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Technical Reference : Characteristic of Glass Materials

The glass materials used by Sigma Koki can be roughly classified into one of two groups, depending on their intended use: glass for total reflection and glass for transmission. Since optical materials for total reflection applications use only their surfaces and do not demand special materials, they are selected for convenience in polishing and thermal stability of the polished surfaces. In contrast, optical materials for light transmission applications use both the surfaces and the interior, making characteristics such as transmittance, homogeneity, and presence or absence of internal bubbles important, in addition to properties of total reflectance glass material. The refractive index of glass is a major consideration for lenses that refract light, while both light dispersion and refractive index are important for prisms and combination lenses. Glass for light transmission applications is carefully selected from several hundreds types of optical glass, after considering optical characteristics, as wel l as characteristics such as cost and chemical and physical properties.

Typically of higher quality than ordinary glass, optical glass has specific refractive indices and must meet certain requirements for striae, bubbles, and other characteristics.

BK7 Symbol "B"

Features

BK7 is a borosilicate optical glass.

Used as substrates for small sized mirrors and transmissive optics.

Chemically stable and surfaces not easily tarnished.

Relatively hard compared to other optical glasses and prevent scratches.

Highly homogeneous with a low bubble and inclusion count.

High transmittance through the wavelength range of 350 to 2000nm.

Inexpensive and readily available due to the mass production.

Synthetic Fused Silica Symbol "SFS"

Features

An optical material, which commonly used in UV region.

Has extremely low thermal expansion (1/10 of BK7), making it an ideal substrate material for high precision mirrors.

Due to the manufacturing process, fused silica contains hydroxyls and therefore contains absorption bands at 1.38μm, 2.22μm, 2.72μm.

High UV and visible transmission.

Highly homogeneous with a low bubble and inclusion count.

Usable through broad temperature ranges in excess of 800°C.

Low fluorescence in UV.

Very hard and difficult to scratch making it easy to clean.

Water Free Fused Silica Symbol "NQ"

Features

Plasma manufacturing method produces less absorption through the IR region preventing the generation of hydroxyls.

Relatively expensive material due to the large electric consumption during manufacturing.

Suitable to use as a substrate for transmissive optics.

Pyrex® Symbol "PX"

Features

Similar to BK7, Pyrex® is classified as a borosilicate glass and common for scientific use.

Has relatively low thermal expansion (1/2 of BK7) and therefore used as a medium sized mirror substrate.

Since Pyrex® is not an optical glass, it often contains bubbles, impurities and striae (inhomogeneity).

Easy to polish and difficult to scratch making it easy to handle and clean.

B270-SUPERWHITE (White Glass)

Inexpensive and high transparent crown glass with a transmittance is similar to BK7.

Readily available making it easy to procure.

White glass is suitable for low precision optics only.

Other Optical Glasses / Specialty Glasses

High refractive index glass LaSFN9, and medium refractive index glass SK2 are both used as the material of lenses because of its excellent chemical and mechanical characteristics for fabrication.

Excimer Laser Grade Synthetic Fused Silica Symbol "SFSK"

Excimer laser grade fused silica is produced by controlling the amount of hydroxyls contained inside fused silica, and therefore shows high durability when irradiated by excimer laser light.

Sigma Koki manufactures standard catalog lenses using excimer laser grade fused silica. Parts are normally made by fused silica, which is suitable for use with 248nm excimer lasers. Please ask to our sales when using with 193nm excimer lasers.

When optical glass is irradiated by strong UV light, transmittance falloff or color center formation will occur and therefore periodical replacement of the optics is required.

