Control over the crystalline state of sapphire

Control over the crystallanity and chemical reactivity of sapphire (Al ₂O₃) using femtosecond pulse exposure was investigated. Crystalline-to-amorphous and amorphous-to-polycrystalline transitions were induced inside a sapphire sample using single and multi-pulse radiation. The method allowed the fabrication of a 3D network of channels without apparent constraints on their length. Multipulse exposure of sapphire caused partial recrystallization of the amorphous phase. The results showed high selectivity of wet etching in sapphire optically amorphized by the pulses. It was also observed that the crystallinity of sapphire can be controlled with a precision of several nanometers by the appropriate choice of exposure conditions. It was demonstrated that matter can be subjected to extreme pressure by commonly available femtosecond laser radiation.