Realization of population inversion between 7S1/2 and 6P3/2 levels of cesium for four-level active optical clock

Lasing and suppressed cavity-pulling effect of Cesium active optical clock

“…What's more, the output power of active optical clock based on a heated cell is expected to be much larger than that based on a thermal atomic beam, for there are far more atoms in the heated glass cell than that in the atomic beam. As pointed previously [39,40,44,45,46,47,48,49], the energy level structure of alkali metals are suitable for four-level active optical clock. For Cs, the relevant atomic energy levels are showed in Fig.…”

“…The bad-cavity collective emission scheme with free-perturbation clock transition as laser medium, is proposed as active optical clock [17,18,19,20,21,23,22,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47]. Population inverted atoms are prepared in a cavity with much wider cavity mode linewidth than clock transition gain bandwidth.…”

“…Since the proposal of active optical clock [18,24], a number of neutral atoms with two-level, three-level, four-level at thermal and laser cooled and trapped configurations, Raman laser, and sequential coupling configuration have been investigated recently [18,19,20,21,23,22,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47]. The potential quantum limited linewidth of the active optical clock [22] is narrower than mHz, and to reach this unprecedented linewidth is possible since the effect of thermal noise on cavity mode can be suppressed dramatically with the mechanism of active optical clock [18,24].…”

“…The detuning between the pumping laser frequency and the transitions related to energy levels of clock transition is thus increased from MHz level in 3-level configuration to THz level in 4level configuration, and the light shift caused by pumping laser can be avoided as the pumpinginduced shift is inversely proportional to the detuning. Active optical clock based on fourlevel quantum system has been investigated [39,40,44,45,46,47,48,49] and the population inversion between 7S 1/2 and 6P 3/2 levels of cesium has been experimentally realized [46] for the lifetime of 7S 1/2 state is longer than that of 6P 3/2 state. In this letter, we experimentally demonstrated the stimulated collective emission behavior and suppressed cavity-pulling effect, the main characteristic of active optical clock with Cs atoms in four-level configuration.…”

Ten years of active optical frequency standards

“…Four-level active optical frequency standards have been proposed to avoid the sensitivity of light shift due to pumping laser [13,14,[25][26][27]. Recently, the lasing action, cavity pulling suppression, and the output linewidth of Cs four-level active optical frequency standards have been investigated experimentally [28][29][30][31].…”