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Ultra-High Vacuum (UHV) Viewports

What are the Ultra-high vacuum (UHV) viewport applications?

UHV viewports allow a user either visual or instrumental access (e.g. a laser) to the vacuum chamber. This access may be as simple as a viewing window used to see into the chamber or a more complex custom-coated version which allow the passage of certain wavelengths (typically lasers or non-contact thermal imaging) both in & out of the vacuum system. The window material of the viewport is chosen to be sufficiently transparent over the wavelength range of interest, so an optically transparent glass window would allow the user to see into the system, whereas silicon is optically opaque but transmits wavelengths into the far IR for THz applications. The choice of material, sealing mechanism and coating must also be able to withstand the physical and chemical conditions which it will encounter, including any vacuum bake requirements.

Available Viewport Types


For more information, please see our catalogue

Magnetic/Non-magnetic Viewports

(New pages coming soon)

Brazed Fused Silica Zero Length Viewports

Coated Viewports

(New pages coming soon)

Lead-Glass Viewports

(New pages coming soon)

Aerospace Vacuum Windows

(New page coming soon)

Re-entrant Viewports

(New pages coming soon)

Brewster Windows

(New page coming soon)

Differentially-Pumped Viewport

(New page coming soon)

Water-Cooled X-Ray UHV Viewport

(New page coming soon)

Viewport Shutters

(New page coming soon)

Viewport Accessories

Our Ultra-High Vacuum (UHV) Viewport Window Material Selection

There are a wide range of optical materials available as standard, the choice will depend on many things including mounting flange, seal type, optic size, cost, temperature extremes and the wavelength ranges of interest. Common examples are listed below, this is not an exhaustive list, we are prepared to consider other materials that customers may specify.

  • Borosilicate (Kodial) glass viewports are optically transparent in the visible range and used to see what is going on inside the vacuum system. Typical applications may involve observing sample transfer, checking if valves are open or closed, or monitoring processes or active components. Borosilicate viewports are manufactured by hermetically sealing the edge of the glass optic onto a metal spinning to form a vacuum leak-tight seal. This is then welded into an appropriate vacuum flange. Borosilicate glass is also known as 8250 or 7056 glass.
  • Fused silica has high transmission in the ultraviolet (UV) range of the spectrum. The good optical properties make it ideal for use in laser applications where precision optics are required. The optics are vacuum brazed into a variety of metal spinnings. Different metal spinning materials allow the production of low or non‑magnetic viewports. We can also offer high performance fused silica grades such as Spectrosil®, Infrasil®, & HPFS 7980® in addition to our standard UV grade.
  • Sapphire has a broad transmission range from UV to near infrared, it also works well at high temperatures. Sapphire is vacuum brazed and is available in standard, low or non-magnetic versions.
  • Natural z-cut quartz has natural birefringent properties, The material is cleaved along the Z axis (z-cut) such that the optic axis of the crystal is perpendicular to the flat surfaces causing the ordinary and extraordinary rays to follow the same path through the crystal and maintain the polarization of the beam. Transmission takes place in the ranges 250nm to 3µm, and from 50µm to 1000µm+ making it an ideal THz material. We offer z-cut viewports in a bonded mounting as the material cannot withstand the high temperatures (above 490°C) associated with vacuum brazing.
  • Zinc selenide (ZnSe) is recognisable by its distinctive yellow colour. It offers high transmission in the infrared range. It is one of the materials of choice for CO2 laser optics operating at 10.6 microns. Applications include thermal imaging.
  • Magnesium fluoride (MgF2) transmits in both UV and near infrared ranges, it is commonly used for excimer laser applications. As standard we supply this material in the C-cut orientation for minimum birefringence.
  • Calcium fluoride (CaF2) transmits in both UV and near infrared ranges, used for excimer laser applications.
  • Barium fluoride (BaF2) transmits in both UV and near infrared ranges, it performs slightly better in the IR region than CaF2 (and worse in the UV region), typical applications include thermal imaging (non-contact temperature measurement) and thermal spectroscopy.
  • Lithium fluoride (LiF) transmits from around 150nm to 6µm, it is valued for the 150nm to 200nm range (VUV). It has a low refractive index. A popular use is for thermal imaging (non-contact temperature measurement).
  • CVD diamond is the ultimate optical material transmitting from UV to the far infrared making it an excellent material for THz applications. We offer both optical and X-ray versions of the material which differ by their transmission in the UV and visible ranges.
  • Potassium bromide (KBr) A good material for far IR transmission, it is however susceptible to attack by moisture, so precautions need to be made to preserve it. We can offer the material with a conformal coating for protection.
  • Zinc sulphide (ZnS) A good material for-IR, especially in the 8 to 14µm range. It is also a tough material allowing it to withstand harsh environments. It must not be heated above 250°C.
  • KRS5 (thallium bromo-iodide) KRS5 has deep IR properties and has a high refractive index. It is widely used in spectroscopy applications. It is non-hygroscopic so is used for liquid cell windows in FTIR spectroscopy, making it a suitable alternative to the other hygroscopic optical materials. As a disadvantage, the material is considered toxic so needs careful handling and storage. The material can also cold flow over time, so the material needs to be regularly inspected.
  • Germanium (Ge) Germanium transmits fairly well between 2 µm and 14 µm and so is suitable for applications in thermal imaging and measurement. Its high refractive index (4 at 11 µm) gives it a high intrinsic reflectivity so that it can be used as a beamsplitter without special coatings. Components such as ATR (attenuated total reflection) heads for IR spectrometers are often made from germanium. It can also be used for electromagnetic shielding.

