State-of-the-art high power Yb-doped large mode area fibers have been developed to a performance level able to reach the so-called mode instability threshold. In this contribution we will discuss the experimental results regarding the temporal evolution (build up and decay) of this effect to come closer to a comprehensive understanding of its driving mechanisms. Our investigations prove that the relevant time scale for build up and decay of mode instability is in the millisecond range and thus deliver experimental evidence of underlying thermal effects. To the best of our knowledge these are the first systematic, time resolved investigations on that topic.
We report on a high power fiber amplifier tandem pumped by an industrial style thin-disk laser. An output power of 1 kW and a very good slope efficiency of 73% have been obtained for a state-of-the-art photonic crystal fiber originally designed for short-pulse amplification. We also compare this result to an experiment, where a power of 2.9 kW could be obtained from a step-index large-mode-area fiber with the same slope efficiency.
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.
Fiber lasers have reached kW levels of output power. To achieve this level it is necessary to use reliable high-power components that sustain these power levels. Double-clad fibers (DCFs) are often used in high-power fiber lasers. Cladding-light strippers (CLSs) are used to remove unwanted light from the inner cladding of the DCF. This unwanted light consists of residual pump light or signal light that leaked into the cladding, thus requiring that the CLS removes both high-NA (>0.4) and low-NA (<0.1) light. Often high-index polymers are used to remove the unwanted light from DCFs1,2,3. Because the CLS has to be able to withstand several 100W and most polymers are not capable of exceeding temperatures more than 200°C, we investigated a CLS without polymers, based on an etching process. We present results from a CLS that was tested up to 500W of stripped power. We determined the angle dependency of the stripping efficiency by launching both high- and low-NA light into the fiber and evaluating the NA attenuation. Furthermore, we measured the dependency of the stripping efficiency on the length of the etched area and the etching time. With optimized parameters an attenuation of more than 20 dB when launching high-NA light and 6 dB with low-NA light was achieved. The CLS did not show any degradation in terms of attenuation or thermal behavior in a six-hour stability test
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