Observation of Terahertz Spin Hall Conductivity Spectrum in GaAs with Optical Spin Injection.

We report the first observation of the spin Hall conductivity spectrum in GaAs at room temperature. Our terahertz polarimetry with a precision of several µrads resolves the Faraday rotation of terahertz pulses arising from the inverse spin Hall effect of optically injected spin-polarized electrons. The obtained spin Hall conductivity spectrum exhibits an excellent quantitative agreement with theory, demonstrating a crossover in the dominant origin from impurity scattering in the dc regime to the intrinsic Berry-curvature mechanism in the terahertz regime. Our spectroscopic technique opens a new pathway to analyze anomalous transports related to spin, valley, or orbital degrees of freedom.

Highly CEP-stable optical parametric amplifier at 2†µm with a few-cycle duration and 100 kHz repetition rate.

We develop a BiB3O6 (BiBO)-based optical parametric amplifier in the spectral region around 2 µm using a Yb:KGW amplifier operating at 100 kHz. The two-stage degenerate optical parametric amplification results in a typical output energy of 30 µJ after compression, spectrum covering 1.7-2.5 µm range, and a pulse duration fully compressible down to 16.4 fs, corresponding to 2.3 cycles. Due to the inline difference frequency generation of the seed pulses, the carrier envelope phase (CEP) is passively stabilized without feedback over 11 hours at the level below 100 mrad including a long-term drift. Short-term statistical analysis in the spectral domain further shows a behavior qualitatively different from that of parametric fluorescence, indicating high degree of suppression of optical parametric fluorescence. The high phase stability together with the few-cycle pulse duration is promising for the investigation of high-field phenomena such as subcycle spectroscopy in solids or high harmonics generation.

Passively phase-locked Er:fiber source of single-cycle pulses in the near infrared with electro-optic timing modulation for field-resolved electron control.

A single-cycle light source in the near infrared is demonstrated enabling sensitive applications of ultrafast optical field control of electronic transport. The compact Er:fiber system generates passively phase-locked pulses with broadband spectra covering 150 THz to 350 THz at a duration of 4.2 fs and 40 MHz repetition rate. A second output arm is equipped with an electro-optic modulator (EOM) that switches the arrival time of the pulses by 700 ps at arbitrary frequencies up to 20 MHz, enabling timing modulation of the pump pulse without changing the average intensity. As a benchmark demonstration, we investigate the carrier relaxation dynamics in low-temperature-grown InGaAs (LT-InGaAs) using quantum interference currents (QuICs).

Ultrafast Control of Magnetic Anisotropy by Resonant Excitation of 4f Electrons and Phonons in Sm_{0.7}Er_{0.3}FeO_{3}.

We compare the ultrafast dynamics of the spin reorientation transition in the orthoferrite Sm_{0.7}Er_{0.3}FeO_{3} following two different pumping mechanisms. Intense few-cycle pulses in the midinfrared selectively excite either the f-f electronic transition of Sm^{3+} or optical phonons. With phonon pumping, a finite time delay exists for the spin reorientation, reflecting the energy transfer between the lattice and 4f system. In contrast, an instantaneous response is found for resonant f-f excitation. This suggests that 4f electronic pumping can directly alter the magnetic anisotropy due to the modification of 4f-3d exchange at femtosecond timescales, without involving lattice thermalization.

Ultrastructure of Hirschmanniella diversa early-stage infection in browning rhizomes of Indian lotus.

