Vacuum Optics ❯ Viewports ❯ Brewster windows

Brewster windows

What are Brewster windows?

Torr Scientific offers fully customisable Brewster windows, which can be used for polarising optical beams and as an alternative to anti-reflective (AR) coated optics.

These are custom designed, taking the requested optical material and desired wavelength to calculate the level of reflectance and the Brewster angle.

Using these values, we can manufacture an optic that partially reflects s‑polarised light and fully transmits p-polarised light, without requiring any antireflective coatings.

We offer many customisations for our Brewster windows including numerous options for the optical material, flange style and flange size. 

All our Brewster windows are helium leak tested, cleaned and packed to UHV standards on site at Torr Scientific.

What are the uses of Brewster windows?

The main purpose of Brewster windows is for minimising the reflections of p‑polarised light, partially linearly polarising the light within laser cavity setups.

This window transmits as efficiently as our zero-length viewports with antireflective coatings for tailored wavelengths, however the Brewster window can transmit at this level without requiring any coating procedures.

What options are available for Brewster windows?

We do not currently have a standard product we manufacture for Brewster windows.

Each part of the assembly is down to the customer’s requirements.

You can find an example of a custom-designed Brewster windows featuring a demountable fused silica optic here.

Customisable options include:

Optic materials and customisation

Torr Scientific offers a wide range of optical materials for use with our Brewster windows. Other options include O-ring or bonded seals. The advantage of the O-ring seal is that the optic can be removed for replacement or cleaning. 

You can view all our optical materials (for both Brewster windows and standard viewports), on our viewports webpage along with descriptions for each of their features and specialities.

The choice of optic impacts the Brewster angle due to each optical material having a different refractive index.

How do Brewster windows work?

To understand how Brewster windows work we need to discuss the structure of light and refractive indices.

The structure of light

Light can be visualised as having two components

• S-polarised waves oscillating up and down and
• P-polarised waves oscillating side to side

This is called linear polarisation.

When firing a beam of light through a Brewster window the s‑polarised light is reflected and p‑polarised light is transmitted.

This is thanks to the “Brewster” angle.

The Brewster angle & the level of reflectance

Brewster windows reflect one polarisation of light and transmit the other, due to the relationship between the angle of the beam striking the surface and the refractive index.

That relationship is called the “level of reflectance”.

This is different for each of the polarised beams, but importantly:

• It can equal zero for the p-polarised beam.
• It cannot equal zero for the s-polarised beam.

Therefore, with knowing the level of reflectance and the refractive index of the material, we can use this information to calculate what we need for the angle of the beam.

This is called the Brewster angle.

For more information, read our article on Brewster window theory.

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