Fig. 6: Schematic of the optical system used for producing and laser cooling Be+.

A TOPTICA TA-FHG PRO produces 313 nm light using two frequency doubling stages with a 1252 nm amplified diode laser. A half-wave plate (λ/2) and a polarising beam splitter (PBS) split the 313 nm beam into the off-axis path (purple) and the on-axis path (cyan). Each beam path is actively stabilised with a feedback system utilising position-sensitive detectors (PSD) and piezo-actuated mirrors. Quarter-wave plates (λ/4) placed before the beams enter the vacuum chamber control polarisation. Be⁺ ions are produced by focusing pulsed 355 nm light from a Quantel Ultra20 laser onto a beryllium target (beam path in orange). The pulse energy is controlled with a half-wave plate and a PBS. A 50:50 beam splitter (BS) is used to direct half of the pulse to a pyroelectric sensor to monitor pulse energy. The rectangles with diagonal lines in the vacuum chamber represent linear translators, which are used to change the instruments that are aligned with the axis of the trap electrodes.