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.

Characterization and suppression of background light shifts in an optical lattice clock



Robert J. Fasano, Yun Jhih Chen, Will McGrew, Wesley J. Brand, Richard W. Fox, Andrew Ludlow


Experiments involving optical traps often require precise control of the ac Stark shifts induced by strong confining light fields. By carefully balancing light shifts between two atomic states of interest, optical traps at the magic wavelength have been especially effective at suppressing deleterious effects stemming from such shifts. Highlighting the power of this technique, optical clocks today exploit Lamb-Dicke confinement in magic- wavelength optical traps, in some cases realizing shift cancellation at the ten parts per billion level. Theory and empirical measurements can be used at varying levels of precision to determine the magic wavelength where shift cancellation occurs. However, lasers exhibit background spectra from amplified spontaneous emission or other lasing modes which can easily complicate measurement of the magic wavelength and its reproducibility in other experiments or conditions. Indeed, residual light shifts from laser background have plagued optical clock measurements for many years. In this work, we develop a simple theoretical model allowing prediction of light shifts from measured background spectra. We demonstrate good agreement between this model and measurements of the background light shift from an amplified diode laser in an Yb optical lattice clock. Additionally, we model and experimentally characterize the filtering effect of a volume Bragg grating bandpass filter, demonstrating that application of the filter can reduce background light shifts from amplified spontaneous emission well below the 10−18 level. This demonstration is corroborated by direct clock comparisons between a filtered amplified diode laser and a filtered titanium:sapphire laser.
Physical Review Applied


amplified spontaneous emission, atomic clocks, lattice Stark shifts, optical lattice clocks


Fasano, R. , Chen, Y. , McGrew, W. , Brand, W. , Fox, R. and Ludlow, A. (2021), Characterization and suppression of background light shifts in an optical lattice clock, Physical Review Applied, [online], (Accessed July 14, 2024)


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

Created April 8, 2021, Updated March 25, 2024