A new way to measure nearly nothing: Ultracold trapped atoms to measure pressure

phys.org | 10/20/2018 | Staff
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Many semiconductor fabricators and research labs are under increasing pressure from, of all things, vacuum. These facilities need to remove greater amounts of gas molecules and particles from their setups as new technologies and processes demand lower and lower pressures. For example, the vacuum chambers in which microchip manufacturers lay down a series of ultrathin layers of chemicals step by step—a process that must be utterly free of contaminants—operate at about one hundred-billionth of the air pressure at sea level. Some applications need pressures at least a thousand times lower than that, approaching the even more rarefied environments of the Moon and outer space.

Measuring and controlling vacuum at those levels is an exacting business in which accuracy is essential. Current technology usually relies on a device called an ion gauge. However, ion gauges require periodic recalibration and are not compatible with the new worldwide effort to base the International System of Units (SI) on fundamental, invariant constants and quantum phenomena.

NIST - Scientists - Vacuum - Gauge - Vacuum

Now NIST scientists have designed a vacuum gauge that is small enough to deploy in commonly used vacuum chambers. It also meets Quantum SI criteria, meaning it requires no calibration, depends on fundamental constants of nature, reports the correct quantity or none at all, and has specified uncertainties that are suitable for its application. The new gauge tracks changes in the number of cold lithium atoms trapped by a laser and magnetic fields within the vacuum. The trapped atoms fluoresce as a result of the laser light.

Every time a cold atom is struck by one of the few molecules moving around in the vacuum chamber, the collision kicks the lithium atom out of the trap, decreasing the amount of fluorescent light emitted. A camera records the dimming. The faster the light dims, the more molecules are in the vacuum chamber, making...
(Excerpt) Read more at: phys.org
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