Abstract

The laser-induced periodic bulk nanograting structure inside of the material is one of the intriguing structure induced by the femtosecond laser pulses. Even now the formation mechanism of bulk nanogratings is also still a mystery [1,2]. In the case of relatively simple composition glass (SiO₂, GeO₂, etc.), the subwavelength stripe-like regions of lower oxygen concentration including nanovoids exhibit lower density, the optical anisotropy in form birefringence can be successfully induced [3,4]. We have recently observed that the bulk nanogratings were also formed in Al₂O₃-Dy₂O₃ binary glass with a low glass formation ability [5]. In this case, we confirmed that the partially crystallized structures were periodically induced at the nanoscale. Particularly, we have confirmed that the garnet (Dy₃Al₅O₁₂) and the perovskite phase (DyAlO₃) can be selectively precipitated according to the laser energy. To make an Al₂O₃-Dy₂O₃ glass with a low glass formation ability, we employed an aerodynamic levitation with laser melting method. The femtosecond laser pulses (pulse duration: 50 fs, wavelength: 800 nm, repetition rate: 250 kHz) were focused at 100 µm below the Al₂O₃-Dy₂O₃ glass sample surface. After laser irradiation, local structures of the modified region were investigated by means of transmission electron microscopy.

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