Westergaard Philip G, Christensen Bjarke T R, Tieri David, Matin Rastin, Cooper John, Holland Murray, Ye Jun, Thomsen Jan W
Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen, Denmark.
Danish Fundamental Metrology, Matematiktorvet 307, 1 sal, 2800 Kongens Lyngby, Denmark.
Phys Rev Lett. 2015 Mar 6;114(9):093002. doi: 10.1103/PhysRevLett.114.093002. Epub 2015 Mar 4.
As an alternative to state-of-the-art laser frequency stabilization using ultrastable cavities, it has been proposed to exploit the nonlinear effects from coupling of atoms with a narrow transition to an optical cavity. Here, we have constructed such a system and observed nonlinear phase shifts of a narrow optical line by a strong coupling of a sample of strontium-88 atoms to an optical cavity. The sample temperature of a few mK provides a domain where the Doppler energy scale is several orders of magnitude larger than the narrow linewidth of the optical transition. This makes the system sensitive to velocity dependent multiphoton scattering events (Dopplerons) that affect the cavity field transmission and phase. By varying the number of atoms and the intracavity power, we systematically study this nonlinear phase signature which displays roughly the same features as for much lower temperature samples. This demonstration in a relatively simple system opens new possibilities for alternative routes to laser stabilization at the sub-100 mHz level and superradiant laser sources involving narrow-line atoms. The understanding of relevant motional effects obtained here has direct implications for other atomic clocks when used in relation to ultranarrow clock transitions.
作为使用超稳腔进行最先进激光频率稳定的替代方案，有人提出利用原子与窄跃迁耦合到光学腔时产生的非线性效应。在此，我们构建了这样一个系统，并通过将88锶原子样本与光学腔强耦合，观测到了窄光学线的非线性相移。几毫开尔文的样本温度提供了一个区域，其中多普勒能量尺度比光学跃迁的窄线宽大几个数量级。这使得系统对影响腔场传输和相位的速度依赖多光子散射事件（多普勒子）敏感。通过改变原子数量和腔内功率，我们系统地研究了这种非线性相位特征，其显示出与温度低得多的样本大致相同的特征。在一个相对简单的系统中的这一演示为在低于100毫赫兹水平实现激光稳定的替代途径以及涉及窄线原子的超辐射激光源开辟了新的可能性。在此获得的对相关运动效应的理解对于其他原子钟在与超窄时钟跃迁相关使用时具有直接影响。
