Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

NIST-F3, a cesium fountain frequency reference



Gregory Hoth, Alexander Radnaev, Peter Mitchell, Jeffrey Sherman, Vladislav Gerginov


A cesium fountain frequency reference known as NIST-F3 is under development at the National Institute of Standards and Technology (NIST). The fountain is intended to provide input for the NIST timescale and assist with evaluation of NIST's primary and secondary frequency standards. Here, we describe details of the NIST-F3 apparatus and demonstrate a short-term frequency stability of $2.2\times10^-13}/\sqrt\tau}$ up to averaging times of $2\times10^4$ s. We also present an initial evaluation of the main frequency biases. Due to the particulars of the microwave cavity design employed in NIST-F3, the fountain exhibits a relatively large tilt sensitivity. We measure shifts of order $10^-14}/\mathrmmrad}$ when tilting the fountain. Despite this complication, we show that the tilt sensitivity can be managed with the standard techniques that have been developed for cold-atom fountains. This initial investigation suggests it will be possible to achieve our goal of a fractional frequency stability better than $0.5\times10^-15}$ for up to a few months of averaging time.
Conference Dates
January 23-26, 2023
Conference Location
Long Beach, CA, US
Conference Title
Precise Time and Time Interval Systems and Applications 2023


Hoth, G. , Radnaev, A. , Mitchell, P. , Sherman, J. and Gerginov, V. (2023), NIST-F3, a cesium fountain frequency reference, Precise Time and Time Interval Systems and Applications 2023, Long Beach, CA, US, [online],, (Accessed June 17, 2024)


If you have any questions about this publication or are having problems accessing it, please contact

Created January 24, 2023, Updated June 7, 2024