The fiber-based amplification of narrow-band continuous radiation is limited by non-linear effects such as stimulated Brillouin scattering (SBS). Alternative laser sources which do not display this limitation are investigated at Fraunhofer IOF.
If population inversion is generated in an actively doped fiber with suitable pumping and if this fiber is used neither in an amplification nor a laser configuration, in accordance with its amplification profile it spontaneously emits so-called amplified spontaneous emission (ASE).
The broadband cw-laser sources are always used when the application simultaneously requires a high spatial coherence but low temporal coherence. With a suitable design, very high power can be generated in a fiber-based system. However, it is also possible to spectrally shape these ASE sources and thus adapt them to specific applications. It is thus possible to realize customized temporal coherences as well as enable the amplification of narrow-band sources in the kW range without SBS.
At Fraunhofer IOF, innovative continuous laser sources are developed and characterized using Fabry-Perot and radio frequency spectrometers, phase jitter and coherence measurement.
O. Schmidt, M. Rekas, C. Wirth, J. Rothhardt, S. Rhein, A. Kliner, M. Strecker, T. Schreiber, J. Limpert, R. Eberhardt, and A. Tünnermann, »High power narrow-band fiber-based ASE source«, Opt. Express 19, 4421-4427 (2011).