Abstract
AbstractWe present a theoretical study of mode evolution in high-power distributed side-coupled cladding-pumped (DSCCP) fiber amplifiers. A semi-analytical model taking the side-pumping schemes, transverse mode competition, and stimulated thermal Rayleigh scattering into consideration has been built, which can model the static and dynamic mode evolution in high-power DSCCP fiber amplifiers. The mode evolution behavior has been investigated with variation of the fiber amplifier parameters, such as the pump power distribution, the length of the DSCCP fiber, the averaged coupling coefficient, the number of the pump cores and the arrangement of the pump cores. Interestingly, it revealed that static mode evolution induced by transverse mode competition is different from the dynamic evolution induced by stimulated thermal Rayleigh scattering. This shows that the high-order mode experiences a slightly higher gain in DSCCP fiber amplifiers, but the mode instability thresholds for DSCCP fiber amplifiers are higher than those for their end-coupled counterparts. By increasing the pump core number and reducing the averaged coupling coefficient, the mode instability threshold can be increased, which indicates that DSCCP fibers can provide additional mitigation strategies of dynamic mode instability.
Highlights
Fiber laser systems with near diffraction limited beam quality are an important laser sources, which can be used in various areas, such as achieving high power laser by beam combination [1], acquiring high power visible light by frequency doubling [2], or realizing high precision industry materials processing [3]
Due to the accumulated heat load at high average power, severe dynamic mode coupling - mode instability has been triggered in the fiber lasers [8, 9], which is the physical manifest of stimulated thermal Rayleigh scattering in fiber, and currently limits the power scaling and application area expanding of fiber laser systems [10,11,12]
It’s a big challenge to change certain parameters while keeping the rest ones unchanged. This can be realized in theoretical study, which means that critical insights into the mode instability of distributed side-coupled cladding-pumped (DSCCP) fiber lasers require the help of theoretical work
Summary
Fiber laser systems with near diffraction limited beam quality are an important laser sources, which can be used in various areas, such as achieving high power laser by beam combination [1], acquiring high power visible light by frequency doubling [2], or realizing high precision industry materials processing [3]. It’s a big challenge to change certain parameters while keeping the rest ones unchanged This can be realized in theoretical study, which means that critical insights into the mode instability of DSCCP fiber lasers require the help of theoretical work. It is known that the mode instability thresholds dependent on the pump power distribution [30, 31], and the mode instability thresholds for DSCCP fiber lasers must be different from those of ECCP fiber laser systems, which need to be studied as the output power of DSCCP fiber amplifiers scales up to multi-kilowatt level [32,33,34]. Semi-analytical model has been built by developing transversallyresolved steady state rate equations for DSCCP fiber, which has taken the side pumping schemes, transverse mode competition and stimulated thermal Rayleigh scattering into consideration. The results are discussed with the latest understanding of mode instability
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