dorsal/arxiv
View SchemaThe ultimate quantum limit to the linewidth of lasers
| Authors | H. M. Wiseman |
|---|---|
| Categories | |
| ArXiv ID | quant-ph/9903082 |
| URL | https://arxiv.org/abs/quant-ph/9903082 |
Abstract
The standard quantum limit to the linewidth of a laser for which the gain medium can be adiabatically eliminated is $\ell_{0}=\kappa/2\bar{n}$. Here $\kappa$ 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 $\ell_{ult}= \kappa/4\bar{n}$. 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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"abstract": "The standard quantum limit to the linewidth of a laser for which the gain\nmedium can be adiabatically eliminated is $\\ell_{0}=\\kappa/2\\bar{n}$. Here\n$\\kappa$ is the intensity damping rate and $\\bar{n}$ the mean photon number.\nThis contains equal contributions from the loss and gain processes, so that\nsimple arguments which attribute the linewidth wholly to phase noise from\nspontaneous gain are wrong. I show that an {\\em unstimulated} gain process\nactually introduces no phase noise, so that the ultimate quantum limit to the\nlaser linewidth comes from the loss alone and is equal to $\\ell_{ult}=\n\\kappa/4\\bar{n}$. I investigate a number of physical gain mechanisms which\nattempt to achieve gain without phase noise: a linear atom-field coupling with\nfinite interaction time; a nonlinear atom-field coupling; and adiabatic photon\ntransfer using a counterintuitive pulse sequence. The first at best reaches the\nstandard limit $\\ell_{0}$, the second reaches $3/4 \\ell_{0}$, while the third\nreaches the ultimate limit of $\\ell_{ult} = 1/2 \\ell_{0}$.",
"arxiv_id": "quant-ph/9903082",
"authors": [
"H. M. Wiseman"
],
"categories": [
"quant-ph"
],
"title": "The ultimate quantum limit to the linewidth of lasers",
"url": "https://arxiv.org/abs/quant-ph/9903082"
},
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