Femtceecond laserinduced nano-manipulation inside transparent materials

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We achieved the periodic nanostructuring inside various materials without surface damage by using interference field or polarizing properties of femtosecond laser pulse. These achievements were based on the interaction between the photon and plasmon induced by the laser irradiation, because the femtosecond laser pulses have together features of ultra high photon intensity and ultra fast pulse duration. Especially, laser energy can be injected into a material before the coupling between an electron and a phonon reaches a state of thermodynamic equilibrium. In the case of fused silica, a periodic nanostructure with a pitch of 200 nm and a width of 20 nm was self-organized perpendicular to the laser polarization direction by the femtosecond single laser beam irradiation. This periodic nanostructure (viz. nanograting) consisted of the density modulation of the oxygen defects, and then the glass composition in the oxygen defect regions are modified from SiO_2 to SiO_1.6. We also confirmed t … More hat the periodic voids were formed and aligned in the plane perpendicular to the polarization of the light field in the case of a TeO_2 crystal. We speculate that due to the weaker binding energy of Te-O and its lower melting point of 733 ℃, a void was formed inside TeO_2 crystal. On the other hand, in the case of multicomponent glass including alkaline metals and alkaline earth metals, the polarization-dependent nanograting structure can not be formed, while Na and Ca elements, which are modifier elements, diffused away from the focal point. In order to reveal the formation mechanism of nanograting structure we investigated how nanograting structure was affected according to the laser intensity. From the systematic experiments, we have confirmed that the pitch of nanograting was changed from 100 to 400 nm with increasing laser fluence. We interpreted that the nanograting formation was related to the plasma formation during laser irradiation, especially, the electron plasma temperature during laser pulse irradiation was the important factor for the nanograting formation. Based on these basic researches, we fabricated the integrated micro optical devices such as grating, polarizer, and optical attenuator inside glass. Less