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Für die Entwicklung neuartiger Gravitationswellendetektoren auf Basis interferometrischer Messungen werden spezielle Hochleistungslaser benötigt. Die Designstudie für das europäische "Einstein Teleskop" offenbarte, dass die optischen Leistungslevel aktuell verwendeter Lasersysteme für die zukünftig angestrebten Spezifikationen nicht mehr ausreichend sind. Die Entwicklung solcher leistungsstarken Lasersysteme ist daher ein weitreichendes Forschungsgebiet und von aktuellem Interesse geprägt. Insbesondere Faserverstärker sind durch ihre exzellente Strahlqualität auch bei höheren Leistungen in den letzten Jahren zunehmend in den Vordergrund gerückt. Die Leistungsskalierung solcher Lasersysteme über aktuelle Limitierungen hinaus ist das Konzept dieser Arbeit. Im Bereich von einfrequenten faserbasierten Lasersystemen stellt dabei der nichtlineare Effekt der stimulierten Brillouin-Streuung die grundlegende Limitierung dar. Insbesondere ist ein signifikantes Rauschen des Lasersystems oberhalb dieser Schwelle messbar. In diesem Zusammenhang wurde das Intensitätsrauschen genauer untersucht. Die Konversion von Phasen- zu Intensitätsrauschen spielt dabei eine entscheidende Rolle. Erstmals konnte die Charakteristik des zusätzlichen breitbandigen Rauschens basierend auf den Parametern eines asymmetrischen Brillouin Verstärkungsspektrums rekonstruiert werden. Die Leistungsskalierung von faserbasierten und einfrequenten Lasersystemen erfolgt beispielsweise durch die Vergrößerung der effektiven Kernfläche. Um die daraus resultierende Minderung der Strahlqualität in Faserverstärkern auszugleichen, wurde das Konzept der "chirally-coupled core" (3C®) Faser entwickelt. Dieser Fasertyp reduziert den Anteil geführter höherer Moden durch zusätzliche um den eigentlichen Kern rotierende Seitenkerne. Im Vergleich zu anderen Spezialfasertypen mit Mikrostrukturen weist diese Faser ein komplettes Glasdesign auf. Die lichtführenden Eigenschaften der 3C®-Faser wurden mit einem speziell entwickelte, High-power lasers are required for the development of novel gravitational wave detectors based on interferometric measurements. The design study for the European ’Einstein Telescope’ revealed that the optical performance of current used laser systems is no longer sufficient for the desired specifications of advanced detector designs. The development of such powerful laser systems is therefore a wide field of research and is of current interest. In particular, fiber amplifiers have increasingly come to the fore in recent years due to their excellent beam quality, even at higher power levels. The power scaling of such laser systems beyond current limitations is the concept of this work. In the area of single-frequency fiber-based laser systems, the non-linear effect of stimulated Brillouin scattering represents the fundamental limitation. In particular, a significant excess noise level of the laser system can be measured above this threshold. In this context, the intensity noise was investigated in more detail. Here, the conversion of phase to intensity noise plays a crucial role. For the first time, the characteristics of the additional broadband noise was reconstructed based on the parameters of an asymmetric Brillouin gain spectrum. The optical output power of fiber-based single-frequency laser systems is scaled, for example, by increasing the effective mode area of the fiber. For the compensation of the resulting reduction of the beam quality in fiber amplifiers, the special concept of the ’chirally-coupled core’ (3C®) fiber was developed. This fiber type reduces the content of guided higher order modes through additional side cores rotating around the actual signal core. Compared to other specialty fiber types with micro-structures inside, this fiber features an all-solid design. The light-guiding properties of the 3C®-fiber were examined with a specially developed S2-setup and the high content of the guided fundamental mode in the fiber core was experimentally c

Integrated fiber components enable compact and robust laser systems but are usually not available with specialty fibers. However, specialty fibers allow power scaling of fiber lasers and amplifiers with all advantages of these fiber designs. In this context, chirally-coupled-core fibers show promising properties for optical fiber components. In this paper, we present the development of a highly-integrated signal and pump combiner in chirally-core-fibers using a side-pumping technology. Combining up to four fiber-coupled pump diodes, a pump-light limited power handling of 600 W can be achieved with an efficiency of 78%. The combiner was tested in a side-pumped single-frequency all-fiber amplifier but can also be implemented in almost any fiber laser or amplifier.

Single-frequency fiber amplifiers in MOPA configuration operating at 1064 nm (Yb3+) and around 1550 nm (Er3+ or Er3+:Yb3+) are promising candidates to fulfill the challenging requirements of laser sources of the next generation of interferometric gravitational wave detectors (GWDs). Most probably, the next generation of GWDs is going to operate not only at 1064 nm but also at 1550 nm to cover a broader range of frequencies in which gravitational waves are detectable. We developed an engineering fiber amplifier prototype at 1064 nm emitting 215 W of linearly-polarized light in the TEM00 mode. The system consists of three modules: the seed source, the pre-amplifier, and the main amplifier. The modular design ensures reliable long-term operation, decreases system complexity and simplifies repairing and maintenance procedures. It also allows for the future integration of upgraded fiber amplifier systems without excessive downtimes. We also developed and characterized a fiber amplifier prototype at around 1550 nm that emits 100 W of linearly-polarized light in the TEM00 mode. This prototype uses an Er3+:Yb3+ codoped fiber that is pumped off-resonant at 940 nm. The off-resonant pumping scheme improves the Yb3+-to-Er3+ energy transfer and prevents excessive generation of Yb3+-ASE.