Browning rhizome (also known as "browning tuber disease") in Indian lotus (Nelumbo nucifera) caused by the nematode Hirschmanniella diversa is an emerging agronomic problem. In this study, the authors documented the early infection processes of H. diversa in the apices of young rhizomes of Indian lotus by electron microscopy analysis using an artificial inoculation method. Nematodes were attracted to young rhizome apices, invading them via narrow indentations by 4.5 hr after inoculation. Host cells adjacent to the cavity around the invading nematodes were absent and appeared to have disintegrated during infestation. Following contact with the nematodes, host cell walls and cellular contents became electron-dense and less defined, likely due to digestive enzymes secreted by the invading nematodes. Nematodes invaded to a depth of about 1 mm by 24 hr after inoculation, but did not penetrate the plant any further vertically, similar to the observation of browning in mature rhizomes in the field. The authors propose that the invasion sites of young rhizome apices become blackish-brown blotches as rhizomes mature in the field due to oxidation.Browning rhizome (also known as "browning tuber disease") in Indian lotus (Nelumbo nucifera) caused by the nematode Hirschmanniella diversa is an emerging agronomic problem. In this study, the authors documented the early infection processes of H. diversa in the apices of young rhizomes of Indian lotus by electron microscopy analysis using an artificial inoculation method. Nematodes were attracted to young rhizome apices, invading them via narrow indentations by 4.5 hr after inoculation. Host cells adjacent to the cavity around the invading nematodes were absent and appeared to have disintegrated during infestation. Following contact with the nematodes, host cell walls and cellular contents became electron-dense and less defined, likely due to digestive enzymes secreted by the invading nematodes. Nematodes invaded to a depth of about 1 mm by 24 hr after inoculation, but did not penetrate the plant any further vertically, similar to the observation of browning in mature rhizomes in the field. The authors propose that the invasion sites of young rhizome apices become blackish-brown blotches as rhizomes mature in the field due to oxidation.

Reconfiguration of magnetic domain structures of ErFeO3 by intense terahertz free electron laser pulses.

Understanding the interaction between intense terahertz (THz) electromagnetic fields and spin systems has been gaining importance in modern spintronics research as a unique pathway to realize ultrafast macroscopic magnetization control. In this work, we used intense THz pulses with pulse energies in the order of 10 mJ/pulse generated from the terahertz free electron laser (THz-FEL) to irradiate the ferromagnetic domains of ErFeO3 single crystal. It was found that the domain shape can be locally reconfigured by irradiating the THz - FEL pulses near the domain boundary. Observed domain reconfiguration mechanism can be phenomenologically understood by the combination of depinning effect and the entropic force due to local thermal gradient exerted by terahertz irradiation. Our finding opens up a new possibility of realizing thermal-spin effects at THz frequency ranges by using THz-FEL pulses.

Enhancing terahertz magnetic near field induced by a micro-split-ring resonator with a tapered waveguide.

Substantial enhancement of terahertz magnetic near field achieved by the combination of a tapered metallic waveguide and a micro-split-ring resonator is demonstrated. The magnetic near field is probed directly via the magneto-optic sampling with a Tb3Ga5O12 crystal. The incident terahertz wave with a half-cycle waveform is generated by using the pulse-front tilting method. The magnetic near field at the resonant frequency is enhanced by more than 30 times through the combination of the waveguide and the resonator. The peak amplitude of the magnetic field with a damped oscillation waveform in the time domain is up to 0.4 T. The resonant frequency can be tuned by adopting different resonator designs. The mechanism of the enhancement is analyzed by performing calculations based on the finite element method. The strong terahertz magnetic near field enables the excitation of large-amplitude spin dynamics and can be utilized for an ultrafast spin control.

Macroscopic Magnetization Control by Symmetry Breaking of Photoinduced Spin Reorientation with Intense Terahertz Magnetic Near Field.

We exploit an intense terahertz magnetic near field combined with femtosecond laser excitation to break the symmetry of photoinduced spin reorientation paths in ErFeO_{3}. We succeed in aligning macroscopic magnetization reaching up to 80% of total magnetization in the sample to selectable orientations by adjusting the time delay between terahertz and optical pump pulses. The spin dynamics are well reproduced by equations of motion, including time-dependent magnetic potential. We show that the direction of the generated magnetization is determined by the transient direction of spin tilting and the magnetic field at the moment of photoexcitation.

Coherent field transients below 15 THz from phase-matched difference frequency generation in 4H-SiC.

