

Grade	Total cross section area of inclusions with the diameter Φ ≥0.03mm in every 100cm³glass
A₀₀	S≤0.03
A₀	0.03<S≤0.10
A	0.10-S<0.25
B	0.25<S≤0.50
C	0.50<S≤1.0

1.5 striae

With the striae-scope,striae isviewed in the direction of maximum visibility.By comparing with a standard sample, the striae is classified into 4 grades.(Table 5):

Grade	Striae feature
A	Invisible to the naked eye
B	Fine and scattering striae
C	Slight parallel striae
D	Obvious parallel striae

1.6 Coefficient of Optical Absorption

It is measured with spherical photometer by the method specified in GB/T7962.9-2010. There is internal transmittance when the white light passes the path per cm,then the coefficient of optical absorption equals the negative value of the natural logarithm of such internal transmittance.According to thevalue,the quality is divided into 8 grades (Table 6):

Grade	The max.coefficient of optical absorption
00	0.001
0	0.002
1	0.004
2	0.006
3	0.008
4	0.010
5	0.015
6	0.030

2.1Blank

2.1.1 Direct-press Blank

Direct -press blank is directly formed from melted glass, and is fine annealed.

2.1.2 Reheated-Press Blank

Reheated-press blank is formed by reheated - press process,and is fine annealed (Table 7):

Outer diameter Φ （mm）	DP		RP
Outer diameter Φ （mm）	Outer diameter tolerance（mm）	Thickness tolerance（mm）	Outer diameter tolerance（mm）	Thickness tolerance（mm）
Φ<15	±0.10	±0.20	±0.10	±0.50
15≤Φ<29	±0.10	±0.20	±0.15	±0.35
29≤Φ<40	±0.15	±0.20	±0.20	±0.30
40≤Φ<60	±0.20	±0.20	±0.30	±0.30
60<Φ<90	±0.30	±0.40	±0.35	±0.35
90≤Φ<150	±0.40	±0.40	±0.40	±0.40
Φ≥150	±0.50	±0.50	±0.50	±0.50