High Power Fibre Laser System for a High Repetition Rate Laserwire

We present the development of a high power fibre laser system to investigate its suitability for use in a transverse electron beam profile monitor i.e. a laserwire. A system capable of producing individual pulses up to $165.8 \pm 0.4 \mu$J at 1036 nm with a full-width at half-maximum of $1.92 \pm 0.12$ps at 6.49 MHz is demonstrated using a master oscillator power amplifier design with a final amplification stage in a rod-type photonic crystal fibre. The pulses are produced in trains of 1 ms in a novel burst mode amplification scheme to match the bunch pattern of the charged particles in an accelerator. This method allows pulse energies up to an order of magnitude greater than the steady-state value of $17.0 \pm 0.6 \mu$J to be achieved at the beginning of the burst with a demonstrated peak power of $25.8 \pm 1.7$ MW after compression. The system is also shown to demonstrate excellent spatial quality with an $M^{2} = 1.26 \pm 0.01$ in both dimensions which would allow nearly diffraction limited focussing to be achieved.