On the ''excess spontaneous emission factor'' in gainguided laser amplifiers
Petermann computed an ''excess spontaneous emission factor'' for gain-guided laser. In this paper, the authors investigate further the role of this factor. Such a factor also appears in the treatment of thermodynamic equilibrium in an attenuating medium-a seeming paradox. Further investigation shows that the excess spontaneous emission excitation at thermal equilibrium is cancelled by the excitations in the other modes which are correlated with that in the fundamental mode. In a medium with gain, cancellation also occurs in a short amplifier in which there is no gain discrimination among modes. The ''excess spontaneous emission factor'' is fully present only in a system in which the different higher order modes have an appreciably smaller gain than the lowest order mode, a high gain amplifier. An analysis of the signal-tonoise ratio of a high gain amplifier reveals that the excess noise factor can be fully compensated by proper input excitation by a lens arrangement. The lens arrangement provides the signal with an ''excess gain'' factor. An ''excess gain'' factor is also present when a thermal source is used.
- Research Organization:
- Bell Communications Research, Holmdel, NJ 07733
- OSTI ID:
- 5443142
- Journal Information:
- IEEE J. Quant. Electron.; (United States), Vol. QE-21:1
- Country of Publication:
- United States
- Language:
- English
Similar Records
Excess spontaneous emission in non-Hermitian optical systems. II. Laser oscillators
Excess noise in gain-guided amplifiers