Torr Scientific’s Coated Viewports Selection


  • Indium tin oxide (ITO) – A thin conductive coating normally applied to the vacuum side of the optic to reduce the build-up of static charge. It can also be applied to the atmosphere side of the optic as a microwave blocker.
  • Anti-reflective (AR) coating – a single 1 x QWOT MgF2 layer on both sides of the window optimised to a customer-specified wavelength range.
  • Broadband (BBAR) anti-reflective coating – a four-layer coating on both sides of the optic optimised to a customer-specified laser wavelength range.
  • VAR anti-reflective coating – a two-layer coating on both sides of the optic optimised to a customer-specified laser wavelength.
  • WAR anti-reflective coating – a four-layer coating on both sides of the optic optimised to a customer-specified laser wavelength.
  • SPAR anti-reflective coating – a multilayer layer on both sides of the optic optimised to a customer-specified laser wavelength, this may involve multiple target wavelengths or very wide wavelength coverage.
AR, BBAR, VAR and WAR anti-reflective coating curves comparison

Typical curves for the various coatings

A range of anti-reflective coatingstailored to the specific requirements of the customer’s application, can be added to our viewports.
Visit our Anti-Reflective Coatings page for further details and example reflectance curves.

Mounting Flange Selection

Torr Scientific viewports are offered on a wide range of vacuum mounting flanges. UHV Conflat® CF versions are offered using 304L or 316LN stainless steel flanges. Non-magnetic viewports are offered using high-grade 316LN or titanium. Flanges in 304L stainless steel are used for the high vacuum KF and ISO viewports, 316L is also available as an optional material.

We also offer custom flanges manufactured to customer requirements. It is also possible to mount multiple windows onto a single flange if required. Please contact our sales office with your requirements.


CF Flange

KF Flange

ISO Flange

Laser damage threshold

Our standard laser damage threshold (LDT) for pulsed lasers is 2 J/cm2 for wavelength 530 nm and pulse width 10 ns. This threshold varies with wavelength and pulse width. For ultrafast lasers with picosecond or femtosecond duration or even shorter, a non-thermal damage mechanism from the interaction of the laser electric field with the bonds of the material can become important, so the scaling of the damage threshold to these regimes is not meaningful. This standard LDT is based on a very conservative estimate of what we expect our coatings to be able to withstand.

Our standard laser damage threshold (LDT) for continuous wave (CW) lasers is 500 W/cm2 at wavelength 530 nm, again a conservative estimate of the limits of our coatings. This threshold scales in proportion to wavelength. Our coatings have successfully passed laser damage tests using a beam with power density of 138 kW/cm2, but allowing for the fact that the beam was incident at 45°, spreading the power over a larger and marginally increasing reflectance losses, this is equivalent to over 96 kW/cm2, suggesting that our standard LDT has factor of safety, in this instance, of nearly 200.

More recent research indicates that a more sophisticated approach to CW threshold is needed as the threshold expressed as areal power density (as above) also scales with beam diameter. When a sufficient body of test data has been accrued, we will consider redefining our CW threshold in linear units of W/cm, such that it will naturally account for beam diameter.


Features and Benefits of UHV Vacuum Viewports

  • Wide range of optical materials = allows users to choose the best material for their application
  • CF, KF, & ISO flanges as standard options = suitable for all vacuum systems
  • Online catalogues and price lists = Allows customers to view product range and specifications
  • Custom fabrications can be made = When no standard part will fit
  • Design service available = Rough sketches can be turned into final manufactured products
  • 26 years manufacturing experience = We’ve probably seen your special before
  • Custom AR coatings = When ‘out of the box’ won’t do, we can offer that coating
  • Environmentally packaged = Helps save the planet


Why Choose Torr Scientific for UHV Vacuum Viewports?

  • High product quality
  • Wide range of optical materials and compatible mounting flanges
  • Custom AR coatings available for many materials
  • Viewports and coatings are manufactured together in the same UK factory
  • Competitive pricing in GBP (£), Euro (€) and USD ($)
  • Fast deliveries
  • 26 years manufacturing experience
  • Team of dedicated engineers and scientists for technical support
  • Custom viewports can be manufactured to customer requirements
  • Fully traceable lead-free materials and processes


What can Torr Scientific do for you?

Torr Scientific manufactures a range of competitively priced ultra-high vacuum (UHV) viewports with Kodial (borosilicate glass), fused silica, sapphire, natural z-cut quartz, zinc selenide (ZnSe), magnesium fluoride (MgF2), calcium fluoride (CaF2), barium fluoride (BaF2), CVD diamond, lead glass, lithium fluoride (LiF), potassium bromide (KBr), zinc sulphide (ZnS). KRS5 (thallium bromo-iodide) and more. Designs are rated for high and ultra-high vacuum (UHV) applications.

Full transmission, dimensional, optical and temperature specifications can be viewed on the viewport section of the catalogue.

Custom-designed viewports can be quoted on request.

All of our viewports are lead (Pb) free! So fully RoHS compliant.

A range of anti-reflective coatings, tailored to the specific requirements of the customer’s application, can be added to our viewports. Visit our Anti-Reflective Coatings page for further details and example reflectance curves.

Where and how Torr Scientific’s (UHV) viewport applications are manufactured?

Viewports at TSL are manufactured at our clean facility in Bexhill, near Hastings in East Sussex, UK. The widow is hermetically sealed into a metal ring which is then welded into the vacuum flange. Most of the specialised coatings, such as anti-reflective coatings or transparent conducting films are applied in‑house. All viewports are helium leak‑checked and cleaned to UHV standards before release to the customer. They are supplied ready for immediate use without additional processing required.

Product Enquiries

Torr Standard Enquiries Form

Click here for the latest GBP (£) Price List for the Vacuum Optics

Click here for the latest USD ($) Price List for the Vacuum Optics

Click here for the latest EUR (€) Price List for the Vacuum Optics

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