Browsing by Author "Omatsu, Takashige"

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Direct generation of red and orange optical vortex beams from an off-axis diode-pumped Pr3+:YLF laser
(2019-06-24)
Ma, Yuanyuan
;
Valles, Adam
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Tung, Jung-Chen
;
Chen, Yung-Fu
;
Miyamoto, Katsuhiko
We demonstrate the direct generation of visible vortex beams at 640 nm and 607 nm by employing an off-axis pumping scheme in a diode end-pumped Pr3+:YLF laser. A detailed numerical analysis, based on the coherent superposition of Hermite-Gaussian modes with different amplitudes and phases, is perfectly consistent with the experimentally observed lasing modes. The maximum vortex output powers have been measured to be 808 mW and 211 mW at a pump power of 3.16 W, for the wavelengths of 640 nm and 607 nm, respectively. We also demonstrate the handedness control of the generated vortex beam. Such a visible vortex laser can potentially be applied in super-resolution fluorescent microscopes and micro-fabrication research. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Direct generation of vortex beams from a diode-pumped Pr3+:YLF laser
(2019-01-01)
Ma, Yuanyuan
;
Tung, Jung-Chen
;
Miyamoto, Katsuhiko
;
Omatsu, Takashige
;
交大名義發表
We have demonstrated the direct generation of visible structured light beams, scalar and vector vortex modes with a wavelength of 640nm from a diode-pumped Pr3+:YLF laser by employing an off-axis pumping technique. A maximum output of similar to 100 mW was achieved at a pump power of 1.2 W. Such red structured light beams will be potentially applied to super-resolution fluorescent microscopes and microfabrications. (C) 2019 The Author(s)
"Freezing" of NaClO3 Metastable Crystalline State by Optical Trapping in Unsaturated Microdroplet
(2018-02-01)
Niinomi, Hiromasa
;
Sugiyama, Teruki
;
Miyamoto, Katsuhiko
;
Omatsu, Takashige
;
應用化學系
We reversibly controlled phase conversion between a microdroplet of a NaClO3 unsaturated aqueous solution and a metastable single crystal, which is usually a short-lived phase in spontaneous crystallization, simply by irradiating a tightly focused visible continuous-wave (CW) laser to the microdroplet. The laser irradiation allowed the metastable crystal to generate and stably grow without a polymorphic transformation. This successful metastable phase control is attributed to the combination of the advantage of optical trapping-induced nucleation that nucleation takes place from unsaturated mother solution and the advantage of microdroplet method, which suppresses additional nucleation leading to the transformation. In situ observation shows the crystal dissolves when the laser irradiation is stopped, whereas the laser irradiation stabilizes the crystal even if the size of the crystal becomes larger than that of focal spot. These observations indicate that a change in the relative magnitudes of chemical potentials between solution/crystalline phases. This change is possibly promoted via crystal growth by trapping of crystalline clusters in optical potential well formed on a crystal surfaces originating from "light propagation" through the crystal. Our results shed a light not only on polymorph control but also on a method to prepare a longer-lived achiral precursor for analysis on achiral chiral transition by "freezing" a kinetic pathway of chiral crystallization.
In Situ Microscopic Observation on Surface Kinetics in Optical Trapping-Induced Crystal Growth: Step Formation, Wetting Transition, and Nonclassical Growth
(2019-07-01)
Niinomi, Hiromasa
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Sugiyama, Teruki
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Ujihara, Toru
;
Guo, Suxia
;
Nozawa, Jun
Optical trapping-induced crystallization (OTIC) has provided significant impacts on the control of crystallization. Although consecutive research studies have implied that the optical potential formed on the crystalline surface by light propagation contributes to the crystal growth by observing bulk crystal growth, direct observation from the viewpoint of the surface kinetics represented as Burton, Cabrera, and Frank theory is still lacking. Here, we directly show the surface state modification by microscopically observing step formation/dissolution and wetting transition of a solution thin layer over a sodium chlorate crystalline surface upon turning on/off the laser irradiation. Irradiating/stopping of the laser irradiation to the crystal led to the formation/dissociation of several tens of micron-sized islands constructed by bunched steps. It was also found that the wetting transition of the solution thin film over the entire crystal surface took place simultaneously with the laser irradiation, evidencing that the interfacial potential was modified from repulsive to attractive potential by light propagation. Moreover, the observation visualized nonclassical crystal growth like the cluster assimilation scenario. Our observation not only leads to a deeper understanding of the mechanism of OTIC but also can provide the opportunity to reach unusual crystal growth phenomena beyond the classical limit and has implications for crystal growth modified by an external field.