Irradiating Laser Intensity Repetition Irradiating Time Inspection Standard
Ar*F(193nm) Grade Synthetic Fused Silica Ar*F Excimer Laser 10mJ/cm2 100Hz 17min No Fluorescence
Kr*F(248nm)Grade Synthetic Fused Silica Kr*F Excimer Laser 50mJ/cm2 25Hz 2min No Fluorescence

Characteristics of Optical Glass

Wavelength (nm) BK7 SK2 LaSFN9
Refractive Index 334.1 1.54272 1.64304 -
365.1 1.53627 1.63398 -
404.7 1.53024 1.62562 1.89844
480 1.52283 1.61547 1.87059
546.1 1.51872 1.60994 1.85651
587.6 1.5168 1.60738 1.85025
632.8 1.51509 1.60513 1.84489
706.5 1.51289 1.6023 1.83834
852.1 1.5098 1.59847 1.82997
1060 1.50669 1.5949 1.82293
1529.6 1.50091 1.58914 1.81363
1970.1 1.49495 1.58378 1.80657
2325.4 1.48921 1.57881 1.80055
Density (g/cm3) 2.51 3.55 4.44
Thermal Expansion Coefficient (x10-6) 7.1(-30 to 70°C) 6.0(-30 to 70°C) 7.4(-30 to 70°C)
Thermal Conductivity (W/m / K) 1.114 0.776 -

Extracted from SHOTT catalog.

Characteristics of Glass Materials

Wavelength (nm) Synthetic Fused Silica Pyrex® B270-SUPERWHITE
Refractive Index 193 1.561 - -
200 1.548 - -
300 1.486 - -
350 1.476 1.48 -
400 1.47 1.478 -
500 1.462 1.474 1.5251(546nm)
600 1.458 1.472 1.5230(588nm)
700 1.455 - -
800 1.453 - -
1000 1.451 - -
1500 1.445 - -
2000 1.438 - -
2500 1.43 - -
3000 1.419 - -
3500 1.407 - -
Transmissive Range (μm) 0.19 to 3.5 0.38 to 2.3 0.35 to 2.5
Reflection Loss (per surface at 500nm) 3.50% 3.7% 4.30%
Density (g/cm3) 2.2 2.23 2.55
Thermal Expansion Coefficient (x10-6) 0.55 3.25(20 to 300°C) 9.4(20 to 300°C)

Optical Characteristic of BK7 and Synthetic Fused Silica (Reference Data)

Transmittance

Refractive index

Refractive Index (n) & Transmittance (T)

