Atomic Beam Sources of Titanium in the Laser Coolable Metastable State

We present the development of two sources of atomic beams of titanium suitable for laser cooling applications: one based on laser ablation and one based on a titanium sublimation pump. Titanium, among several other transition metals, has been identified as a potential candidate for laser cooling. While titanium's ground state electronic spectrum is too complex for a reasonable laser cooling experiment, the a⁵F₅ metastable excited state possesses a near-cycling transition. However, another challenge is posed by the formidable material properties of titanium. With a melting point of 1668°C, standard atomic oven methods are not feasible. This has motivated us to develop methods to generate high flux beam sources of metastable titanium. One revolves around a titanium sublimation pump, which is a readily accessible, standard ultrahigh vacuum pump. The pump functions by running current through a tungsten filament embedded in a shell of titanium, heating the shell up to temperatures where sublimation is significant. The population of metastable atoms in a thermal beam is low, however we demonstrate significant enhancement by optically pumping the beam. The other source is based on laser ablation in a buffer gas, a well-tread path to atomic and molecular beams. Our apparatus is made simpler by the high capture velocity of metastable titanium, allowing for operation at room temperature. In addition, the high energies involved in ablation populate the metastable excited state without the need for optical pumping. The addition of titanium to the ultracold atomic physics toolbox could give access to advantageous optical clock transitions, simulations of novel quantum materials, and other applications enabled by the unique atomic structure. Further, our simplified atomic sources are applicable to other elements with low vapor pressures.