In Situ Observation of Chiral Symmetry Breaking in NaClO3 Chiral Crystallization Realized by Thermoplasmonic Micro-Stirring
(2018-08-01)
Niinomi, Hiromasa
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Sugiyama, Teruki
;
Tagawa, Miho
;
Harada, Shunta
;
Ujihara, Tom
We have found that large chiral symmetry breaking in chiral crystallization can be achieved by irradiating a several milliwatts focused laser to a plasmonic nanolattice immersed in a stagnant NaClO3 saturated aqueous solution. Several hundreds of chiral crystals with the same handedness showed up in the solution after the laser irradiation in contrast to spontaneous crystallization. In situ microscopic observation for the early stage of the crystallization in the vicinity of the focal spot revealed that microbubble generation followed by large supersaturation increase, in which supersaturation reaches 360%, promotes several numbers of crystal nucleation in the vicinity of the bubble as "mother" crystal. The generation of the microbubble induced Marangoni convection, the velocity of which reaches several hundreds of micrometers per second, crushing the first appearing chiral crystal into pieces by microfluidic shear. Namely, secondary nucleation caused by microfluidic shear amplified the number of "daughter" crystals with the same handedness. This spatiotemporally controllable micromixing experiment realized by laser irradiation gives us not only a novel route bridging a light and chiral symmetry breaking but also the novel method to observe the early stage dynamics of the secondary nucleation, which was hard to observe by conventional observation technique, in real time.
Optical vortex pumped solid-state Raman laser
(2017-01-01)
Nishigata, Yoshihiro
;
Lee, Cheng-Yeh
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Miyamoto, Yuji
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Miyamoto, Katsuhiko
;
Chen, Yung-Fu
A vortex Raman laser pumped by the second-order optical vortex mode was demonstrated. The first-and the second-Stokes waves that lased at the first-order optical vortex mode were generated. Considering the spatial intensity overlap between the pump and the first-Stokes beam, and between the first-and second-Stokes beams, the generation of a topological charge of 1 in the Stokes fields could be theoretically predicted.
Plasmonic Heating-Assisted Laser-Induced Crystallization from a NaCIO3 Unsaturated Mother Solution
(2017-02)
Niinomi, Hiromasa
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Sugiyama, Teruki
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Tagawa, Miho
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Maruyama, Mihoko
;
Ujihara, Toni
We provide a novel laser-induced crystallization mechanism which explains crystallization induced by visible laser trapping of silver nanoparticles (AgNPs) at the air/unsaturated mother solution interface from the focal spot [Niinomi et al.CrystEngComm 2016, 18, 7441-7448]. Simultaneous in situ microscopic observation of Raman scattering and polarized-light image revealed that the optical trapping of nanoparticles that exhibit surface-enhanced Raman scattering (SERS) triggers the crystallization, showing the excitation of localized surface plasmon resonance (LSPR) significantly promotes the crystallization. Numerical analysis of temperature distribution based on the combination of finite-difference time-domain electromagnetic and finite-difference heat transfer calculations shows that temperature reaches 390 degrees C at the focal spot because of plasmonic heating, the energy dissipation of the plasmon-enhanced electromagnetic field as heat. A conceivable mechanism of the crystallization is local increment of supersaturation caused by local solvent evaporation via the Plasmonic heating. This plasmonic heating assisted laser-induced nucleation process has the possibility to provide not only a novel approach for spatiotemporal control of crystallization but also a novel nucleation field based on nonlinear light matter interaction originating from the plasmon-enhanced electromagnetic near field through heterogeneous nucleation on the surface of plasmonic particles.