We experimentally demonstrate tunable, phase-matched difference frequency generation covering the spectral region below 15 THz using 4H-SiC as a nonlinear crystal. This material combines a non-centrosymmetric lattice and strong birefringence with broadband transparency at low optical frequencies. Thorough refractive index measurements in the terahertz spectral range allow us to calculate phase-matching conditions for any near-infrared pump laser source. 4H-SiC is also exploited as a detector crystal for electro-optic sampling. The results allow us to estimate the effective second-order nonlinear coefficient.

Coherent Two-Dimensional Terahertz Magnetic Resonance Spectroscopy of Collective Spin Waves.

We report a demonstration of two-dimensional (2D) terahertz (THz) magnetic resonance spectroscopy using the magnetic fields of two time-delayed THz pulses. We apply the methodology to directly reveal the nonlinear responses of collective spin waves (magnons) in a canted antiferromagnetic crystal. The 2D THz spectra show all of the third-order nonlinear magnon signals including magnon spin echoes, and 2-quantum signals that reveal pairwise correlations between magnons at the Brillouin zone center. We also observe second-order nonlinear magnon signals showing resonance-enhanced second-harmonic and difference-frequency generation. Numerical simulations of the spin dynamics reproduce all of the spectral features in excellent agreement with the experimental 2D THz spectra.

The Feeding Behavior of Adult Root-knot Nematodes (Meloidogyne incognita) in Rose Balsam and Tomato.

Meloidogyne incognita is a parasitic root-knot nematode that causes considerable yield loss in a wide range of plants. In this study we documented the movement of adult female nematodes for more than 2 hr in micro-slices of infected tomato (Solanum lycopersicum) and rose balsam (Impatiens balsamina) plants using light and video microscopy. Stylet thrusting was followed by short pumping actions of the esophagus, dorsal esophageal gland ampulla, and metacorpal bulb. Regular thrusting was normally accompanied by head turning and always preceded continuous stylet thrusting aimed at a single point (for 20 to 90 sec). Females often held the stylet in a protruded position, while pulsating the metacorpus bulb, for about 30 sec. Subsequently, the stylet was paused in a retracted position for 5 to 40 sec. This sequence of behavior took 290 to 380 sec to complete. The procedure developed in this study provides a useful cytological technique to investigate the interaction between root-knot nematodes and the giant cells formed by infected plants. Scanning electron microscopy revealed that the head of the adult nematode was located in the narrow intercellular spaces among several giant cells. The anterior part of the head of the adult was folded like a concertina, whereas that of the second-stage juvenile was not. The labial disc and medial lips of second-stage juveniles seemed expanded and sturdy, whereas those of the adult were star-shaped, appeared to be contracted, and softer. These morphological differences in the heads of adult and second-stage juveniles are discussed with respect to their movement.

Terahertz time-domain observation of spin reorientation in orthoferrite ErFeO3 through magnetic free induction decay.

Terahertz time domain spectroscopy was performed on orthoferrite ErFeO3. Through the emission from the two magnetic resonance modes, we succeeded in observing the spin reorientation transition. Depending on the orientation of the single crystal, the reorientation can be detected as either mode switching between the two modes or polarization change of the emission. This method enables picosecond resolved observation of the reorientation without disturbances such as electronic excitation and heating, and it is expected to open the doorway to observe ultrafast reorientation with the terahertz pulse.

Speckle-free, shaded 3D images produced by computer-generated holography.

A hologram display technique that provides speckle-free, shaded reconstructed images is proposed. A three-dimensional object consists of object points; these object points are divided into plural object point groups that are generated in a time-sequential manner. Each object point group consists of a two-dimensional (2D) array of object points that are separated so as to prevent interference among them. Each object point group is generated by displaying a 2D array of zone plates on a high-speed spatial light modulator (SLM). The amplitude distribution of the zone plates is modulated two-dimensionally based on Phong shading to shade the reconstructed images. The 2D amplitude distribution of the zone plates is decomposed into multiple binary patterns that are displayed by the SLM in a time-sequential manner. The proposed method is experimentally verified.

Analysis of the amino acid residues involved in the thermal properties of the monomeric isocitrate dehydrogenases of the psychrophilic bacterium Colwellia maris and the mesophilic bacterium Azotobacter vinelandii.

