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Calcium Thermal Beam Optical Clock


A simple, compact alternative to the highest performing optical standards, the Ca clock uses a thermal beam of neutral atoms with one or two lasers to achieve high stability in a potentially field-able instrument.





This research follows up on work first begun on the 657 nm intercombination line in neutral calcium (natural linewidth = 375 Hz) by Barger and Bergquist at NIST in 1979. Using a four-beam optical Ramsey technique we perform high resolution spectroscopy on calcium atoms in a thermal beam with a pre-stabilized probe laser. We then stabilize the frequency of the probe laser to the atomic resonance to yield a stable optical frequency. Thanks in part to state-of-the-art optical cavities, we have used this system to achieve stabilities 1-2 orders of magnitude better than those of hydrogen masers for time scales up to several hundred seconds. Previous versions of the Ca standard in our laboratory used magneto-optic traps to generate samples of laser-cooled atoms that demonstrated one-second fractional-frequency instabilities of 4 x 10-15 and an absolute fractional frequency uncertainty of 7.5 x 10-15. More recently we have found that we can achieve a similar instability with a much simpler, thermal beam-based system, albeit with increased uncertainty. As a result, one can envision a compact, single-laser system that could achieve an instability approaching 1 Hz in 1 s. When combined with a femtosecond frequency comb, such calcium clocks could find application in a variety of precision timing applications.

Future research will include: (1) the addition of a blue detection laser to the system in order to improve the clock stability by up to an order of magnitude or more, especially on timescales of seconds and below; (2) evaluating potential shifts and optimizing the performance of the beam clock on longer timescales, for hours or days.

Major Accomplishments:

  • Developed and demonstrated 5 x 10-15 fractional instability at 1 s for a single laser, thermal atomic beam system. Demonstrated 8 x 10-16 fractional instability at 1 s for a two-laser, thermal atomic beam system.
  • Achieved a resolution near 1 kHz (line Q ~ 5 x 1011) with a thermal beam system.

NRC Postdoc Program

Apply for an NRC postdoc in optical atomic clock or fs-laser frequency comb research. Application deadlines are February 1 and August 1 annually (but inquire well in advance).

Summer Undergraduate Research Fellowship (SURF)

Summer program at NIST-Boulder for undergraduates in science, engineering, and mathematics. The application deadline is February 15 annually.

Postdoctoral, Visiting Scientist, and Graduate Positions

Our Group has periodic openings for Postdoctoral Fellows, Visiting Scientists, and Graduate Students. Please contact us for more information.


End Date:


Lead Organizational Unit:

Richard Fox 303-497-3478
Andrew Ludlow 303-497-4972
Chris Oates 303-497-7654
Judith Olson 303-497-3167