schematically illustrates the employed set-up. A BaTiAl6O12-coated and an uncoated sapphire wafer were cut into 1010 mm2. The uncoated substrate was then placed over the BaTiAl6O12 (BTAO) coated substrate leaving the BaTiAl6O12 thin film in between acting as an absorber first and glass solder laser later .The set-up for the laser bonding is the same shown previously in, in which a custom-made sample holder was used in order to bring both sapphire substrates in close proximity. The irradiation source was a pulsed 5 ns 532 nm nanosecond Nd: YAGlaser (Xiton Photonics laser implemented into a microSTRUCT C laser micromachining work station by 3D-Micromac AG), operatedat 50 kHz.An objective of 255 mm of focal length was employed and the beam diameter is 20 mm. The laser beam was focused precisely at the interface between the upper substrate and the fresnoite thin film. A galvanometer scanner unit was employed, and the laser beam moves over the workpiece, tha tremains fixed.
A pattern consisting of 50 horizontal lines separated by 100 mm forming a square of 55 mm2 was developed. The irradiated lines follow a wobble trajectory, which corresponds to a circular motion of the laser beam.