| 研究領域 | 光の螺旋性が拓くキラル物質科学の変革 |
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| 研究課題/領域番号 |
23H04571
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| 研究種目 |
学術変革領域研究(A)
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| 配分区分 | 補助金 |
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| 審査区分 |
学術変革領域研究区分(Ⅱ)
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| 研究機関 | 沖縄科学技術大学院大学 (2024)
北海道大学 (2023) |
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研究代表者 |
Pin Christophe 沖縄科学技術大学院大学, 量子技術のための光・物質相互作用ユニット, スタッフサイエンティスト (50793767)
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| 研究期間 (年度) |
2023-04-01 – 2025-03-31
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| 研究課題ステータス |
交付 (2024年度)
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| 配分額 *注記 |
3,770千円 (直接経費: 2,900千円、間接経費: 870千円)
2024年度: 1,430千円 (直接経費: 1,100千円、間接経費: 330千円)
2023年度: 2,340千円 (直接経費: 1,800千円、間接経費: 540千円)
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| キーワード | chiral optical force / angular momentum / vanadium dioxide / nonlinear trapping / topology |
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| 研究開始時の研究の概要 |
The orbital motion of optically trapped VO2 particles depends on by the spin and orbital angular momenta of the incident light. This work aims at elucidating the underlying spin-to-orbital momentum conversion mechanisms and demonstrate a new particle chirality-dependent optical sorting technique.
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| 研究実績の概要 |
In the first stage of the project, nonlinear optical trapping of VO2 particles has been demonstrated. Due to the laser absorption-induced heating and the consequent phase transition of the optically trapped VO2 particles, VO2 particles have been found to remain trapped in an orbit trajectory around the focused laser beam center. Laser power and polarization dependence have been experimentally studied.
Using VO2 particles purchased from a Japanese maker, direct transfer of angular momentum from the circularly polarized incident light to the orbiting trapped particle was demonstrated. Both the spin of the incident light and the orbital angular momentum of the trapped particle had the same direction (right-handed optical torque).
However, rotation direction reversal was also observed during the chemical growth of a trapped VO2 particle. When VO2 nanoparticles were dispersed in a precursor solution, trapped particle growth was demonstrated due to laser-induced hydrothermal synthesis reaction. During the particle growth process, the particle rotation was first rotating in the opposite direction ((left-handed optical torque) and then in the same direction as that of the incident light spin. Although this phenomenon can be explained by the interference between several Mie resonances of the dielectric-state-VO2 particle, it is still not clear why the metallic-state-VO2 particle has less effect.
A linear optical trap was created using a cylindrical lens and the first demonstration of spin-induced linear motion of trapped particles was achieved.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
Optical trapping of VO2 particles has been investigating using different polarization state of the incident laser beam. According to the initial plan, the rotation of trapped particles with different shapes was successfully controlled by manipulating the spin state of the incident light.
Focused Laguerre-Gaussian (optical vortex) beams have also been used to trap VO2 particles and study the influence of the orbital angular momentum of the incident light. More experiments are needed to evaluate the influence of the size of the trapped particle.
According to the initial plan, numerical simulation to explain the optical trapping and circular polarization-induced rotation mechanisms have been performed. It was found that for all particle sizes the optical torque acting on a VO2 particle located on a stable trapping orbit should be along the direction of spin of the incident light, in good agreement with the experiments.
In experiments where the chemical growth of trapped VO2 particles is performed, some data demonstrating an optical torque in the direction opposite to that of the incident light spin are still not well explained by the numerical model. Further refinement of the model and a better knowledge about the synthesized material properties are necessary to clarify that point.
After moving from Hokkaido University to Okinawa Institute of Science and Technology, I am building my new optical tweezers setup. The microscope and laser source were borrowed from the previous work place. Experiments using structured light beams will be performed as soon as the setup is ready.
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| 今後の研究の推進方策 |
During the second year, the project will be divided in three main research activities:
1. Further investigation of the spin and orbital angular momenta-controlled orbital rotation of VO2 particles optically trapped using a focused Laguerre-Gaussian beam. The particle size and shape dependence of the rotation control will be studied.
2. Numerical modeling of the interaction of a particle trapped in a light intensity gradient. The mechanism of right- and left-handed optical torques will be investigated.
3. Generation of optical fields with complex spin angular momentum spatial distribution. To demonstrate the particle size and chirality-dependent motion of the trapped VO2 particles, light fields with tailored spatial distributions of intensity and circular polarization will be prepared by holography technique.
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