Fiber lasers have been established as a reliable power-scalable laser architecture in the last years. Continuous-wave output powers well above the kW-barrier have been demonstrated with diffraction-limited beam quality. However, even a state-of-the-art fiber laser is eventually limited by nonlinear effects, fiber facet damage or thermal issues. Spectral combining of continuous-wave fiber lasers is a well known and very promising power scaling technique to obtain power levels far beyond the limitations of a single fiber emission without significant beam quality degradation. Spectral beam combination setups provide an overlap of the individual beams in the near and far fields without the need for complex phase control. With the technique of spectral beam combination several beams with different wavelengths are superposed. Each beam has a different incident angle on a grating in such a way that the diffraction angles for all beams are identical. Thus, spectral beam combination trades brightness enhancement with loss of spectral purity.

    Spectral Beam Combining of CW Fiber Lasers

    Spectral beam combining of Yb-doped fiber lasers with high efficiency
    S. Klingebiel, F. Röser, B. Ortaç, J. Limpert and A. Tünnermann
    J. Opt. Soc. Am. B, vol. 24, pp. 1716-1720 (2007)

    We present a combination of three master-oscillator power-amplifier fiber laser systems to a total power of 153 W. Due to the employment of single-polarization low-nonlinearity photonic crystal fibers in the main amplification stages a combining efficiency as high as 95% has been realized. The measured beam quality of M2=1.2 for each laser does not decrease for the combined beam. Thus this setup provides excellent opportunities for brightness enhancement.

    Spectral Beam Combining of Pulsed Fiber Lasers

    200 W average power, 1 mJ pulse energy from spectrally combined pulsed sub-5 ns fiber laser source
    O. Schmidt, B. Ortaç, J. Limpert, A. Tünnermann and T. Andersen
    Photonics West, San Jose, California, USA, 24-29 January 2009. Proc. SPIE – The-International Society for Optical-Engineering, vol. 7195, 719519 (Feb. 19, 2009)

    Spectral combining of four high power pulsed fiber lasers is demonstrated. More than 200W of average output power at 200 kHz repetition rate resulting in 1mJ of pulse energy could be achieved in a spatially and temporally overlapped beam. A 1740 lines/mm dielectric reflection grating was used to combine the beams with an efficiency of ~93% and a beam quality of M2=1.3 (vertical) and 1.8 (horizontal), respectively. To our knowledge this represents the highest average output power ever achieved in a spectrally combined pulsed fiber amplifier setup