arXiv quant-ph/99030821999-03-25quant-ph

激光线宽的量子极限

The ultimate quantum limit to the linewidth of lasers

H. M. Wiseman

备注：: 10 pages of text plus one figure

摘要：

激光器的线宽的标准量子极限是$\ell_{0}=κ/2\bar{n}$，对于该激光器，增益介质可以被消除。这里，$κ$是强度阻尼率，而$\bar{n}$是平均光子数。这包含了来自损耗和增益过程的相等贡献，因此将线宽完全归因于来自自发增益的相位噪声的简单论点是错误的。我表明，{ \em未受激}增益过程实际上不会引入相位噪声，因此激光线宽的最终量子极限仅来自损耗，等于$\ell_{ult}= κ/4\bar{n}$。我调查了一些物理增益机制，试图实现增益没有相位噪声：一个线性的原子场耦合有限的相互作用时间;一个非线性的原子场耦合;和绝热光子转移使用一个违反直觉的脉冲序列。第一种最多达到标准极限$\ell_{0}$，第二种达到$3/4 \ell_{0}$，而第三种达到$\ell_{ult} = 1/2 \ell_{0}$的极限。

英文摘要：

The standard quantum limit to the linewidth of a laser for which the gain medium can be adiabatically eliminated is $\ell_{0}=κ/2\bar{n}$. Here $κ$ is the intensity damping rate and $\bar{n}$ the mean photon number. This contains equal contributions from the loss and gain processes, so that simple arguments which attribute the linewidth wholly to phase noise from spontaneous gain are wrong. I show that an {\em unstimulated} gain process actually introduces no phase noise, so that the ultimate quantum limit to the laser linewidth comes from the loss alone and is equal to $\ell_{ult}= κ/4\bar{n}$. I investigate a number of physical gain mechanisms which attempt to achieve gain without phase noise: a linear atom-field coupling with finite interaction time; a nonlinear atom-field coupling; and adiabatic photon transfer using a counterintuitive pulse sequence. The first at best reaches the standard limit $\ell_{0}$, the second reaches $3/4 \ell_{0}$, while the third reaches the ultimate limit of $\ell_{ult} = 1/2 \ell_{0}$.

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英文摘要：

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