Publications

@article{tate2019,

title = {Visible light-induced thymine dimerisation based on large localised field gradient by non-uniform optical near-field},

author = {Naoya Tate and Takashi Yatsui},

doi = {10.1038/s41598-019-54661-6},

year  = {2019},

date = {2019-12-01},

journal = {Scientific Reports},

volume = {9},

pages = {18383},

publisher = {Springer Nature},

abstract = {The localised excitations of several molecular reactions utilising optical irradiation have been studied in the field of molecular physics. In particular, deoxyribonucleic acid (DNA) strands organise the genetic information of all living matter. Therefore, artificial methods for freely controlling reactions using only light irradiation are highly desirable for reactions of these strands; this in regard with artificial protein synthesis, regional genetic curing, and stochastic analysis of several genetic expressions. Generally, DNA strands have strong absorption features in the deep ultra-violet (DUV) region, which are related to the degradation and reconstruction of the strand bonding structures. However, irradiation by DUV light unavoidably induces unintended molecular reactions which can damage and break the DNA strands. In this paper, we report a photo-induced molecular reaction initiated by the irradiation of DNA strands with visible light. We utilised photo-dissociation from the vibrational levels induced by non-uniform optical near-fields surrounding nanometric Au particles to which DNA strands were attached. The results were experimentally observed by a reduction in the DUV absorbance of the DNA strands during irradiation. There was a much higher yield of molecular reactions than expected due to the absorbance of visible light, and no defects were caused in the DNA strands.},

keywords = {DNA, Near-field effect, Non-uniform optical near field},

pubstate = {published},

tppubtype = {article}

}

@article{YATSUI2017166,

title = {Nano-scale chemical reactions based on non-uniform optical near-fields and their applications},

author = {Takashi Yatsui and Maiku Yamaguchi and Katsuyuki Nobusada},

doi = {10.1016/j.pquantelec.2017.06.001},

issn = {0079-6727},

year  = {2017},

date = {2017-09-01},

journal = {Progress in Quantum Electronics},

volume = {55},

pages = {166 - 194},

abstract = {Interaction between light and materials is essential in the physics underlying all optical devices, including light emitting devices such as light emitting diodes and lasers, photo-voltaic devices, and photo-synthesis systems. The demand for higher light utilization efficiency is becoming increasingly important for advanced optical devices. This is because, when feature size is smaller than the incident light wavelength, photons cannot couple with devices efficiently. In this paper, we review recent progress regarding a unique phenomenon at the nano scale and its applications. First, we summarize the development of light–matter interactions at the nano-scale. Second, we review recent theoretical works focusing on optical near fields in which unique phenomena arise from non-uniform optical fields. We then review several recent developments based on the near-field effect, including artificial photosynthesis and near-field etching for realization of angstrom-scale fattened surfaces. Finally, we discuss the future outlook for these technologies.},

note = {review article},

keywords = {Artificial photosynthesis, First, Near-field etching, Non-uniform optical near field, Photodissociation path with two-step excitation, Review, Selected, SHG},

pubstate = {published},

tppubtype = {article}

}

@article{PhysRevA.92.043809,

title = {Nonlinear optical response induced by a second-harmonic electric-field component concomitant with optical near-field excitation},

author = {Maiku Yamaguchi and Katsuyuki Nobusada and Takashi Yatsui},

doi = {10.1103/PhysRevA.92.043809},

year  = {2015},

date = {2015-10-01},

journal = {Phys. Rev. A},

volume = {92},

number = {4},

pages = {043809},

publisher = {American Physical Society},

abstract = {Electron dynamics excited by an optical near field (ONF) in a two-dimensional quantum dot model was investigated by solving a time-dependent Schrödinger equation. It was found that the ONF excitation of the electron caused two characteristic phenomena: a two-photon absorption and an induction of a magnetic dipole moment with a strong third-harmonic component. By analyzing the interaction dynamics of the ONF and the electron, we explained that the physical mechanism underlying these phenomena was the second-harmonic electric-field component concomitant with the near-field excitation originating from the nonuniformity of the ONF. Despite a y-polarized ONF source, the second-harmonic component of an 

