Vacuum Optical Ports for use with Compression Fittings

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A GC05WP Wedged Optical Port Secured in a KF25C050 Vacuum Flange

Features

• Couple Beams Into and Out of Vacuum Systems
• Transmission over Broad Wavelength Ranges:
  • UV Fused Silica Window: 185 nm - 2.1 µm
  • Sapphire Window: 200 nm - 4.5 µm
• Suitable for Vacuum Pressures as Low as 10^-7 Torr at 25°C
• Compatible with Our KF25 and KF16 Flange to Compression Fitting Adapters for Ø1/2" (Ø12.7 mm) Pipes and Tubes
• Custom Fused Silica or Sapphire Optical Ports Available by Contacting Tech Sales

Thorlabs' Optical Ports provide a solution for coupling beams into or observing processes inside of a vacuum chamber. The GC05BP optical port consists of a UV fused silica Brewster window fused to a Ø1/2" fused silica tube at its designed Brewster's angle of 55.5°, enabling it to transmit the p-polarized component of light with near-zero reflection losses. We also offer two optical ports with windows that have a 30 arcmin wedge to eliminate fringe patterns and reduce etalon effects: a UV fused silica window fused to a fused silica tube (Item # GC05WP) or a sapphire window fused to an alumina tube (Item # GC05SP).

UV fused silica (UVFS) is a durable material that resists chipping and cracking and offers high transmission for wavelengths between 185 nm and 2.1 μm. Sapphire is a chemically inert material with exceptional surface hardness that offers high transmission for wavelengths between 150 nm and 4.5 μm, ideal for use in IR systems.

All ports sold below have been tested using vacuum and Helium leak testing to ensure that they are capable of withstanding vacuum environments as low as 10^-7 Torr and pressures as high as 5 psi at 25 °C. Post production, the ports undergo ultrasonic cleaning, a methanol rinse, and are coated with First Contact™^* Polymer, a polymer coating that protects the optic from scratching and chipping and can be easily peeled off before the optical port is used. The ports are not vacuum sealed when shipped; before using the ports in a vacuum setup, we advise users to clean with a methanol rinse.

The outer diameter of these ports is Ø1/2" (Ø12.7 mm), allowing them to be integrated into KF16 and KF25 vacuum systems using the KF16C050 and KF25C050 flange to compression fitting adapters, respectively. A rib circles the ports and ensures that there is no movement under vacuum when the ports are installed in compression fittings. 

For custom optical ports, including alternative windows and coatings, please contact Tech Sales.

*First Contact is a trademark of Photonic Cleaning Technologies, LLC.

Optical Transmission

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Transmission of 10 mm Thick, Uncoated UV Fused Silica Window

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Transmission of 5 mm Thick, Uncoated Sapphire Window

UV Fused Silica Index of Refraction and Brewster's Angle

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This graph shows the calculated reflectance of uncoated UV fused silica for polarized light as a function of angle of incidence. The reflectance for P-polarized light goes to zero at Brewster's angle.

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This graph shows the calculated index of refraction of UV fused silica as a function of wavelength.

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This graph shows the calculated value of Brewster's angle as a function of wavelength when light is passing from air to UV fused silica.

The index of refraction for UV fused silica is wavelength dependent, as shown in the graph above, and expressed by the following formula:

.

Please note that that the wavelength needs to be in microns when using the formula above. Brewster's angle is given by

.

Here, θ_B is Brewster's angle, n_i is the index of refraction of the incident medium (1.0003 for air), and n_t is the index of refraction of the transmitting medium (1.45701 for fused silica at 633 nm). Hence, Brewster's angle also displays a wavelength dependence, as shown in the plot above.

The image above shows the reflection of S-polarized light and transmission of P-polarized light through a Brewster window. Some S-polarized light will be transmitted through the window.

Brewster Windows

Brewster windows are typically used as polarizers within laser cavities. When positioned at Brewster's angle (55° 32' at 633 nm), the P-polarized portion of the light will pass through the window with no losses, while a fraction of the S-polarized portion will be reflected off the Brewster window. When used in a laser cavity, the Brewster window essentially acts as a polarizer.

Brewster's angle is given by

θ_B is Brewster's angle.
n_i is the index of refraction of the incident medium, which is 1.0003 for air.
n_t is the index of refraction of the transmitting medium, which is 1.45701 for fused silica at 633 nm

It should be noted that the index of refraction is wavelength dependent. For fused silica, the index of refraction can be expressed as

.

Please note that that the wavelength needs to be in microns when using the formula above.