Wavelength (nm) Synthetic Fused Silica BK7 Light Sources Mark Spectral Region
n T(%) n T(%)
165 VUV
166 0 VUV
167 20 VUV
168 35 VUV
169 46 VUV
170 50 VUV
173 75 VUV
175 80 VUV
180 84 VUV
185.4 85 VUV
190 86 VUV
193.5 1.561 87 VUV
200 1.548 88 UV
210 1.54 90 UV
220 1.534 91 UV
230 1.523 91 UV
240 1.515 92 UV
250 1.509 92 UV
260 1.502 92 UV
270 1.497 92 UV
280 1.493 92 UV
290 1.489 92 0 UV
300 1.486 92 15 UV
313.2 1.484 92 1.548 38 UV
325 1.483 92 1.545 58 He-Cd laser UV
334.2 1.48 93 1.543 72 UV
337.1 1.48 93 1.541 76 N2laser UV
351.1 1.476 93 1.539 85 Ar laser UV
355 1.476 93 1.539 88 YAG(3) UV
363.8 1.475 93 1.536 90 Ar laser UV
365 1.475 93 1.536 90 Hg i UV
398.8 1.47 93 1.531 90 violet
404.7 1.47 93 1.53 92 Hg h violet
435.8 1.467 93 1.527 92 Hg g blue
441.6 1.466 93 1.526 92 He-Cd laser blue
457.9 1.465 93 1.525 92 Ar laser blue
465.8 1.464 93 1.524 92 Ar laser blue
472.7 1.464 93 1.523 92 Ar laser blue
476.5 1.464 93 1.523 92 Ar laser blue
480 1.464 93 1.523 92 Cd F' blue
486.1 1.463 93 1.522 92 H F blue
488 1.463 93 1.522 92 Ar laser blue
496.5 1.462 93 1.522 92 Ar laser green
501.7 1.462 93 1.521 92 Ar laser green
514.5 1.461 93 1.52 92 Ar laser green
532 1.461 93 1.519 92 YAG(2) green
546.1 1.46 93 1.519 92 Hg e green
587.6 1.458 93 1.517 92 He d yellow
589.3 1.458 93 1.517 92 Na D orange
632.8 1.457 94 1.515 92 He-Ne laser red
643.9 1.457 94 1.515 92 Cd C' red
656.3 1.456 94 1.514 92 H C red
694.3 1.456 94 1.513 92 RUBY laser red
706.5 1.455 94 1.513 92 He r red
830 1.452 94 1.51 92 GaAIAs NIR
852.1 1.452 94 1.51 92 Cs s NIR
904 1.452 94 1.509 92 GaAs laser NIR
1014 1.45 94 1.508 92 Hg t NIR
1064 1.449 94 1.507 92 YAG laser NIR
1100 1.449 94 1.507 92 NIR
1200 1.448 93 1.505 92 NIR
1300 1.447 93 1.504 92 NIR
1350 1.447 91 1.504 92 NIR
1380 1.446 83 1.503 88 NIR
1400 1.446 87 1.503 91 NIR
1500 1.445 93 1.501 91 NIR
1600 1.443 94 1.5 91 NIR
1700 1.442 94 1.499 91 NIR
1800 1.441 94 1.497 88 NIR
1900 1.44.0 94 1.497 85 NIR
2000 1.438 94 1.495 83 NIR
2100 1.437 92 1.493 81 NIR
2200 1.435 67 1.492 73 NIR
2220 1.434 56 1.492 71 NIR
2250 1.434 64 1.491 70 NIR
2300 1.433 80 1.49 72 NIR
2400 1.431 87 1.487 65 NIR
2500 1.43.0 73 1.485 59 MIR
2600 1.428 58 1.484 55 MIR
2650 1.427 20 1.483 40 MIR
2700 1.426 0 1.483 30 MIR
2720 1.426 0 1.482 23 MIR
2750 1.425 0 1.481 19 MIR
2800 1.424 0 9 MIR
2900 1.422 40 0 MIR
3000 1.419 65 MIR
3100 1.417 75 MIR
3200 1.414 78 MIR
3300 1.412 81 MIR
3400 1.409 80 MIR
3500 1.407 70 MIR
3600 61 MIR
3700 50 MIR
3800 25 MIR
3900 21 MIR
4000 23 MIR
4100 15 MIR
4200 4 MIR
4300 0 MIR

ZERODUR® (Reference data)

Features

A crystallized glass manufactured by SHOTT GLAS (Germany). Once melted at high temperature and then subjected to heat treatment in which the glass undergoes a crystalline growth stage.

Optical Property etc.

Transmissive Range 0.4 to 2.5μm
Refractive Index 486.1 nm 1.5491
587.6 nm 1.5424
656.3 nm 1.5394
Surface Reflection Loss 4.6% per surface (at 587.6 nm)
Specific Gravity 2.53
Average Thermal Expansion Coefficient 0±0.10×10-6/K (0 to 50°C)

ZERODUR®is registered trademark of SHOTT GLAS.

Thermal Expansion Ratio

Transmittance

CLEARCERAM®-Z (Reference data)

Features

CLEARCERAM®-Z is a crystallized glass developed by OHARA INC. and has an extremely low thermal expansion and high transparency.

A material which shows excellent characteristics in heat-resistance, hardness, mechanical strength, chemical durability and processability.

Optical Property etc.

Transmissive Range 0.4 to 2.5μm
Refractive Index 587.6nm 1.546
Surface Reflection Loss 4.6% per surface (at 587.6 nm)
Specific Gravity 2.55
Thermal Expansion Coefficient 0.0±1.0×10-7/°C
Degasification Analysis No detection of metallic element (30°C to 1000°C)

CLEARCERAM®is registered trademark of OHARA INC.

Thermal Expansion Ratio