x-polarized electric field was inherently generated. The effect of the second-harmonic electric-field component is not due to usual second-order nonlinear response but appears only when we explicitly consider the electron dynamics interacting with the ONF beyond the conventional optical response assuming the dipole approximation.},

keywords = {Non-uniform optical near field, Selected, SHG},

pubstate = {published},

tppubtype = {article}

}

@article{2015SHG,

title = {Two-photon absorption induced by electric field gradient of optical near-field and its application to photolithography},

author = {Maiku Yamaguchi and Katsuyuki Nobusada and Tadashi Kawazoe and Takashi Yatsui},

doi = {10.1063/1.4921005},

year  = {2015},

date = {2015-05-01},

journal = {Applied Physics Letters},

volume = {106},

number = {19},

pages = {191103},

abstract = {An electric field gradient is an inherent property of the optical near-field (ONF). We investigated its effect on electron excitation in a quantum dot via model calculations combining a density matrix formalism and a classical Lorentz model. The electric field gradient of the ONF was found to cause two-photon absorption by an unusual mechanism. Furthermore, the absorption exhibits a nonmonotonic dependence on the spatial arrangement of the nanosystem, completely different from that of conventional two-photon absorption induced by an intense electric field. The present two-photon absorption process was verified in a previous experimental observation by reinterpreting the results of ONF photolithography.},

keywords = {Nanophotonic fabrication, Non-uniform optical near field, SHG},

pubstate = {published},

tppubtype = {article}

}

@article{2014YatsuiGaAsAPA,

title = {Emission from a dipole-forbidden energy state in a GaAs quantum-ring induced by dressed photon},

author = {Takashi Yatsui and Wataru Nomura and Takaaki Mano and Hideki Miyazaki and Kazuaki Sakoda and Tadashi Kawazoe and Motoichi Ohtsu},

doi = {10.1007/s00339-013-7905-y},

year  = {2014},

date = {2014-04-01},

journal = {Applied Physics A},

volume = {115},

number = {1},

pages = {1-4},

publisher = {Springer Nature},

abstract = {The emission intensity from the dipole-forbidden state in a GaAs quantum-ring was increased via close proximity with an aperture fiber probe to induce a near-field interaction between the probe apex and the quantum-ring. As a result, a significant decrease was observed in the decay time of the emission from a dipole-forbidden energy state.},

keywords = {First, GaAs, Non-uniform optical near field, Quantum-ring},

pubstate = {published},

tppubtype = {article}

}

@article{2014water,

title = {Dressed-photon–phonon (DPP)-assisted visible- and infrared-light water splitting},

author = {Takashi Yatsui and Tsubasa Imoto and Takahiro Mochizuki and Kokoro Kitamura and Tadashi Kawazoe},

doi = {10.1038/srep04561},

year  = {2014},

date = {2014-04-01},

journal = {Scientific Reports},

volume = {4},

pages = {4561},

publisher = {Springer Nature},

abstract = {A dressed-phonon–phonon (DPP) assisted photocatalyst reaction was carried out to increase the visible light responsibility, where the photon energy of the radiation, which ranged from visible to infrared light is less than band gap energy of the photocatalyst (ZnO, 3.3 eV). The dependence of the photocurrent on excitation power indicated that two-step excitation occurred in DPP-assisted process. A cathodoluminescence measurement also supported the conclusion that the visible- and infrared-light excitation originated from DPP excitation, not from defect states in the ZnO nanorod photocatalyst.},

keywords = {First, Non-uniform optical near field, Water splitting, ZnO},

pubstate = {published},

tppubtype = {article}

}

@article{2013nabilaSR,

title = {CO2 phonon mode renormalization using phonon-assisted energy up-conversion},

