A Laser Amplifier

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An optical fibre laser or amplifier device is disclosed, comprising : a rare-earth-doped multi-clad optical fibre having at least three cladding layers 801, 810, 811 , one or more multimode pump laser diodes 301, and a means of multiplexing a laser signal and the pumping radiation, adapted so that a fraction of the stray signal light originating within the device is captured by one of the intermediate cladding layers of the rare-earth-doped fibre and guided out of the laser structure through the multiplexing system resulting in a reduction in the amount of stray signal radiation 813 impinging upon the pump laser diodes. Alternatively the device (Figure 3) may have a rare-earth-doped multi-clad optical fibre having at least two cladding layers 310, 311, and one or more passive multi-clad optical fibres having at least three cladding layers , one or more multimode pump laser diodes 301, and a means of multiplexing a laser signal and the pumping radiation, adapted so that a fraction of the stray signal light originating within the device is captured by one of the intermediate cladding layers of the passive multi-clad fibre and guided out of the laser structure through the multiplexing system resulting in a reduction in the amount of stray signal radiation impinging upon the pump laser diodes. Other variations and embodiments are disclosed.