4
Conclusion: In summary, we propose a new subnatural
linewidth spectroscopy technique, which is a laser by us-
ing Ramsey seperated-ﬁeld cavity to realize the output of
stimulated-emission radiation via multiple coherent interac-
tion with atomic beam. We ﬁnd the linewidth of Ramsey laser
is subnatural if we choose an appropriate atomic level, and the
bad-cavity laser mechanism will dramatically reduce cavit y-
related noise as discussed in active optical clock [15–19]. Our
results show that this new subnatural linewidth spectrosco py
is superior to conventional optical Ramsey seperated-ﬁeld
spectroscopy and any other available subnatural spectrosc opy
technique at present [3–10]. Considering one have to ap-
ply the separated-ﬁeld method in any phase detection as in
Ramsey-Borde´interferometer [2], to investigate the e ﬀects of
phase di ﬀerences between the two oscillating ﬁelds [31] in
this stimulated separated-ﬁeld method with such subnatura l
linewidth will be our next research aim.
We acknowledge Yiqiu Wang and Deshui Y u for fruitful
discussions. This work is supported by MOST of China
(grant 2005CB724500, National Natural Science Foundation
of China (grant 60837004, 10874009), National Hi-Tech Re-
search and Development (863) Program.
∗ E-mail: jbchen@pku.edu.cn
† E-mail: hongguo@pku.edu.cn.
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