author = {Nabila Tanjeem and Tadashi Kawazoe and Takashi Yatsui},

doi = {10.1038/srep03341},

year  = {2013},

date = {2013-11-01},

journal = {Scientific Reports},

volume = {3},

pages = {3341},

publisher = {Springer Nature},

abstract = {Molecular dissociation under incident light whose energy is lower than the bond dissociation energy has been achieved through multi step excitation using a coupled state of a photon, electron and multimode-coherent phonon as known as the dressed photon phonon (DPP). Here, we have investigated the effects of the DPP on CO2, a very stable molecule with high absorption and dissociation energies, by introducing ZnO nanorods to generate the DPP. Then, the changes in CO2 absorption bands were evaluated using light with a wavelength longer than the absorption wavelength, which confirmed the DPP-assisted energy up-conversion. To evaluate the specific CO2 modes related to this process, we measured the CO2 vibration-rotation spectra in the near-infrared region. Detailed analysis of the 3ν3 vibrational band when a DPP source is present showed that DPP causes a significant increase in the intensity of certain absorption bands, especially those that require higher energies to activate.},

keywords = {CO2 reduction, Non-uniform optical near field},

pubstate = {published},

tppubtype = {article}

}

@article{10.1117/1.JNP.7.073796,

title = {Phonon-assisted near-field activation of electron transfer},

author = {Takashi Yatsui and Kazaunori Iijima and Tsubasa Imoto and Kokoro Kitamura and Tadashi Kawazoe},

doi = {10.1117/1.JNP.7.073796},

year  = {2013},

date = {2013-09-01},

journal = {Journal of Nanophotonics},

volume = {7},

number = {1},

pages = {1 -- 8},

publisher = {SPIE},

abstract = {An optical near field should promote phonon-assisted multiple excitation in nanoscale structures. With the phonon-assisted process, greater catalytic activity is expected without heating. To confirm this effect, photo-induced current generation using platinum black electrodes in ferricyanide solution (an absorption band-edge wavelength of 470 nm) under visible light irradiation continuous wave [(CW), λ=532  nm ] was observed. Higher order dependence of the generated current density on the incident light power was observed, indicating two-step activation of electron transfer, which originated from the phonon-assisted near-field effect on the nanostructured surface of the electrode.},

keywords = {Absorption, Electrodes, First, Nanostructuring, Non-uniform optical near field, Platinum, sapphire},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1063/1.3090491,

title = {Nanophotonic energy up conversion using ZnO nanorod double-quantum-well structures},

author = {Takashi Yatsui and Suguru Sangu and Kiyoshi Kobayashi and Tadashi Kawazoe and Motoichi Ohtsu and Jinkyoung Yoo and Gyu-Chul Yi},

url = {https://doi.org/10.1063/1.3090491},

doi = {10.1063/1.3090491},

year  = {2009},

date = {2009-02-01},

journal = {Applied Physics Letters},

volume = {94},

number = {8},

pages = {083113},

abstract = {We report on near-field spectroscopy of ZnO/ZnMgO nanorod double-quantum-well structures (DQWs) for a nanometer-scale photonic device. We observed energy up conversion assisted by the absorption of phonons generated in the ZnO nanorod DQWs. Theoretical calculation of the coherent excitonic excitation of the population with incoherent phonon coupling agrees well with the obtained experimental power dependence of the up conversion efficiency. It should result in an increase in the efficiency of devices, such as photodetectors, solar cells, and so on.},

keywords = {First, nanorod, Non-uniform optical near field, ZnO},

pubstate = {published},

tppubtype = {article}

}

@article{10.1117/1.2794355,

title = {Near-field components and evaluation of photoluminescence in silicon nanostructures},

author = {Takashi Yatsui and Tadashi Kawazoe and Kiyoshi Kobayashi and Motoichi Ohtsu},

doi = {10.1117/1.2794355},

year  = {2007},

date = {2007-09-01},

journal = {Journal of Nanophotonics},

volume = {1},

number = {1},

pages = {011570},

publisher = {SPIE},

abstract = {Using illumination-collection mode optical near-field spectroscopy, a a spectral shift of photoluminescence of silicon (Si) nanocrystals compared with the far-field measurement was observed, due to the near-field coupling of the Si nanocrystals and the probe.},

keywords = {First, Non-uniform optical near field, Si, silicon},

pubstate = {published},

tppubtype = {article}

}