Abstract
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.
Highlights
Pulsed laser deposition (PLD) is a quick, versatile method for depositing thin films comprising a wide selection of materials that include single elements, such as metals, or complex multi-component materials [1, 2]
With the uni-directional setup (Fig. 9a), there is a clear directionality to the surface structure and evidence of small surface particles shown in the inset, whereas bi-directional ablation (9b) while still producing some target structuring, has no obvious directionality nor evidence of surface particles
The peak-to-valley range shows a ~ 50% reduction in surface roughness for bi- as compared to uni-directional ablation. It is only a factor of 2 larger than the surface roughness present on a new and unused target. Both the reduction in directionality and scale of the surface structures is a significant improvement compared with uni-directional ablation
Summary
Pulsed laser deposition (PLD) is a quick, versatile method for depositing thin films comprising a wide selection of materials that include single elements, such as metals, or complex multi-component materials [1, 2]. PLD has been demonstrated as a viable technique for the growth of single-crystal planar waveguide devices fabricated from a range of materials, including doped sapphire (Al2O3) [3, 4], sesquioxides [5, 6] and in particular, garnets [7]. This can be a relatively fast deposition process, and to date, growth rates of 25-μm per hour have been achieved on. Other active garnet films, including Yb:GGG (gadolinium gallium garnet) and Yb:YGG (yttrium gallium garnet) have been used for efficient laser operation [10]
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