Physics Department

A totally optical atomic clock


We're all locked in time, as we speed from appointment to appointment, whether we're aware of it or not. The accurate measurement of time is crucial--not only for meeting friends on time, but also for docking space shuttles spinning around the earth. It's vital for planning global transportation and for locating ships lost at sea.

Physicist Scott Diddams, a 1989 Bethel alumnus, and his research team at the National Institute of Standards and Technology (NIST) in Boulder, Colo., are developing a totally optical atomic clock--the most accurate clock to date the "ticks" one million billion times per second. This effort has surely caught the attention of the scientific world. During the summer of 2001, National Geographic, Science Journal, Nature ABC News, The New York Times, and other media covered this scientific leap to an astronomical new level of accuracy.

Some of the first clocks ever invented ran with a pendulum, like a grandfather clock. The swinging pendulum ticked, and gears moved the hands on the face of the clock. But those ancient clocks lost many seconds a month. Improvements were made to mechanical clocks over the years, but scientists have continually searched for more accurate method for measuring time. Quartz timepieces were a major scientific advancement in measuring time. These clocks digitally counted the oscillations of a quartz crystal instead of the swings of a pendulum and were therefore far more accurate than any mechanical clock.

Next came atomic clocks with a new constant by which to synchronize the clock--the constant rate of oscillation of a particular atom.

An old-fashioned grandfather clock might tick once a second, while a cesium atom vibrates more than nine billion times per second. Scientists therefore chose cesium atoms to begin a new way of measuring time. The cesium atomic clock defines "one second" as the time it takes a cesium atom to vibrate 9,192,631,770 times. The oscillations of the cesium atoms were counted by a microwave counter. Thus, the microwave atomic clock became the official timekeeper for the world.

But the limitation of the cesium microwave atomic clock was the speed of its electronic counter. Enter Scott Diddams. His team has developed an optical counter called a "femtosecond laser," which can count oscillations one million times faster than the cesium microwave clock.

Until Diddams and his team developed their new clock, the most accurate atomic clock was projected to lost a second every 30 million years. The new optical atomic clock may lose a second every 30 billion years!

"The interesting thing about making clocks is that there is no fundamental physical limit to how accurate they can be," said Diddams. "So the challenge is always there to make a better one. That should occupy my time for the near future." He estimates it will take 10 to 20 years to see the practical application of the newer, faster atomic clock. Some postulate that the newest atomic clock will aid in more accurate measurement in deep space exploration.


Nobel Prize wining physicist William D. Phillips, in the Atomic Physics Division of the NIST, calls this optical clock "a major advance in he science and art of timekeeping." Optical clocks are the future of atomic time, he said. "This work represents the realization of a long-standing dream to baste atomic time on an optical frequency making a laser 'tick' with incredible clock-like stability."

Diddams got his start in physics at Bethel, receiving an education he says has served him well. "I've been very pleased with the education I received at Bethel. In addition to excellent training in physics, the liberal arts background has served me well. The ability to think broadly, write, and communicate well are valuable skills in any field," he says.

Bethel Professor Richard Peterson, an award-winning physicist himself, had the greatest influence on Diddams during his Bethel career. "He's truly a remarkable instructor and the reason I became interested in physics in the first place," Diddams adds. Following Bethel, Diddams earned a Ph.D. in optical physics from the University of New Mexico, and did postdoctoral work in Boulder, Colo., where he now lives with Naomi Heiser, his wife, and their 2-year-old son, Ariel.

Richard Peterson, BethelĀ  Physics professor, responds:

Scott Diddams is most remembered for a distinct warmth and empathy for his fellow students and the faculty while he was a student at Bethel. No student in the last two decades of our program has been more liked and respected. In addition, during his student days he was particularly interested in missions work in Brazil, so he learned some Portuguese on the side to further his interactions there.

Scott has been a pacesetter at the postdoctoral level (beyond the Ph.D.). He was the first of our physics majors to be appointed as a coveted National Research Council (NRC) Postdoctoral Fellow. We since have had two or more applications for NRC Postdocs, including recent winner Jason Jones '94, who also received his Ph.D. from the University of New Mexico, and strong candidate Chad Hoyt, another 1994 Bethel graduate who is completing a Ph.D. in physics and optical science and awaiting word on his NRC application of January 2002.

During a summer physics conference in the Denver area in 1997, Scott showed me around his postdoctoral research area at the University of Colorado in Boulder. I most enjoyed the detailed introduction to his extraordinary work with femtosecond lasers while touring his own lab. Across the hall from his lab he also took me to visit the Carl Wieman and Eric Cornell lab that had just achieved the first Bose-Einstein condensation in the previous year (winning the 2001 Nobel Prize for that accomplishment).

Scott went through Bethel's physics program with a spectacular group of students who graduated in '88 and '89. Four students earned Ph.D.s from the University of Minnesota, MIT, and Carnegie-Mellon University. He began Bethel's track record of very strong students participating in the Ph.D. Optical Science Physics program at the University of New Mexico. This program is one of the best in optical physics in the United States. I am excited to say that the University of New Mexico recently has offered to send one of its Ph.D. graduates to visit Bethel this year to personally interview more of our graduates.

Note: drawing taken from