Plasmonic Manipulation of Sodium Chlorate Chiral Crystallization: Directed Chirality Transfer via Contact-Induced Polymorphic Transformation and Formation of Liquid Precursor
(2020-08-05)
Niinomi, Hiromasa
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Sugiyama, Teruki
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Tagawa, Miho
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Ujihara, Toru
;
Omatsu, Takashige
The control of crystallization not only impacts the production of functional crystalline materials or pharmaceuticals but also provides profit to investigate the fundamental mechanism of crystallization. Recently, we have revealed that plasmonic optical tweezers (POT) can "manipulate" the crystallization of a pharmaceutical compound from its aqueous solution by optically trapping molecular clusters, offering a novel strategy to control crystallization. Here we report a variety of unique crystallization phenomena by applying POT to sodium chlorate (NaClO3) chiral crystallization from an aqueous microdroplet loaded on a plasmonic substrate. Plasmon excitation significantly promotes crystallization intermediated by an achiral metastable crystal as a precursor. Also, the direction of the creeping of the resulting chiral crystal can be controlled. By utilizing this phenomenon, we achieved the directed chirality transfer from the chiral crystal to the achiral crystal via a forced contact-induced polymorphic transformation by intentionally making creeping chiral crystal contact with an achiral crystal. Moreover, we captured, by in situ optical microscopic observation, a liquid precursor that intermediates the NaClO3 achiral crystallization for the first time. Our results highlight the plasmonic manipulation of crystallization opening a new door not only to control crystallization but also to investigate the unprecedented fundamental process of crystallization.
Plasmonic Manipulation-Controlled Chiral Crystallization of Sodium Chlorate
(2020-06-04)
Cheng, An-Chieh
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Niinomi, Hiromasa
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Omatsu, Takashige
;
Ishida, Shutaro
;
Sasaki, Keiji
Plasmonic manipulation using well-designed triangular trimeric gold nanostructures achieves a giant (greater than 50%) crystal enantiomeric excess (CEE) of sodium chlorate (NaClO3). Stronger asymmetric interactions between molecule and light are pursued to reach high enantiomeric excess. The well-designed gold nanostructures immersed in a saturated NaClO3 D2O solution were irradiated with linear, left-hand, and right-hand circular polarizations of a 1064 nm continuous-wave laser. Within seconds of the start of the irradiation, an achiral metastable crystal was formed at the laser focus, and further irradiation induced a subsequent polymorphic transition to the chiral crystal. The crystal chirality is sensitive to the handedness of circular polarization, allowing for efficient enantioselectivity. The mechanisms to achieve this giant CEE are proposed based on the results of electromagnetic field analysis generated near the nanostructure by the finite element method.
Plasmonic Trapping-Induced Crystallization of Acetaminophen
(2019-02-01)
Niinomi, Hiromasa
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Sugiyama, Teruki
;
Uda, Satoshi
;
Tagawa, Miho
;
Ujihara, Toni
We demonstrate that plasmonic trapping can control crystallization of acetaminophen from its aqueous solution. Irradiation of a focused continuous-wave near-infrared laser to a plasmonic Au nanolattice supporting a thin film of a saturated solution allowed acetaminophen molecules to crystallize in annular distribution with the center of the focal spot. The annularly distributed crystals can be spatially manipulated by changing the position of the laser focal spot. The annular pattern is rationalized by competition between electrical field gradient force as an attractive force to the focal spot and thermophoretic force as a repulsive force. It is also found that, upon stopping the laser irradiation, the crystals first transformed to highly concentrated droplets rather than directly dissolving to the solution. Relaxation of the droplets by self-diffusion to the solution followed to the crystal/droplet transformation. These two-step dissociation dynamics indicate that not only plasmonic trapping of the molecules but also the enhanced electrical field by surface plasmon contributes to drive the crystallization, and it has a possibility to show the reverse process of the two-step nucleation model. Our demonstration highlights the possibility that plasmonic trapping by designed near-field and temperature distribution can manipulate not only molecular assembly but also creation of functional crystalline materials in nanoscale.