### Abstract

Original language | Undefined |
---|---|

Title of host publication | Proceedings Doctoral Students Conference on Optics |

Place of Publication | Jena, Germany |

Publisher | Abbe School of Photonics, Universitat Jena |

Pages | Page 8 |

Number of pages | 1 |

ISBN (Print) | not assigned |

Publication status | Published - Oct 2013 |

### Publication series

Name | |
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Publisher | Abbe School of Photonics, Universität Jena |

### Keywords

- IOMS-APD: Active Photonic Devices
- IR-88769
- METIS-302640
- EWI-24305

### Cite this

*Proceedings Doctoral Students Conference on Optics*(pp. Page 8). Jena, Germany: Abbe School of Photonics, Universitat Jena.

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*Proceedings Doctoral Students Conference on Optics.*Abbe School of Photonics, Universitat Jena, Jena, Germany, pp. Page 8.

**A fresh look at continuous-wave lasers: How they really work!** / Pollnau, Markus.

Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › Academic

TY - GEN

T1 - A fresh look at continuous-wave lasers: How they really work!

AU - Pollnau, Markus

N1 - eemcs-eprint-24305

PY - 2013/10

Y1 - 2013/10

N2 - This lecture describes the operation principle of a continuous-wave (cw) laser. In order to keep the photon rate equation and its solution simple, usually the spontaneous-emission rate is neglected with the argument that it is so much smaller than the stimulated-emission rate. The direct consequence is that in a cw laser the gain would equal the losses. Yet, additional implications are that the light emitted by such a laser would be a pure sine wave with an infinite coherence length, its linewidth would become a delta function, its Q-factor would assume an infinite value, the coherent photon number would build up and coherence would manifest itself inside the resonator only when pumping above the laser threshold, and the threshold inversion would depend only on the total resonator losses. None of these implications holds true for any laser that mankind has ever created. Starting from vacuum fluctuations, we consider spontaneous emission directly in the photon rate equation, thereby a priori avoiding all these inconsistencies. It is then straight-forward to see that in a cw laser the gain is smaller than the losses, a cw laser does not only have a finite linewidth that can be derived in a very simple manner, but also a finite Q-factor, as well as two laser thresholds which are both different from the commonly assumed “threshold inversion‿. This work was performed in collaboration with Dr. Marc Eichhorn from the French-German Research Institute of St. Louis, France.

AB - This lecture describes the operation principle of a continuous-wave (cw) laser. In order to keep the photon rate equation and its solution simple, usually the spontaneous-emission rate is neglected with the argument that it is so much smaller than the stimulated-emission rate. The direct consequence is that in a cw laser the gain would equal the losses. Yet, additional implications are that the light emitted by such a laser would be a pure sine wave with an infinite coherence length, its linewidth would become a delta function, its Q-factor would assume an infinite value, the coherent photon number would build up and coherence would manifest itself inside the resonator only when pumping above the laser threshold, and the threshold inversion would depend only on the total resonator losses. None of these implications holds true for any laser that mankind has ever created. Starting from vacuum fluctuations, we consider spontaneous emission directly in the photon rate equation, thereby a priori avoiding all these inconsistencies. It is then straight-forward to see that in a cw laser the gain is smaller than the losses, a cw laser does not only have a finite linewidth that can be derived in a very simple manner, but also a finite Q-factor, as well as two laser thresholds which are both different from the commonly assumed “threshold inversion‿. This work was performed in collaboration with Dr. Marc Eichhorn from the French-German Research Institute of St. Louis, France.

KW - IOMS-APD: Active Photonic Devices

KW - IR-88769

KW - METIS-302640

KW - EWI-24305

M3 - Conference contribution

SN - not assigned

SP - Page 8

BT - Proceedings Doctoral Students Conference on Optics

PB - Abbe School of Photonics, Universitat Jena

CY - Jena, Germany

ER -