High Power Ultraviolet Lasers for Beam Cooling at SIS100

Laser cooling of ion beams has been shown to be a powerful technique in storage rings in order to generate high brilliance beams. Using a narrow linewidth cw laser it is possible to generate a cool relativistic C3+ beam in the ESR with a relative momentum spread of 〖10〗^(-7) [1]. Even though the achievable temperature is exceedingly low when the range of cooling force is rather narrow, intrabeam scattering allows ions to leave the capture range. The simultaneous use of cw cooling and white light cooling with spectral broadened pulsed laser light could help to overcome this effect [2]. Due to the necessary atomic transition, the number of lithium-like ions accessible at the ESR is considerably small. At the SIS100, however, laser cooling will be feasible for a large number of lithium-like ions but the demand for laser power increases rapidly with the atomic number Z [3]. To fulfill the requirements two laser systems have been developed. The pulsed laser system emitting at 257 nm has a maximum repetition rate of 10 MHz and adjustable pulse durations in the range between 100 and 700 ps. To generate high power cw laser light at 257 nm a novel enhancement cavity for second harmonic generation (SHG) was built up. In this setup it is possible to obtain 600 mW output power over hours without any sign of degradation of the crystal. This is possible with the very same off-the-shelf BBO crystal which cannot provide a stable power of several mW in a conventional SHG resonator [4]. In this talk the requirements for laser cooling of lithium-like ions at SIS100 will be discussed and the two ultraviolet high power laser systems will be presented. U. Schramm et al 2005 Hyperfine Interact 162 181-188 S. N. Atutov et al 1998 Physical review letters 80 2129 L. Eidam et al 2018 Nucl. Instrum. Methods Phys. Res. A 887 102–13 D. Kiefer et al 2019 Laser Phys. Lett. 16 075403