Friday, June 21, 2013

Laser Pulses Create More Accurate Atomic Clocks

Date: 14 June 2013 Time: 02:21 PM ET

Time Illusion Stock Images - Is Time Real?
Keeping extremely precise time is key to many modern technologies, from GPS to mobile phone networks and broadcasters' transmitters. That's where optical atomic clocks, which are about 100 times more precise than microwave-based atomic clocks, come in.
CREDIT: Shutterstock/Kim D. French
Updated on Saturday, June 15, at 3:38 p.m. ET.

The ultimate accessory in exact timekeeping — the atomic clock — is set to become even more precise, after ultrashort laser pulses were successfully transmitted across open air to help synchronize the "ticking" of new optical atomic clocks.

Keeping extremely precise time is not just a question of scientific achievement. It is a key to many modern technologies, from Global Positioning Systems (GPS) to mobile phone networks and broadcasters' transmitters. For GPS systems, an error of just one nanosecond, or a billionth of a second, would mean the location is about 12 inches (30 centimeters) off.

To ensure maximum precision, the U.S. national time standard is determined by atomic clocks. Current ones use extremely cold cesium atoms, laser-cooled to temperatures close to absolute zero. The cesium atoms are then blasted with microwaves until the atoms vibrate at a certain frequency. That frequency is equal to the energy that gets absorbed when the microwave radiation causes the cesium atom's outermost electron to jump to a higher orbit, or 9,192,631,770 Hz. What we call "the second" is then derived from the duration of 9,192,631,770 periods of this frequency.

Now physicists are developing new optical atomic clocks which could be about 100 times more precise than microwave-based ones. They operate in a similar manner, but use laser light instead of microwaves. Laser light has a much higher frequency and hence gives much better timing resolution and much faster transmission of data.

In the future, optical atomic clocks could be used for satellite-based experiments to prove Einstein's theory of general relativity and create more precise GPS satellite navigation systems, which "could be improved in the sense that you could put better optical clocks in satellites and crosslink them optically," Newbury said.

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