The laser system is placed on two optical tables with dimensions 2.5 m x 1.5 m, and it comprises twelve tunable diode lasers (DL Pro TOPTICA Photonics) with external-cavity resonator in Littrow configuration, three fixed-frequency diode lasers, a frequency doubler, an optical frequency comb and a continuous-wave Titanium:Sapphire laser (CW Ti:Sa laser). The diode lasers are classified in terms of their center wavelength as follows:

• 4 UV lasers at 397 nm needed for laser cooling of 40Ca+ by driving the S1/2 - P1/2 electric-dipole transition.
• 4 IR lasers at 866 nm required to restore the cooling cycle when it is interrupted via the decay from P1/2 to the dark state D3/2, which can occur with a probability of 7%.
• 2 IR lasers at 854 nm to drive the D5/2 - P3/2 transition, since the probability of populating the D5/2 dark state from the P1/2 state scales with the magnetic field strength. The branching ratio relative to the main decay is proportional to the square of B, as measured by the group of Prof. Richard Thompson at Imperial College London (link to the manuscript). In this scenario, we need 4 additional 854 nm beams to address all D5/2 - P3/2 pumping transitions that arise in the 7-T magnetic field regime. The additional 854 nm beams are generated by feeding an electro-optical modulator (EOSPACE) with the two existing 854 nm laser beams. A microwave signal generator with frequency range from 9 kHz to 40 GHz along with an amplifier is used to electrically feed the EOM.
• Two tunable diode laser at 423 nm (DL Pro TOPTICA Photonics) and three free-running diode lasers at 375 nm (iBeam TOPTICA Photonics), needed for accomplishing the photoionization of the neutral Ca atoms injected to the ion traps.
• A CW Ti:Sa laser (Sirah Matisse TX) that provides very wide tunability (700 to 1000 nm) and high output power (>0.5 W). The Ti:Sa laser served as laser source in different frequency regimes. It is also coupled to the frequency doubler (SHG Pro TOPTICA Photonics).
  

The wavelength of the lasers is measured and stabilized using a Fizeau-based wavelength meter (HighFinesse WSU-10) with an absolute accuracy of 10 MHz (3 sigma). A stabilized HeNe laser (632.9909463 nm) with high frequency stability provides the reference value to calibrate the wavemeter. The setup to couple all 12 laser beams needed for the Penning trap experiment has been completed in January 2016, and further preparations of the imaging system have been made to study the fluorescence of 40Ca+ ions stored in Penning traps at 7 T.

In December 2015, an optical frequency comb (Menlo Systems FC1500-250-WG) was installed in the laboratory. This device provides absolute frequency measurements with very high precision, and therefore provides an accurate frequency stabilization of laser sources. At present time, the whole apparatus is operative and ready to start with the tests of the Ti:Sa laser locking to the frequency comb in order to improve the frequency stabilization.

The Penning traps beamline comprises a laser-desorption ion source, a transfer section, a Penning traps system and a time-of-flight (TOF) section for identification. The laser desorption ion source for injecting ions in the traps is in operation since 2013. First trapping was already accomplished in 2014 and, by the end of 2014, it was possible to obtain the so-called cooling resonance for 40Ca+ ions and other ion species. The Penning trap system consists of two traps: a preparation trap and a measurement trap. The preparation trap is made of stack of cylinders for cooling and separation of the incoming ions and the measurement trap exhibits a novel geometry to study the laser cooling of 40Ca+ ions in the 7 T magnetic field.

In 2018, a linear RF trap was devised and installed in the lab. The trap design is based on the one developed by the University of Innsbruck and is comprised of four blade-shape (RF) electrodes and two tip-shape (DC) electrodes that provide the confinement of the ions in all three directions. We intend to trap single calcium ions and dramatically reduce their energy via laser cooling. The detection of the ions is realized by means of collection of the emitted photons due to interaction of the ions with the laser light. The fluorescence photons are collected by an in-vacuum lens (see picture above) and then imaged onto an EMCCD camera.

The design of the trap and the experimental setup along with the detection of the first fluorescence images of calcium ions in the trap are part of two Master Thesis that have been defended in 2018 and 2019, respectively.