Ultrafast defect manipulation with optical anisotropy in fused silica
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1230-MM07-05
Ultrafast defect manipulation with optical anisotropy in fused silica Yasuhiko Shimotsuma1*, Masaaki Sakakura1, Peter G. Kazansky2, Kiyotaka Miura3, Kazuyuki Hirao3 1 Innovative Collaboration Center, Kyoto University, Kyoto, Kyotodaigaku-Katsura, 615-8510, Japan 2 Optoelectronics Research Centre, University of Southampton, University of Southampton, SO17 1BJ, United Kingdom 3 Department of Material Chemistry, Kyoto University, Kyoto, Kyotodaigaku-Katsura, 615-8510, Japan ABSTRACT We report the evidence that the oxygen defects induced by focusing an intense infrared femtosecond laser pulse in fused silica can be self-organized by the interference pattern between photon and electron plasma wave. Self-organized nanostructure with a sub-wavelength modulation in refractive index exhibits form birefringence which is rewritable and directionallycontrollable. Intriguingly, such optical anisotropy, which indicates a remarkable non-reciprocity, has initially evolved from residual birefringence originated from internal stress distribution due to local heating followed by structural change, regardless of interpulse time. This anisotropic light-matter interaction could be interpreted in terms of an asymmetric relation between light polarization and pulse front tilt. Apart from fundamental understanding of self-organization mechanism, the direction of encoded birefringence can introduce an entirely new concept for rewritable optical storage beyond the diffraction limit of light. INTRODUCTION Following the recent progress on femtosecond laser technologies, electron localization during the femtosecond time scale [1] and alignment of molecules in gas phase [2] is widely studied. Besides, material processing with ultrafast lasers has recently attracted considerable interest [3] due to a wide range of applications including laser surgery [4], 3D micro- [5, 6] and nano-structuring [7, 8]. Due to short pulse duration, a key advantage of using femtosecond laser pulses for material processing is that, the energy can be deposited rapidly and precisely in the material. Meanwhile, oxygen vacancies affect fundamental properties of material ranging from ionic and electronic conductivities [9], light emitting [10], to form birefringence [7]. However, such oxygen defect can be localized by intrinsic charge compensation or external electric field, the dynamics of this self-organization in glass under an intense light field has remained poorly understood. By using a femtosecond double pulse configuration, we experimentally demonstrated that the self-organization of the oxygen defect in fused silica is rewritable and directionally controllable within a time scale of 70 ± 40 fs, which corresponds to the pulse width inside bulk fused silica, despite the fact that the structural changes occur on a longer timescale. In a single beam experiment, we have observed that the self-organization was developed initially from residual birefringence originated from internal stress due to thermal distribution with steep gradients. Finally, form biref
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