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n this section we present the vacuum windows (viewports) from Allectra.
For applications where the user only wants to see what is happening in the vacuum chamber, Kodial (boro-silicate) glass is the best choice as it has a low cost and is available on a wide range of flange types and sizes.
Fused silica is synthetically made quartz. It is a very pure material with minimal inclusions or bubbles. Viewports made from this material extend the transmission to the Ultra Violet (UV) and near Infra Red (IR) range.
The full range of materials is shown on the right.
The quality of polishing is normally given by two numbers called scratch/dig. The first one refers to the maximum width of a scratch in μm, the second gives the diameter of digs or bubble defects in 10 μm. So, a typical polish of 40/20 refers to a maximum scratch width of 0.04 mm and a maximum dig diameter of 0.2 mm. Two digs must be separated by minimum 20 mm from each other

The range of materials is shown below:

Kodial glass.

Sapphire: Standard, UV Grade & DUV Grade.

Fused silica: UV Grade, DUV, EXCIMER Grade, near IR Grade and non- magnetic.

Crystal quartz.

Calcium fluoride / Magnesium fluoride.

Zinc selenide.

Beryllium.

Information about each type available

STANDARD VIEWPORTS

alt="Standard viewports"

We can offer standard glass viewports, on CF, KF and ISO-K flanges. The standard glass material used is Kodial (boro-silicate glass). These viewports are for normal visible light; for more demanding applications, we recommend the use of fused silica (quartz).

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SAPPHIRE VIEWPORTS

alt="MIRILLA ZAFIRO"

Sapphire has high transmission over wavelengths from 180 nm up to 5500 nm. It is a very rigid material with high bakeout temperatures making sapphire an ideal material for many demanding applications. Allectra offer three qualities: regular grade, UV and Deep UV sizes up to 136 mm view. Broad band or single band coated versions are available on request.

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FUSED SILICA VIEWPORTS

alt="FUSED SILICA VIEWPORTS"

Fused silica is an isotropic material with no crystal orientation. It has an almost flat transmission curve from UV to near IR with more than 90% transmission in the visible range. Three qualities are offered: UV grade (200nm to 2 μm) / DUV grade (200nm to 2 μm – high purity) and EXCIMER grade (185nm to 2.2 μm). UV-grade quartz is offered for use with KF flanges. Other fused silica grades are available on request.

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LASER VIEWPORTS

alt="LASER VIEWPORTS"

For laser applications, Allectra offers high quality quartz viewports with optimised coatings. All viewports have more than 99.5% transmission/surface at the given wavelength. A high quality 20/10 surface finish and a flatness of λ/4 allow high performance. They are offered on 40 CF flanges with 35 mm view diameter and on 63 CF with 68 mm view diameter.

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SPECIAL MATERIAL VIEWPORTS

alt="SPECIAL MATERIAL VIEWPORTS"

UHV viewports made of special materials are available when other wavelengths than standard glass or quartz are needed. Calcium-fluoride and magnesium-fluoride cover a wide transmission range from UV to infrared down to 20 μm. With the optional AR coating, higher transmission can be reached.

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SPECIAL PURPOSE VIEWPORTS

alt="SPECIAL PURPOSE VIEWPORTS"

Re-entrant windows allow optional systems or cameras to be inserted “inside” the vacuum system. Other tube lengths can be offered on request. Differentially-pumped viewports for XHV: These special windows are used typically for Geo-chronology measurements. Two UHV windows are sealed together and can be differentially pumped. Coated Cleartran gives good transmission from 350 nm to the far IR. Beryllium X-rya viewports act as a barrier between the vacuum or inert gas environment inside an X-ray source tube or detector and atmospheric conditions external to the device, while at the same time allowing X-rays to pass through. Standard size is 40 CF with a thickness of 130 μm and a view diameter of 39 mm.

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