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Generation of high-energy single pulses and pulse clusters in ytterbium fibre lasers with quasi-synchronous modulation of the pump power

Additional capabilities of the method of quasi-synchronous pump power modulation developed by the authors for nanosecond high-energy pulsed oscillation of fibre lasers with a long-lived (about 1 ms) upper laser level are investigated. Using an Yb fibre laser as an example, it is shown that quasi-synchronous pump power modulation makes it possible to generate not only a periodic sequence of single nanosecond pulses, but also regular pulse clusters with a controlled number of nanosecond subpulses that make up a cluster. In addition, the feasibility of scaling the energy of laser pulses obtained by the method of quasi-synchronous modulation of the pump power is studied when proceeding to the use of active double-clad fibres and higher-power multimode pump sources. Pulses with energies up to 430 nJ are obtained in a laser configuration maintaining linear polarisation of radiation. The results obtained significantly expand the possibilities of applying the method of quasi-synchronous modulation of the pump power in conventional fibre lasers based on stimulated emission.