Reduction of power fluctuation of laser light for collinear laser spectroscopy experiments at BECOLA facility at NSCL*

The BEam COoler and LAser spectroscopy (BECOLA) facility at NSCL/MSU is designed to determine fundamental properties of the atomic nucleus such as the charge radii, nuclear spins and electromagnetic moments. Commissioning tests of BECOLA have been completed using a stable $^{39}$K beam produced from an offline ion source. The $^{39}$K beam was then cooled and bunched using a radiofrequency cooler and buncher, propagated collinearly with laser light and resulting fluorescence was detected. The laser light that was co-propagated with the beam was transported to the experimental area from a remote laser room via a single-mode optical fiber. Random rotation of the polarization of the laser light led to a large fluctuation in laser power, and hence a poor signal-to-noise ratio for the fluorescence measurement. A laser power controller was introduced to mitigate the power fluctuations. The performance characteristics of the power-stabilization system as well as the collinear laser spectroscopy of the bunched $^{39}$K beam will be discussed.