| Project/Area Number |
15350121
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Inorganic industrial materials
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| Research Institution | Kyoto University |
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Principal Investigator |
HIRAO Kazuyuki Kyoto University, Graduate School of Engineering, 工学研究科, 教授 (90127126)
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| Co-Investigator(Kenkyū-buntansha) |
FUJITA Koji Kyoto University, Graduate School of Engineering, 工学研究科, 助手 (50314240)
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| Project Period (FY) |
2003 – 2004
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| Project Status |
Completed (Fiscal Year 2004)
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| Budget Amount *help |
¥13,300,000 (Direct Cost: ¥13,300,000)
Fiscal Year 2004: ¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 2003: ¥10,200,000 (Direct Cost: ¥10,200,000)
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| Keywords | Glasses / Femtosecond laser / Nanofabrication / Periodic structures / Three-dimensional integration / Plasmon / 周期構造形成 |
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| Research Abstract |
An intense femtosecond laser pulses have an electric field strength which approaches or even exceeds the strength of the electric field that holds valence electrons in transparent materials to their ionic cores. In this regime, the interaction between the laser pulse and the material become highly nonlinear. This nonlinear phenomena cause the change in the structure inside transparent materials. In this research, we carried out the basic research aiming at the internal modification of glasses and the development of three-dimensional optical circuit through nonlinear optical effect such as multiphoton process induced by femtosecond laser. In particular, we performed the experiments on nanofabrication inside glasses. The main results of this research are as follows. When SiO_2 glasses are irradiated with femtosecond laser with a repetition frequency of 200 kH (800 nm), we have observed self-organized periodic structures within the bulk. The structures consists of oxygen depleted regions
… More
of 20 nm size aligned in a direction perpendicular to the electric field of light wave and with periods as small as 140 nm. These are the smallest embedded structures ever created by light. The mechanism of this self-organized nanostructure is interpreted in terms of interference between the incident light field and the electric field of bulk electron plasma wave, and then resulting in the periodic modulation of electron plasma concentration and the structural changes in glass. In the case of TeO_2 single crystal, periodic nanovoids are formed by an explosive expansion of the ionized material in the focal volume into the surrounded by densified matrix, i.e., microexposion. In the microexposion, the increase in the pressure is caused by a rise in temperature at constant volume. We speculate the periodic nao-void formation mechanism as follows. In the early stages of the interaction between light field and electron plasma wave, periodic pattern of electron density arises in common with SiO_2 glass. Due to the weaker binding energy of Te-O and lower melting point of 730 $degree$, a void formed in the maximum of the electron plasma density distribution. We have directly written submicron photonic structures into the internal bulk of silica glass and TeO_2 single crystal with a femtosecond laser system. The nanostructures are observed to strongly reflect in the blue spectral region but only along the polarization axis of the original writing beam. We think that the observed phenomenon can arise from a self-organized periodic refractive index modulation. The effect can explain systematically the origin of other observed anisotropic behavior reported with such pulsed laser patterning. These polarization-dependent nanostructures should be useful in many monolithic photonic devices and can be harnessed for information storage, micro-electromechanical systems(MEMS) applications or quasi-phase matching where nanoscale periodic structuring is required. A detailed mechanism of the structural changes responsible for the nanograting formation is under investigation. Less
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