SCHOTT Technical Glasses

26
Optical glass
The term “optical glass” is used in distinction to “technical
glass” for a specific group of glasses mainly for optical
applications like imaging in the UV, visible, and infrared
wavelength range. These applications require a broad set
of glasses with high transmission and well defined refractive
index and specific dispersion properties (described by
Abbe-numbers). Combinations of these glasses allow for
the construction of high-performance optical systems.
Up to 17 or more different raw materials with the lowest
level of impurities to avoid absorption by coloring elements
are used to achieve the desired specifications. Each optical
glass is described (beside others) by its coordinates in the
so-called “Abbe-Diagram” (see Figure 23).
Optical filter glass
Optical filter glass is known for its selective absorption in
certain wavelength ranges. The absorption within the glasses
is caused either by ions of heavy metals or of rare earths or
it is caused by nano crystals within the glass matrix. By combining
different coloring agents a wide range of different
filter functions (neutral density filters, longpass filters, short
pass filters and bandpass filters) can be obtained. Figure 25
depicts special UV bandpass filters that have a region of
high internal transmittance in the UV and high absorption
for visible light.
As an alternative to bulk filter glasses, coated interference
filters are used. Here a transparent glass substrate is coated
with a set of thin transparent layers of e.g. oxidic materials
with different refractive indices. The spectral properties of
these filters are defined by interference effects.
Optical filter glass and inteference filters are optimized for
industrial applications, thus the main focus is the reproducibility
of spectral transmittance. However, these glasses
appear to be colored if their filter effect lies within the visible
light spectrum.
Chalcogenide glass
In most known glass types, oxides of e.g. silicon, phosphorous,
lanthanum and borate are building the glass forming
network. Though some oxidic glass types with special compositions
melted under very dry conditions show transmittance
until 4 – 5 microns, the absorption of the cation-O-bond
in the network sets a limit to the (mid – far) infrared (IR)
transmission of these glasses. The main characteristic of
chalcogenide glasses is the complete replacement of the
element oxygen by other elements of the chalcogenide
group like sulfur, selenium or tellurium to extend transmittance
further into the mid to far IR. For instance, SCHOTT IR
chalcogenide glasses (IRG) exhibit high transmission from
the visible range to beyond 12 µm into the far infrared (see.
Figure 24).
2.05
95
ν d
90
85 80 75 70 65 60 55 50 45 40 35 30 25 20
35
2.05
Transmission of IRG 22–26
80
Thickness 10.0 mm (Typical Values)
2.00
1.95
1.90
Abbe-Diagram n d –ν d
Description of Symbols
Lead and arsenic free N- or P-glass
Classical crown and flint glass
Glass available as N-glass or classical flint glass
46A
46B
68
66
67
2.00 n d
1.95
1.90
70
60
n d
85 80 75 70 65 60 55 50 45 40 35 30 25 20
1.85
Glass suitable for precision molding
HT – High transmittance glass
HTultra – Ultra high transmittance glass
31A
LASF
9
57
1.85
50
1.80
* Available in step 0.5
21
44*
33
41
51 50
47 43
40
45
56A
6
*
SF
11
1.80
40
1.75
1.70
1.65
1.60
1.55
1.50
1.45
95
58
90
51A*
52 A
FK
51*
PK
PSK
5*
10
53A*
3
7*
BK
LAK
16
60
4
14
5 57SK
11
21
58A
7
ZK7
5
2
7
57Q1
1
4
BAK
K
22
10
34
14
9*
12
2*
8
4
5
33A
2
35
5
SSK
BALF
KZFS2*
KF
9
33B
10
8
34
35
10
LLF
37
2
51
BAF
KZFS4*
52
1
4
LF
LAF
64
BASF
2
KZFS5* 2*
KZFS11*
5
5
F
2
7
KZFS 8*
5*
8
15
10
69
1
4
14
1.75
1.70
1.65
1.60
1.55
1.50
1.45
March 2015
Transmission in % ––>
30
20
10
0
0 2000 4000 6000 8000 10000 12000 14000 16000 18000
Wavelength in nm ––>
IRG 22 IRG 23 IRG 24 IRG 25 IRG 26
ν d
Fig. 23. SCHOTT Advanced Optics Abbe-Diagram that gives an overview
of SCHOTT’s optical glass types
Fig. 24. Transmission of IRG 22 – 26