Increased spontaneous emission
Increased spontaneous emission , also superluminescence or super radiation or English amplified spontaneous emission , ASE for short is light generated by spontaneous emission , which was optically amplified by stimulated emission in rod-shaped media with population inversion in the direction of the rod axis . The population inversion is usually generated by optical pumping . The effect occurs in laser media and optical amplifiers . The ASE can propagate in both directions of the resonator axis.
Depending on the application, the increased spontaneous emission may or may not be desired.
In the case of a super-emitter , the preliminary stage of a laser, the effect is desirable and leads to simple structures without a laser resonator . In general, the effect is necessary for self-oscillating lasers. The feedback of the superluminescence in the laser resonator leads to laser activity when the laser threshold is exceeded.
The increased spontaneous emission causes noise in optical amplifiers and thus limits the transmission speed in optical fibers . In extreme cases it can lead to the self-destruction of an optical amplifier, or at least it limits the maximum stage gain.
With the disk laser, the effect limits the performance. With Q-switched lasers , the effect leads to a loss of power, since emission stimulated by spontaneous photons occurs even when the Q- switch is blocked and the inversion is already partially broken down before the Q-switch opens.
In high-performance CPA lasers with peak outputs from a few terawatts to petawatts, such as the POLARIS laser system, for example , the increased spontaneous emission limits the temporal intensity contrast. Due to the compression of the laser pulses stretched during the amplification, the amplified spontaneous emission causes a significantly longer pulse, some of which is before the actual laser pulse. Due to the high intensities in the focus of up to 10 ^ 22 W / cm², the ASE is often sufficient to significantly disrupt or even prevent the desired laser-target interaction.
See also
Self-amplified spontaneous emission , a corresponding operating mode of free-electron lasers
Individual evidence
- ↑ a b Jürgen Eichler , Hans Joachim Eichler : Laser: Basics · Systems · Applications , Springer-Verlag , 2013, ISBN 978-3-662-22080-1 , p. 36 [1]
- ↑ a b Andres Keller: Broadband cables and access networks: Technical principles and standards , Springer-Verlag , 2011, ISBN 978-3-642-17631-9 , p. 172 [2]
- ↑ Henning Fouckhardt : Photonics: An introduction to integrated optoelectronics and technical optics , Springer-Verlag , 2013, ISBN 978-3-322-94734-5 , p. 200 [3]
- ↑ Marc Eichhorn: Laserphysics: Fundamentals and Applications for Physicists, Mechanical Engineers and Engineers , Springer-Verlag , 2012, ISBN 978-3-642-32648-6 , p. 175 [4]
- ↑ Sebastian Keppler, Alexander Sävert, Jörg Körner, Marco Hornung, Hartmut Liebetrau: The generation of amplified spontaneous emission in high-power CPA laser systems . In: Laser & Photonics Reviews . tape 10 , no. 2 , March 1, 2016, ISSN 1863-8899 , p. 264-277 , doi : 10.1002 / lpor.201500186 , PMID 27134684 , PMC 4845653 (free full text) - ( wiley.com [accessed September 11, 2016]).