A fiber laser is disclosed comprising a single mode or low-order-mode cladding pumped fiber laser oscillator or preamplifier, a cladding pumped fiber laser power amplifier to guide multiple transverse modes, wherein an output from the oscillator or preamplifier is applied through a mode mixing means to the power amplifier to provide that a laser signal of the cladding pumped fiber laser power amplifier is emitted from the fiber laser power amplifier in the multiple transverse modes.