Particulate reduction in PLD-grown crystalline films via bi-directional target irradiation

We present a novel variation of the pulsed laser deposition (PLD) technique, aimed at reducing the number of particulates produced and consequently the linear propagation loss observed in the resulting crystal waveguides. The approach relies upon configuring the system to effectively provide bi-directional ablation, whereby the incidence angle of the fixed pulsed laser beam with respect to the target surface changes sign, depending upon the rotation angle and position of the target. Such an alternating ablation direction is intended to reduce the buildup of undesirable periodic surface structures, such as directional cones, believed to be a major source of particulates within the growing film while keeping the plume stationary with respect to the substrate. We show that targets ablated using this technique have fewer directional structures and a decreased surface roughness. Furthermore, using PLD-grown Y3Ga5O12 as the exemplar crystal film, we compare growths with uni- and bi-directional ablation and demonstrate reduction from ~ 0.9 to ~ 0.23 dB/cm in the average waveguide propagation losses via the latter.