In this paper we describe a high power narrow-band amplified spontaneous emission (ASE) light source at 1030 nm center wavelength generated in an Yb-doped fiber-based experimental setup. By cutting a small region out of a broadband ASE spectrum using two fiber Bragg gratings a strongly constrained bandwidth of 12±2 pm (3.5±0.6 GHz) is formed. A two-stage high power fiber amplifier system is used to boost the output power up to 697 W with a measured beam quality of M2≤1.34. In an additional experiment we demonstrate a stimulated Brillouin scattering (SBS) suppression of at least 17 dB (theoretically predicted ~20 dB), which is only limited by the dynamic range of the measurement and not by the onset of SBS when using the described light source. The presented narrow-band ASE source could be of great interest for brightness scaling applications by beam combination, where SBS is known as a limiting factor.
We report on investigations of direct bonding of mono-crystalline Terbium Gallium Garnet (TGG) to sapphire for use as Faraday isolator in high power fiber laser applications. The technology of direct bonding allows joining of inorganic crystalline and non-crystalline materials without any auxiliary materials at high bonding strength. Lack of additional joining material and related absorption is very promising for high power laser applications. The ability to join different materials allows inserting sapphire as a heat spreader into the beam path for TGG cooling to avoid thermal lensing. All samples were subjected to extensive chemical cleaning and subsequent low temperature plasma activation before bonding. Bonding was performed under compressive forces in a high vacuum environment at moderate temperature. Optically transparent bonds with a very low fraction of defects were obtained. The size of the bonded area depends significantly on the samples' flatness
We report on the high power amplification of narrow linewidth laser radiation with close to diffraction limited beam quality using a large mode area photonic crystal fiber amplifier. The observation of threshold-like higher order mode amplification by transverse spatial-hole burning at the highest power level is reported. The measured M² stays below 1.3 but increases at the critical power level, where the fundamental mode turns into the next higher order mode. At the maximum power of 1.2 kW a linewidth of <80 pm limited by self-phase modulation is obtained
A high-power tunable Raman Amplifier is presented. The seed signal (varying from 1118 nm to 1130 nm in wavelength) was generated in a tunable Raman oscillator and fed into the Raman amplification stage. A conversion efficiency of up to 86 % was achieved and a maximum output power of over 200 W was measured. The Raman gain coefficient for the amplifier fiber was measured to be 0.76× 10-hoch14 m/W. Furthermore, the measured output power was compared with values obtained from simple mathematical model and a good agreement up to the highest output power of amplified signal was achieved
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