A pulsed, high-repetition laser source for laser cooling at storage rings

We present an all diode-pumped picosecond solid-state Master-oscillator power-amplifier (MOPA) for extending laser ion-cooling to broad momentum spread applications. The challenge of the system lies in the generation of bandwidth-limited pulses with a pulse duration of 70ps and energies at the 100µJ level. The pulses with a duration of 170fs were generated in a commercial Yb:KGW mode-locked oscillator with a repetition-rate of 50MHz. Inside a subsequent regenerative amplifier with an intra-cavity dielectric grating the pulse bandwidth is reduced by 5 orders of magnitude which corresponds to 20pm at a center-wavelength of 1028nm. The system allows a tuning range between 1028 and 1032nm. Finally, the output is frequency quadrupled (forth harmonic generation) to 257nm, which is in the range of the cw laser lines used for laser-cooling. Due to thermal and damage issues the average power was limited to 50mW in the infra-red at a maximum repetition rate of 500Hz.