Cold-adapted monomeric isocitrate dehydrogenase of a psychrophilic bacterium, Colwellia maris, (CmIDH) showed a high degree of amino acid sequential identity (69.5%) to a mesophilic nitrogen-fixing bacterium, Azotobacter vinelandii, (AvIDH). In this study, three Ala residues of CmIDH and the corresponding Pro residues of AvIDH were exchanged by site-directed mutagenesis, and several properties of single, double, and triple mutants of the two enzymes were investigated. The mutated CmIDHs, which replaced Ala719 with Pro, showed increased activity and elevation of the optimum temperature and thermostability for activity. In contrast, mutants of AvIDH, in which Pro717 was replaced by Ala, decreased the thermostability for activity. These results indicate that Ala719 of CmIDH and Pro717 of AvIDH are involved in thermostability. On the other hand, mutated CmIDH, in which Ala710 was replaced by Pro, and the corresponding AvIDH mutant, which replaced Pro708 with Ala, showed higher and lower specific activity than the corresponding wild-type enzymes, suggesting that Pro708 of AvIDH is involved in its high catalytic ability. Furthermore, the exchange mutations between Ala740 in CmIDH and the corresponding Pro738 in AvIDH resulted in decreased and increased thermostability for CmIDH and AvIDH activity respectively, suggesting that the native Ala740 and Pro738 residues make the enzymes thermostable and thermolabile.

Shading of a computer-generated hologram by zone plate modulation.

We propose a hologram calculation technique that enables reconstructing a shaded three-dimensional (3D) image. The amplitude distributions of zone plates, which generate the object points that constitute a 3D object, were two-dimensionally modulated. Two-dimensional (2D) amplitude modulation was determined on the basis of the Phong reflection model developed for computer graphics, which considers the specular, diffuse, and ambient reflection light components. The 2D amplitude modulation added variable and constant modulations: the former controlled the specular light component and the latter controlled the diffuse and ambient components. The proposed calculation technique was experimentally verified. The reconstructed image showed specular reflection that varied depending on the viewing position.

Rice WRKY45 plays important roles in fungal and bacterial disease resistance.

Plant 'activators', such as benzothiadiazole (BTH), protect plants from various diseases by priming the plant salicylic acid (SA) signalling pathway. We have reported previously that a transcription factor identified in rice, WRKY45 (OsWRKY45), plays a pivotal role in BTH-induced disease resistance by mediating SA signalling. Here, we report further functional characterization of WRKY45. Different plant activators vary in their action points, either downstream (BTH and tiadinil) or upstream (probenazole) of SA. Rice resistance to Magnaporthe grisea, induced by both types of plant activator, was markedly reduced in WRKY45-knockdown (WRKY45-kd) rice, indicating a universal role for WRKY45 in chemical-induced resistance. Fungal invasion into rice cells was blocked at most attempted invasion sites (pre-invasive defence) in WRKY45-overexpressing (WRKY45-ox) rice. Hydrogen peroxide accumulated within the cell wall underneath invading fungus appressoria or between the cell wall and the cytoplasm, implying a possible role for H(2)O(2) in pre-invasive defence. Moreover, a hypersensitive reaction-like reaction was observed in rice cells, in which fungal growth was inhibited after invasion (post-invasive defence). The two levels of defence mechanism appear to correspond to Type I and II nonhost resistances. The leaf blast resistance of WRKY45-ox rice plants was much higher than that of other known blast-resistant varieties. WRKY45-ox plants also showed strong panicle blast resistance. BTH-induced resistance to Xanthomonas oryzae pv. oryzae was compromised in WRKY45-kd rice, whereas WRKY45-ox plants were highly resistant to this pathogen. However, WRKY45-ox plants were susceptible to Rhizoctonia solani. These results indicate the versatility and limitations of the application of this gene.

Improving viewing region of 4f optical system for holographic displays.

