Fiber lasers and amplifiers are capable of producing kilowatts of optical output power with diffraction-limited beam quality. We present compact and robust high-power beam combiners that can be used for coherent and spectral beam combining for the scaling of fiber laser systems to high brightness and extremely high optical power. This beam combiner approach is based on a fully monolithic, all-glass solution that can withstand harsh environmental conditions and extremely high optical powers. The installation space and weight for this beam combiner is very small, even for ⪆100 combined laser beams.
Fiber lasers and amplifiers are capable of producing kilowatts of optical output power with diffraction-limited beam quality. We present high precision high power fiber arrays which can be used for coherent and spectral beam combining for scaling of fiber laser systems to high brightness and high power. The availability of CO2 laser-based fiber splicing systems that can control the position and size of the heating zone has opened up new possibilities in the splicing of multiple fibers (fiber arrays) to large optical elements. In our experiments we realized linear fiber arrays with PM and non-PM large mode area (LMA) fiber with no gap between the individual fiber channels (DC-PM-20/400 and DC-PM-25/250). The fibers were spliced to a large AR-coated fiber end cap. The misalignment of the PM axes of all fiber channels was less than ±1 degree and the inline tolerance of the fiber array was below ±2.5µm. Each fiber channel was tested up to an optical output power of 1kW.
Single-frequency Yb3+ and Er3+:Yb3+ fiber amplifiers (YDFA/EYDFA) in MOPA configuration operating at 1064 nm and around 1550 nm are promising candidates to fulfill the challenging requirements on laser sources for the next generation of interferometric gravitational wave detectors (GWDs). They offer high beam quality, long-term stability and allow for excellent thermal management. We developed an engineering fiber amplifier prototype at 1064 nm emitting around 200W 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 maintenance procedures and repair. In addition, commercial available fibers increase the flexibility of the entire system. We also developed and characterized a fiber amplifier prototype at 1556 nm that emits 100W of linearly-polarized light in the TEM00 mode. The EYDFA is pumped off-resonantly at 940 nm to enhance the Yb3+-to-Er3+ energy transfer efficiency and enable a higher amplified spontaneous emission (ASE) threshold. In addition to that, we performed measurements to study phase to intensity noise coupling via the Kramers-Kronig relation above the stimulated Brillouin scattering (SBS) threshold, as it was proposed based on numerical simulations. This effect is based on an asymmetric gain spectrum, which we measured experimentally and used for the reconstruction of the broadband excess intensity noise.
We report on novel fabrication schemes of versatile cladding light strippers and end-caps via CO2 laser radiation. We integrated cladding light strippers in SMA-like connectors for reliable and stable fiber-coupling of high-power laser diodes. Moreover, the application of cladding light strippers in typical fiber geometries for high-power fiber lasers was evaluated. In addition, we also developed processes to fuse end-caps to fiber end faces via CO2 laser radiation and inscribe the fibers with cladding light strippers near the end-cap. Corresponding results indicate the great potential of such devices as a monolithic and low-cost alternative to SMA connectors.
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.
Spectral beam combining of Tm-doped fiber lasers can increase the laser output power while simultaneously maintaining the single mode beam quality. We report on a spectral beam combining technique based on highly efficient in-housemade WDM cascade. We demonstrate continuous wave power combining employing a WDM cascade consisting of four fiber laser sources with emission wavelengths of 1920, 1949, 1996 and 2030 nm. A combined power of up to 38 W resulted in a combining efficiency of 69%.
Amplification of a gain-switched laser diode is demonstrated in an all-fiber based setup. The amplified spontaneous
emission between two consecutive pulses was investigated quantitatively in the time domain. A maximum pulse energy
of 13 μJ at a repetition rate of 1 MHz and a pulse duration of 40 ps was extracted, corresponding to a peak power of 270
KW. Temporal pulse deformation due to intrapulse Raman scattering was observed.
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