Connecting the Probe to the EPR Bridge

How to connect the Bridge12 QLP to the EPR bridge

A rectangular waveguide port (WR-28) is located at the top of the probe. The waveguide flange is a UG-599/U with 4 tapped holes, screw size #4-40. This waveguide port is used to connect the QLP probe to the EPR spectrometer. The probe waveguide has an integrated vacuum window to seal the probe to the atmosphere, when operating the probe at cryogenic temperatures.


Do not drop any screws or washers into the waveguide port. This could potentially damage the vacuum window located inside the waveguide.

If parts are accidentally dropped into the waveguide, do not use any sharp objects to retrieve the part. Instead, flip the probe over and gently shake the probe to remove the dropped item.

If a part got stuck inside the waveguide and you are not able to retrieve it, do not connect the probe to the spectrometer, and contact Bridge12 at

Connecting the Probe to the Spectrometer


Please make yourself familiar with the instructions below before attempting to install the probe. At no point should you use any force during the installation process. In general, all threads, screws, etc. are imperial size, not metric. Please use the appropriate tools to fasten all screws.

Please follow these steps to connect the probe to the spectrometer:

  1. First time installation: Remove Kapton tape from waveguide flange (for shipping the waveguide port of the probe is protected by a strip of Kapton tape).

  2. Place probe inside cryostat. If you don’t use a cryostat, place probe in the appropriate support structure.

  3. Turn/orient the probe so the waveguide port is located to the left. The waveguide port should be on the side that provides the shortest distance to the EPR bridge. Typically, the EPR bridge is located to the left of the probe.

    To connect the probe to your EPR instrument, the probe comes with additional waveguide components:

    1. WR-28 straight waveguide section, 4 in. length
    2. WR-28 E-bend, 1.5 in.
    3. #4-40 screws, 3/8 in.

    In addition to these parts, please also use the flexible WR-28 waveguide section provided with the EPR instrument to connect the probe to the spectrometer.

  4. Every EPR instrument is slightly different. Here are different scenarios to connect the probe.

    1. Place the E-band on top of the probe, and use the flexible waveguide to connect the probe to the spectrometer.
    2. First add the straight section to the top of the probe and cover the rest of the distance with the flexible waveguide.


When connecting two waveguide sections, always orient the waveguides so that the long section of both waveguides are parallel to each other.

  1. Once the waveguide is connected, connect the temperature sensor to the temperature controller.

What’s next?

Last modified March 28, 2023: Updated QLP and XLP (21b7cb6)