47 research outputs found
Static magnetic order in NaCoO detected by muon spin rotation and relaxation
The nature of the magnetic transition of the Na-rich thermoelectric
NaCoO at 22K was studied by positive muon-spin-rotation and
relaxation (SR) spectroscopy, using a polycrystalline sample in the
temperature range between 300 and 2.5 K. Zero field SR measurements
indicated the existence of a static internal magnetic field at temperatures
below 22 K (= ). The observed muon spin precession signal below
consisted of three components with different precession
frequencies, corresponding to three inequivalent muon sites in the
NaCoO lattice. The total volume fraction of the three components
was estimated as 21% at 2.5 K; thus, this magnetic transition was not
induced by impurities but is an intrinsic change in the magnetism of the
sample, although the sample was magnetically inhomogeneous otherwise. On the
other hand, a similar experiment on a NaCoO sample exhibited no
magnetic transition down to 2.5 K; which indicates that the average valence of
the Co ions is responsible for inducing the magnetic transition at 22 K.Comment: 5 pages, 4 figures, Phys. Rev. B 68 (2003) in pres
Growth Enhancement of Organic Nonlinear Optical Crystals by Femtosecond Laser Ablation
Takahashi H., Yamaji M., Ikeyama J., et al. Growth Enhancement of Organic Nonlinear Optical Crystals by Femtosecond Laser Ablation. Journal of Physical Chemistry C, 125(15), 8391-8397, 22 April 2021: © 2021 American Chemical Society. DOI: 10.1021/acs.jpcc.0c10636.The impact of femtosecond (fs) laser ablation on the shape and nonlinear optical (NLO) properties of organic crystals was investigated. fs laser ablation of a local region of a NLO crystal can selectively enhance the growth of targeted faces. Reflection imaging of crystal surfaces revealed that a number of new crystal steps are generated from ablated area, which induces the crystal growth enhancement. In addition, the evaluation of terahertz wave emission from ablated crystals shows that NLO properties are not deteriorated after fs laser ablation. We foresee that crystal shape control by such a damage-less ablation process will potentially improve the NLO properties of organic crystals
In situ reflection imaging and microspectroscopic study on three-dimensional crystal growth of L-phenylalanine under laser trapping
We investigate growth behavior of an L-phenylalanine crystal formed by laser trapping with the use of reflection imaging and microspectroscopy. Optical reflection micrographs show colored images of the crystal due to constructive interference of incident white light. The color distribution on the crystal is dynamically changed under laser trapping, which is in addition to enlargement of the crystal plane area. The temporal change in the crystal thickness is examined by measuring reflection spectra of the crystal. We discuss the three-dimensional crystal growth under laser trapping by comprehensively considering the changes in crystal thickness and crystal plane area. (C) 2019 The Japan Society of Applied Physic
Bubble generation and molecular crystallization at solution surface by intense continuous-wave laser irradiation
We demonstrate bubble generation outside the focus induced by irradiating a focused 1064 nm continuous-wave laser beam into the surface of water and L-phenylalanine H2O solutions. In the former case of water, bubbles stay at positions distant from the focus during the irradiation, and their size and location are controllable by the laser power. In the latter solution, bubbles move outward toward the surrounding area, and subsequently crystallization takes place at the focus. We discuss these behaviors from the viewpoints of the temperature elevation accompanying the decrease in air solubility as well as the optical trapping of L-phenylalanine clusters giving a single crystal. (C) 2018 The Japan Society of Applied Physic
Femtosecond Laser Trapping Dynamics of Nanoparticles: A Single Transient Assembly Formation Leading to Their Directional Ejection
© XXXX American Chemical Society. We investigated femtosecond laser trapping dynamics of silica nanoparticles with different hydrophobic surface properties. We demonstrated that the hydrophobic surface on the silica nanoparticles facilitates mutual association of the nanoparticles in the optical trapping site. Such association of optically trapped nanoparticles is a prerequisite to induce their directional ejection away from the trapping site. The directional ejection of the optically trapped nanoparticles is most probably due to asymmetric three-dimensional ejecting forces generated by the electromagnetic interaction between transient assembly in the focal spot and the incident pulses. These findings provide important insights into the directional ejection of nanoparticles from the trapping site in the femtosecond laser trapping, and this physicochemical phenomenon is controlled by both the trapping laser and material properties.status: publishe
Millimeter-Scale Dense Liquid Droplet Formation and Crystallization in Glycine Solution Induced by Photon Pressure
A millimeter-scale dense liquid droplet of glycine is prepared by focusing a CW near-infrared laser beam at the glass/solution interface of a thin film of its supersaturated heavy water solution. The formation process is investigated by direct observation with CCD and by measuring temporal change of the surface height with a displacement meter. The droplet becomes much larger than a focal spot size, a few mm width and ∼150 μm height, and observable with the naked eye. Interestingly, the droplet remains for a few tens of seconds even after switching off the laser beam. Whereas the droplet is kept during laser irradiation, the crystallization is immediately attained by shifting the laser beam to the air/droplet surface. It is considered that the droplet is possibly the early stage of the multistep crystallization process and plays an important role in photon pressure-induced crystallization of glycine
Laser Trapping and Crystallization Dynamics of l‑Phenylalanine at Solution Surface
We present laser trapping behavior of l-phenylalanine
(l-Phe) at a surface of its unsaturated aqueous solution
by a focused continuous-wave (CW) near-infrared (NIR) laser beam.
Upon the irradiation into the solution surface, laser trapping of
the liquid-like clusters is induced concurrently with local laser
heating, forming an anhydrous plate-like crystal at the focal spot.
The following laser irradiation into a central part of the plate-like
crystal leads to laser trapping at the crystal surface not only for l-Phe molecules/clusters but also for polystyrene (PS) particles.
The particles are closely packed at crystal edges despite that the
crystal surface is not illuminated by the laser directly. The molecules/clusters
are also gathered and adsorbed to the crystal surface, leading to
crystal growth. The trapping dynamics and mechanism are discussed
in view of optical potential formed at the crystal surface by light
propagation inside the crystal