TECHNICAL NOTE
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Selecting a glass material is important since different glass types have different characteristics. Edmund Optics®
offers a wide variety of glass types which can be selected on the basis of the following characteristics. The
refractive index and dispersion (described using the Abbe number of a glass), are typically used by designers
as degrees of freedom when designing systems. Also, certain glass types have different transmission wavelength
regions. In addition, when designing an optic that will be used in an extreme environment it is important to realize
that each optical glass will have slightly different chemical, thermal, and mechanical properties. These properties
can be found on the glass datasheet.
REFRACTIVE INDEX
Refractive Index, n, describes how light slows down as it passes through an optical material. Defined as the ratio
of the speed of light in a vacuum to the speed of light in the specified material, the refractive index allows us to
predict how incident light will be affected by an optical element. Materials with higher index of refraction are easier
to fabricate into high numerical aperture components, whereas materials with lower index of refraction have inherently
less reflection when used uncoated.
n ≡
Speed of Light in Vacuum
c
=
Speed of Light in Material ν
c = 2,998 x 108 m/s
DISPERSION
Dispersion is a description of the variation of the refractive index with wavelength. Described using the Abbe
number, dispersion allows us to predict how much color separation to expect from an optical element. A low Abbe
number indicates high dispersion (more color separation) while a high Abbe number would indicate low dispersion
(less color separation).
vd ≡
(nd - 1)
(nF - nC)
nd = index of refraction at the Helium d-line, 587,6 nm
nF = index of refraction at the Hydrogen F-line, 486,1 nm
nC = index of refraction at the Hydrogen C-line, 656,3 nm
Glass Materials
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1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
300 400 500 600 700
Wavelength (nm)
Transmittance (5mm)
BOROFLOAT®
N-BK7
N-K5
B270
N-BaF10
N-SF5
N-SF10
N-SF11
N-LaSFN9
Glass GMlassa Mtateerriailsals
1
0.99
0.98
0.97
0.96
0.95
0.94
0.93
0.92
0.91
0.9
Glass GMlassa Mtateeriralisals
1400 1500 1600 1700 1800 1900 2000 2100 2200
Wavelength (nm)
Transmittance (5mm)
BOROFLOAT®
N-BK7
N-K5
B270
N-BaF10
N-SF5
N-SF10
N-SF11
N-LaSFN9
Glass
Name
Glass
Number
Schott
Equivalent
Ohara
Equivalent
CDGM
Equivalent
Density
(g/cm3)
Coefficient of
Linear Expansion*
Max Operating
Temp (°C )
Fused Silica 458/677 – – – 2,2 0,6 1000
BOROFLOAT® 472/657 BOROFLOAT® – – 2,2 3,3 450
S-FSL5 487/702 – – – 2,5 9,0 457
N-BK7 517/642 N-BK7 S-BSL7 H-K9L 2,5 7,1 557
N-K5 522/595 N-K5 S-NSL5 H-K50 2,6 8,2 546
B270 523/585 B270 – – 2,6 8,2 533
N-PK51 529/770 N-PK51 – – 3,9 12,4 487
ZERODUR® 542/562 ZERODUR® – – 2,5 0,1 600
N-SK11 564/608 N-SK11 S-BAL41 H-BaK6 3,1 6,5 604
N-BAK4 569/561 N-BAK4 S-BAL14 H-BaK7 3,1 7,0 555
N-BAK1 573/576 N-BAK1 S-BAL11 H-BaK8 3,2 7,6 592
L-BAL35 589/612 – L-BAL35 – 2,8 6,6 489
N-SK14 603/606 N-SK14 – – 3,4 7,3 649
N-SSK8 618/498 N-SSK8 S-BSM 28 – 3,3 7,1 598
N-PSK53A 618/634 N-PSK53A S-PHM52 – 3,6 9,6 606
N-F2 620/364 N-F2 S-TIM 2 H-F4 3,6 8,2 432
F2 620/364 F2 – – 3,6 8,2 434
S-BSM18 639/554 – S-BSM18 H-ZK11 3,7 7,0 613
N-SF2 648/338 N-SF2 S-TIM 22 H-ZF1 3,9 8,4 441
N-LAK22 651/559 N-LAK22 S-LAL54 H-LaK10 3,7 6,6 689
S-BAH11 667/483 – S-BAH 11 H-ZBaF16 3,8 6,8 575
N-BAF10 670/472 N-BAF10 S-BAH 10 H-ZBaF52 3,8 6,8 580
N-SF5 673/322 N-SF5 S-TIM 25 H-ZF2 4,1 8,2 425
N-SF8 689/312 N-SF8 S-TIM 28 H-ZF10 4,2 8,2 422
N-LAK14 697/554 N-LAK14 S-LAL14 H-LAK51 3,6 5,5 661
N-SF15 699/301 N-SF15 S-TIM35 H-ZF11 2,9 8,0 580
N-BASF64 704/394 N-BASF64 – – 3,2 9,3 582
N-LAK8 713/538 N-LAK8 S-LAL8 H-LAK7 3,8 5,6 643
S-TIH18 722/293 – S-TIH18 – 3,1 8,3 616
N-SF10 728/284 N-SF10 S-TIH10 H-ZF4 4,3 7,5 454
S-TIH13 741/278 – S-TIH13 – 3,1 8,3 573
N-SF4 755/276 N-SF4 S-TIH4 H-ZF6 3,2 9,5 570
N-SF14 762/265 N-SF14 S-TIH14 – 4,5 6,6 478
N-SF11 785/258 N-SF11 S-TIH11 H-ZF13 5,4 6,2 503
N-LASF45 800/350 N-LASF45 S-LAM66 H-ZLaF66 3,6 7,4 647
N-LASF44 803/464 N-LASF44 S-LAH65 H-ZLaF50B 4,5 6,2 666
N-SF6 805/254 N-SF6 S-TIH 6 H-ZF7LA 3,4 9,0 605
N-SF57 847/238 N-SF57 S-TIH53 H-ZF52 5,5 8,3 414
N-LASF9 850/322 N-LASF9 S-LAH71 – 4,4 7,4 698
S-NPH2 923/189 – S-NPH2 – 3,6 6,7 604
N-SF66 923/209 N-SF66 – – 4,0 5,9 710
S-LAH79 003/283 – S-LAH79 – 5,2 6,0 699
GLASS NUMBER
For ease of comparing materials, including comparing equivalent
materials from alternate glass manufacturers, a common international
glass code exists. The code can be used to locate any glass
on the Abbe Diagram. The first 3 digits in the glass number reflect
the refractive index nd (removing any numbers prior to the decimal
point), and the second 3 digits reflect the Abbe Number νd (removing
the decimal point from the number). For example, N-BK7 has
an index of refraction of 1,517 and an Abbe number of 64,2; its
corresponding glass number is 517/642.
Many glass manufacturers offer the same material characteristics
under different trade names and have modified their products and
processes to be ECO-friendly (free of lead and arsenic). Edmund
Optics® only uses ECO-friendly, RoHS compliant materials unless
otherwise noted. Based on availability, we reserve the right to substitute
equivalent materials from a variety of approved glass suppliers.