|Abstract : || |
Satellite based navigation is an example of a few contemporary applications that have revolutionised our daily lives. Today, no matter where we are on the earth, thanks to the satellite constellation of the GPS (Global Positioning System) we never have to worry about two things – our precise location and the time. GPS is used globally for myriads of applications ranging from surveying, road transport, aviation, agriculture and telecommunications and so on. Currently, the Indian Space Research Organisation (ISRO) is developing the Indian Regional Navigation Satellite System (IRNSS), nicknamed NavIC, which is a satellite navigation system similar to the GPS. While the names such as GPS and NavIC are very familiar to most of us due their extensive applications in our daily lives, the basic principles underlying these systems are not well known to many. Even less well known is the fact that at the heart of any satellite navigation system are extremely precise atomic clocks which are synchronised with each other to better than a few billionths of a second or a few nanoseconds.
In this talk we shall mainly discuss the basic principles of operation of an atomic clock. The basis of an atomic clock is an atomic resonance which is a truly fundamental and invariant quantity. In the practical implementation a quartz oscillator is phase locked to the atomic resonance to give a usable output. We shall discuss recent developments in this field that have resulted in clock accuracies better than a part in 10^15. In simple terms, such a clock would lose or gain 1 sec in about 3 million years