![]() ![]() With these tools in hand, developers began demonstrating impressive performance in optical clocks, which in theory might reach accuracy of 10 -17 to 10 -18. The final step was development of laser femtosecond frequency combs, which can directly measure the absolute optical frequency by dividing the frequency down to the microwave range. Advances in laser stabilization provided the required light source. The development of laser cooling and laser trapping techniques succeeded in slowing and trapping atoms, greatly reducing Doppler shifts and extending interaction times. Building blocks of optical clocksĪlthough the theoretical advantages of optical clocks have long been obvious, realizing that potential has required major innovations in all three fundamental building blocks of optical clocks: an atomic species with a narrow transition in the visible or ultraviolet, a laser with sub-hertz linewidth that can be tuned to match the atomic resonance, and a counter capable of measuring laser frequencies in the optical range.Īchieving high accuracy requires tools to limit the movement of the atoms being studied and holding them in place long enough for the measurement system to achieve high resolution. That’s a big plus for practical measurements. Time averaging improves atomic-clock precision by smoothing out instabilities, but the precision improves only as the square root of the measurement time-so the more stable optical clock needs only a few seconds to reach 10 -15 precision, compared to many hours for a microwave atomic clock. ![]() Optical clocks are also about 100 times more stable than typical cesium clocks, which is a big advantage in achieving precise timing. “It’s like adding five digits to your stop watch,” says Chris Oates, an optical-clock researcher at NIST in Boulder. Their 9.2 GHz microwave frequency was high 50 years ago, but optical frequencies are 100,000 times higher so they can slice time into much smaller intervals. 1īut cesium clocks are coming up against fundamental limits. Lasers cool and confine a fountain of cesium atoms, limiting the clock’s fractional frequency uncertainty to a remarkable 4 × 10 -16, corresponding to a drift of one second in more than 60 million years. Today, the primary time standard is an advanced cesium clock at the National Institute of Standards and Technology (NIST Boulder, CO) called NIST-F1 (see Fig. The first cesium clock in 1955 was accurate to one part in 10 10. Since then researchers have made steady improvements in atomic-clock accuracy. In 1967, metrologists formally defined the second as equal to 9,192,631,770 oscillations of a hyperfine transition of ground-state cesium-133. But the activity plans to further reduce the footprint of the laser system by 50% and increase the average power, so that it can be implemented into portable Strontium-based atomic clocks for use outside of the laboratory environment in a range of quantum technology applications.Atomic clocks based on a microwave transition of cesium have been the gold standard of timekeeping for decades. ![]() The optical clock was demonstrated to a robust and high efficiency performance from a compact footprint. ![]() They found that the latter required too many parts to be operated simultaneously and would be a drain on power, was harder to tune regularly and resulted in a bulkier overall design. The activity chose to use a microchip titanium-sapphire laser cavity design, over a ring laser configuration. In space, optical clocks could be extremely powerful and unique tools in advancing time-keeping, improving the accuracy of navigation and for running fundamental physics experiments with unprecedented precision. There is an increasing need for oscillators with ever higher frequencies and performance, but due to the experimental difficulties of counting optical frequencies, atomic and molecular optical standards have mostly been restricted.Ī new activity with the Technology Development Element (TDE) and Fraunhofer UK developed an optical clock with a laser at 813.428 nanometers by utilising an innovative microchip cavity design with a double laser diode pumping approach. A laser with a frequency stabilised relative to an atomic transition is known as an optical clock and represents a major step forward in the evolution of atomic and frequency standards over the more widely used atomic clocks.įor over half a century atomic frequency and time standards have played an important role in scientific research, precision metrology and technical applications. ![]()
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