Applications of optically pumped atoms

The production of a nonequilibrium distribution of a population of magnetic or HFS sublevels in the ground state has foimd widespread application in high-precision atomic clocks and ultrasensitive magnetometers, and lately in noble-gas-based magnetic imaging. Let us very briefly consider these applications. 

Atomic clocks represent one of the basic applications of atom physics, for the precise measurement of time is one of the most important needs of present-day civilization. The most familiar are atomic clocks using a microwave transition in Cs. In 1967, an international standard was introduced for the second 1 second = 9192631770 cycles of the standard Cs transition. Cesium atomic clocks use the magnetic sorting of sublevels in Cs and the method of spatially separated fields (Ramsey 1987) to 

The next stage in the development of atomic clocks that utilize the control of atoms will be characterized by the use of optical transitions in atoms, specifically laser-cooled trapped atoms or ions, and the laser synthesis of optical and microwave radiation (Chapter 6). 

The measurement of ultraweak magnetic fields is one more area of effective application of optically oriented atoms. Its source lies in an effect studied by Hanle as far back as 1925 in experiments on the fluorescence of Hg vapor in the presence of a magnetic field. When Hg vapor is irradiated with linearly polarized light in resonance 

3 Medical imaging with spin-polarized noble gases 

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