A 4f optical system with a single-sideband filter has been used for electronic holographic displays in order to obtain a reconstructed image without a conjugate image and zero-order diffraction light. However, the viewing region is inclined, and the viewing region in which an entire reconstructed image can be viewed is limited. In the present study, one of the Fourier transform lenses constituting the 4f optical system is shifted to correct the viewing region inclination. Moreover, a screen lens is added in the image plane of the 4f optical system to maximize the viewing region. The inclination of the viewing region can also be corrected by shifting the screen lens instead of shifting the Fourier transform lens. Experimental verifications of these corrections are described.

Comparative study of hydrophilic and hydrophobic ionic liquids for observing cultured human cells by scanning electron microscopy.

An ionic liquid (IL) is a salt that remains in the liquid state at room temperature. It does not vaporize under vacuum and imparts electrical conductivity to samples for observation by scanning electron microscopy (SEM). Recently, the usefulness of ILs has been widely recognized. In our previous study, one of the ILs 1-ethyl-3-methylimidazolium tetrafluoroborate (EtMelm(+) BF(4)(-)) was used for SEM analysis of biological samples. In comparison with the conventional method, samples prepared using EtMelm(+) BF(4)(-) provided more detailed SEM images of the cell ultrastructure, enabling the observation of protrusions. In addition, the IL treatment is a less time consuming and simple method that does not include dehydration, drying, and conductivity treatments, which are an essential parts of the conventional method. In this study, we compared the usefulness of four hydrophobic and three hydrophilic ILs for SEM to observe fixed cultured human A549 cells. All ILs worked well to prevent "charge-up" effect for SEM observation. However, the hydrophilic ILs tended to provide clearer images than the hydrophobic ILs. We concluded that various ILs can be used for SEM sample preparation and their application to a wide range of fields is anticipated in future.

Ionic liquid enables simple and rapid sample preparation of human culturing cells for scanning electron microscope analysis.

Ionic liquid is a kind of salt that stays in a molten state even at room temperature. It does not vaporize at all in vacuum and facilitates electrical conductivity to the sample surfaces for observations with a scanning electron microscope (SEM). In this study, we used an ionic liquid in SEM for the first time to observe fixed human culture cells. The condition for the cell culture using wrapping sheets and SEM settings were varied to elucidate the optimized protocol. Compared to samples prepared by the conventional way, the ionic liquid-treatment of samples gave SEM images of the cellular ultra structures in more detail, enabling observation of microvilli that made bridges between separated cells. In addition, the ionic liquid treatment is less time consuming as well as less laborious compared with the conventional way that includes dehydration, drying, and conductivity treatments. Totally, we concluded the ionic liquid is a useful reagent for SEM sample preparation.

Immunocytochemical approach for surface layer proteins of freeze-substituted Tannerella forsythensis by energy-filtering transmission electron microscopy.

Tannerella forsythensis (Bacteroides forsythus), an anaerobic gram-negative potential periodontal pathogens in the progression of periodontitis. IT forsythensis has unique bacterial protein profiles containing major proteins with apparent molecular weight of more than 200-kDa shown by sodium dodecylsulfate-polyacrylamide gel electrophoresis. It is also known to have a typical surface layer (S-layer) consisting of regularly arrayed subunits outside the outer membrane revealed by electron microscopy. On the other hand, electron microscopy showed that the best preservation of structure was obtained when cells were postfixed with OsO4, but this resulted in very low levels of gold particles labeling. Therefore, cells were applied to pieces of filter paper and freeze-substituted by plung-freezing in Liquid propane, substituted in methanol containing 0.5% uranyl acetate, and infiltrated with LR-White resin. We also examined the relation between high molecular weight proteins and S-layer in energy-filtering transmission electron microscopy (EF-TEM) to visualize 3,3'-diaminobenzidene, tetrahydrochloride (DAB) reaction. The three-window method in electron spectroscopic images (ESI) of nitrogen (N) element, reflecting the presence of DAB moieties by the DAB reaction solution, horseradish peroxidase (HRP)-conjugated secondary antibodies instead of immunogold particles obtained by the EF-TEM. The mapping patterns of net N element were restricted to the outermost cell surface.