A New Way To Measure Extremely Low Pressures

  • New cold-atom vacuum standard can accurately measure low-pressure levels. 
  • Researchers are currently testing individual modules and a working prototype will be available soon. 
  • It will be the first absolute sensor to operate in ultrahigh and extreme-high vacuum.

There are many methods to measure pressure/vacuum. Several research labs are using new technologies to remove a large number of particle and gas molecules to create and measure lower pressures.

Many processes require extremely low pressure to operate optimally, for instance, microchip manufacturers work in vacuum chambers that have nearly 100 billion times low pressure than air pressure at sea level. In fact, a few applications require thousands of times lower pressure than that, which is similar to the Moon and outer space environments.

At such levels, the process of controlling and measuring pressure becomes very challenging. Existing methods rely on an instrument known as ion gauge, but it cannot deal with invariant parameters and quantum phenomena.

Now, researchers at the National Institute of Standards and Technology developed a vacuum gauge that can be deployed in conventional vacuum chambers. Since it does not require any calibration and relies on fundamental constants of nature, it is suitable for quantum information science.

How It Measures Lower Pressure Levels?

The new device monitors changes in the number of lithium atoms trapped by magnetic fields and a laser inside the vacuum. These trapped atoms fluoresce, and when they get struck by other particles in the vacuum, the amount of fluorescent light decreases. The pressure can be detected by observing the fluctuations in fluorescence levels.

Let us elaborate this concept in details: the researchers designed a cold-atom vacuum standard (CAVS) to measure fundamental properties of atoms. The system is small enough (as well as portable) to be used in current vacuum chambers.

The concept of Portable CAVS | Credit: NIST

It relies on the magneto-optical trap that uses a total of 6 laser beams (each of 3 axes has 2 opposing beams). The speed of trapped atoms decreases as they absorb energy from laser photons. To keep atoms in a particular position, the magneto-optical trap uses a varying magnetic field, whose strength reduces with distance inward (zero at the center). Thus, all atoms are pushed toward the center.

Reference: IOPScience | doi:10.1088/1681-7575/aadbe4 | NIST

They used only one laser beam directed onto an optical instrument called a diffraction grating. The instrument divides the light into several beams coming from different angles, creating a trap. At this point, lithium atoms are slightly above absolute zero and struck by surrounding hydrogen molecules.

Credit: NIST

The following are the reasons why they preferred lithium atoms instead of cesium and rubidium:

  1. Lithium is relatively easy to cool and trap.
  2. It’s a much better sensor for vacuum.
  3. Interaction between hydrogen molecules and lithium atoms can be accurately measured.
  4. At room temperature, lithium has a low vapor pressure, which prevents it from converting into a gaseous state.

What’s Next?

At present, researchers are testing individual modules and they are expecting a working prototype in the near future. It will be the first absolute sensor to operate in ultrahigh and extreme-high vacuum, which are an important part of the infrastructure in advanced research, from quantum information science to gravitational-wave detectors.

Read: Photonic Fibers Change Color When Stretched | To Show Pressure Level

This portable system will allow manufacturers and scientists to precisely measure the level of vacuum before the process or experiment starts. Lower vacuum levels can be accurately evaluated – levels whose importance is continuously increasing in fields like quantum science.

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