The development of active optical clock

Abstract

The atomic clocks, whether operating at optical or microwave region, can be divided into two categories according to their working mode, namely the passive clocks and active clocks. The passive clocks, whose standard frequency is locked to an ultra-narrow atomic spectral line, such as laser cooled Cs beam or lattice trapped Sr atoms, depend on the spontaneous emission line. On the contrary, the active clocks, in which the atoms are used as the gain medium, are based on the stimulated emission radiation, their spectrum can be directly used as the frequency standard. Up to now, the active hydrogen maser has been the most stable microwave atomic clocks. Also, the Sr superradiant active atomic clock is prospects for a millihertz-linewidth laser. Moreover, the optical clocks are expected to surpass the performance of microwave clocks both in stability and uncertainty, since their higher working frequency. The active optical clock has the potential to improve the stability of the best clocks by 2 orders of magnitude. In this work, we introduce the development of active optical clocks, and their types is classified according to the energy-level structure of atoms for stimulated radiation.

A new scheme of fully stabilized soliton microcombs

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Development of Compact and Robust Physical System for Strontium Optical Lattice Clock

“…In recent years, there has been significant improvement in the stability and uncertainty of optical clocks, surpassing the performance of the current reference clock, i.e., the cesium microwave clock. Optical clocks demonstrate potential as the most promising candidate for the future redefinition of the second, based on optical transitions [1][2][3][4][5][6][7][8][9][10]. These clocks have found wide application in fundamental physics research.…”