Three-Dimensional Residue-Free Volume Removal inside Sapphire by High-Temperature Etching after<?layout cmd="newline"?> Irradiation of Femtosecond Laser Pulses

We applied the femtosecond laser-assisted etching technique, that is, irradiation of focused femtosecond laser pulses followed by selective chemical etching, to volume removal inside sapphire. At room temperature, volume etching only slightly advanced while residue remained inside the volume. By increasing the etching temperature, complete volume etching without residue was achieved. Complete etching was, however, accompanied by undesirable phenomena of surface pits or cracks, which are expected to be excluded through further improvement of processing.