A photon detection system has been developed for collinear laser spectroscopy measurements at the Beam COoling and COllinear LAser spectroscopy (BECOLA) facility at NSCL. The system is based on a design from the University of Mainz, and relies on an ellipsoidal reflector to transport fluorescent light to a photomultiplier tube. “Blue” and “red” photon detection systems were designed to cover the desired wavelength ranges. Simulations of the detection system were performed using FRED optical engineering software, and commissioning measurements were carried out with a 15 keV Ca+ beam to evaluate performance and to optimize the “blue” photon detection system for the BECOLA facility. Signal to noise measurements with different arrangements of beamline apertures showed that apertures are necessary both upstream and downstream of the reflector to reduce scattered laser light. Signal to noise ratio measurements for various iris sizes at the second focal plane of the reflector showed that the signal to noise ratio increased with iris area less than 12.7 mm in diameter, and then saturated with increasing size. The signal distribution was found to peak at the second focal point of the ellipsoidal reflector, which was well reproduced by the simulations. The background distribution was uniformly distributed over the area of the second focal plane that was measured. Overall sensitivity of 1 photon per 128 ions was achieved with the present “blue” photon detection system.
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