With the needs of social development, the requirements for clock laser pointer accuracy are getting higher and higher, so the quartz clock came into being, it is timed by the stable quartz oscillator inside the quartz clock. With the requirements of scientific and technological development and the persistent pursuit of precision measurement by human beings, quartz clocks gradually cannot meet the requirements and are gradually replaced by clocks with higher accuracy, such as atomic clocks.
Atomic clock uses electromagnetic waves emitted when atoms absorb or release energy to keep time. Because the period of this radiated electromagnetic wave is very stable, coupled with the use of a series of sophisticated instruments for control, the timing of the atomic clock can be very accurate. The first and most commonly used elements in the development of atomic clocks are alkali metals such as hydrogen, cesium and rubidium.
The accuracy of the atomic clock can reach an error of only 1 second every 1 million years. In 1967, the cesium atomic clock was used to define the “second”, that is, 9,192,631,770 times the microwave frequency transition period between the two hyperfine structure sub-levels of the non-interfering 133Cs atom ground state, which is what we usually The International Atomic Time. Since then, the time measurement standard era of atomic “second” has been opened, and the definition of “second” until now is still maintained by the cesium atomic fountain clock.
Pulsar is another unique time measuring instrument. It is a dense neutron star that rotates at a high speed with a very stable rotation period. Through the timing observation of pulsars, a high-precision space-time reference frame can be established. The integrated pulsar time system established and maintained by the pulsar clock may have higher long-term stability than the current atomic time system, and can independently detect the systematic error of the atomic time. This unique time measurement method is being studied by scientists.
For atomic clocks, scientists have spared no effort to explore and have achieved huge research results. They have developed a clock with higher precision than the current reference clock-cesium atomic clock, that is, optical clock. The status of cesium clock as a reference clock has been seriously affected. The research of optical frequency standard has been vigorously developed. This kind of clock, which uses the green laser pointer atomic optical band resonance frequency standard as the time and frequency reference, has greatly improved the accuracy of human time and frequency measurement!