Macroscopic Ionic Flow in a Superionic Conductor Na^{+} β-Alumina Driven by Single-Cycle Terahertz Pulses.

Ionic motion significantly contributes to conductivity in devices such as memory, switches, and rechargeable batteries. In our work, we experimentally demonstrate that intense terahertz electric-field transients can be used to manipulate ions in a superionic conductor, namely Na^{+} β-alumina. The cations trapped in the local potential minima are accelerated using single-cycle terahertz pulses, thereby inducing a macroscopic current flow on a subpicosecond timescale.

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 TbGaO crystal. The incident terahertz wave with a half-cycle waveform is generated by using the pulse-front tilting method.

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.

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.

Transient gain analysis of gain-switched semiconductor lasers during pulse lasing.

We analyzed the transient gain properties of three gain-switched semiconductor lasers with different materials and cavity structures during pulse lasing. All the semiconductor lasers were pumped with impulse optical pumping, and all the generated gain-switched output pulses were well described by exponential functions in their rise parts, wherein the transient gains were derived according to the rate-equation theoretical model. In spite of the different laser structures and materials, the results consistently demonstrated that a higher transient gain produces shorter output pulses, indicating the dominant role of higher transient gain in the generation of even shorter gain-switched pulses with semiconductor lasers.

Magnetic-excitation-assisted photoluminescence from self-trapped exciton states in MnO.

We examined the photoluminescence (PL) in single-crystal MnO(111) and observed a new strong emission band with a high-energy-side edge of 1.905 eV below 20 K. The emission bands with high-energy-side edges of 1.

Optically detecting the edge-state of a three-dimensional topological insulator under ambient conditions by ultrafast infrared photoluminescence spectroscopy.

Ultrafast infrared photoluminescence spectroscopy was applied to a three-dimensional topological insulator TlBiSe2 under ambient conditions. The dynamics of the luminescence exhibited bulk-insulating and gapless characteristics bounded by the bulk band gap energy. The existence of the topologically protected surface state and the picosecond-order relaxation time of the surface carriers, which was distinguishable from the bulk response, were observed.

Direct generation of 2-ps blue pulses from gain-switched InGaN VCSEL assessed by up-conversion technique.

Ultra-short pulses in blue region generated from compact and low-cost semiconductor lasers have attracted much attention for a wide variety of applications. Nitride-based vertical-cavity surface-emitting lasers (VCSELs), having intrinsic high material gain and short cavities, favor the generation of ultra-short blue pulses via a simple gain-switching technique. In this study, we fabricated a single-mode InGaN VCSEL consisting of 10-period InGaN/GaN quantum wells (QWs).

Spectral dynamics of picosecond gain-switched pulses from nitride-based vertical-cavity surface-emitting lasers.

Short pulses generated from low-cost semiconductor lasers by a simple gain-switching technique have attracted enormous attention because of their potential usage in wide applications. Therein, reducing the durations of gain-switched pulses is a key technical point for promoting their applications. Therefore, understanding the dynamic characteristics of gain-switched pulses is highly desirable.

Gain-switching dynamics in optically pumped single-mode InGaN vertical-cavity surface-emitting lasers.

The gain-switching dynamics of single-mode pulses were studied in blue InGaN multiple-quantum-well vertical-cavity surface-emitting lasers (VCSELs) through impulsive optical pumping. We measured the shortest single-mode pulses of 6.0 ps in width with a method of up-conversion, and also obtained the pulse width and the delay time as functions of pump powers from streak-camera measurements.

Probing of local structures of thermal and photoinduced phases in rubidium manganese hexacyanoferrate by resonant Raman spectroscopy.

Resonant couplings of the electronic states and the stretching vibrations of CN(-) ligands, which bridges metal ions, is investigated by resonance Raman spectroscopy for Rb(0.94)Mn[Fe(CN)6](0.98)·0.

Mechanism of enhanced optical second-harmonic generation in the conducting pyrochlore-type Pb2Ir2O7-x oxide compound.

The structural, electronic, and optical properties of pyrochlore-type Pb(2)Ir(2)O(6)O(0.55)('), which is a metal without spatial inversion symmetry at room temperature, were investigated. Structural analysis revealed that the structural distortion relevant to the breakdown of the inversion symmetry is dominated by the Pb-O' network but is very small in the Ir-O network.

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.

Experimental verification of femtosecond laser ablation schemes by time-resolved soft x-ray reflective imaging.

Pump and probe reflective imaging using a soft x-ray laser probe was applied to the observation of the early stage of femtosecond laser ablation process on platinum. In strongly excited area, drastic and fast reflectivity drop was observed. In moderately excited area, the decay of the reflectivity is slower than that in the strongly excited area, and the reflectivity reaches its minimum at t = 160 ps.

Hard magnetic ferrite with a gigantic coercivity and high frequency millimetre wave rotation.

Magnetic ferrites such as Fe(3)O(4) and Fe(2)O(3) are extensively used in a range of applications because they are inexpensive and chemically stable. Here we show that rhodium-substituted ε-Fe(2)O(3), ε-Rh(x)Fe(2-x)O(3) nanomagnets prepared by a nanoscale chemical synthesis using mesoporous silica as a template, exhibit a huge coercive field (H(c)) of 27 kOe at room temperature. Furthermore, a crystallographically oriented sample recorded an H(c) value of 31 kOe, which is the largest value among metal-oxide-based magnets and is comparable to those of rare-earth magnets.

Observation of ultrafast Q-band fluorescence in horse heart cytochrome c in reduced and oxidized forms.

The dynamics of fluorescence from horse heart cytochrome c is investigated in reduced (ferrous) and oxidized (ferric) forms by a streak camera and an up-conversion technique under B-band excitation at 415 nm. In the reduced form, we found the Q-band emission at 550 and 600 nm originated from the S(1) state in a short time range. A very broad continuum observed from 440 to 660 nm had only shown a slow component and was assigned to impurity.

Coherent control of spin precession motion with impulsive magnetic fields of half-cycle terahertz radiation.

Coherent control of the precession motion of magnetizations in a single crystal YFeO3 with double half-cycle pulse terahertz waves was demonstrated. Quasiferromagnetic (0.299 THz) and quasiantiferromagnetic (0.

Single-shot picosecond interferometry with one-nanometer resolution for dynamical surface morphology using a soft X-ray laser.

Using highly coherent radiation at a wavelength of 13.9 nm from a Ag-plasma soft X-ray laser, we constructed a pump-and-probe interferometer based on a double Lloyd's mirror system. The spatial resolutions are evaluated with a test pattern, showing 1.

Synthesis of an electromagnetic wave absorber for high-speed wireless communication.

Millimeter waves (30-300 GHz) are starting to be used in next generation high-speed wireless communications. To avoid electromagnetic interference in this wireless communication, finding a suitable electromagnetic wave absorber in the millimeter wave range is an urgent matter. In this work, we prepared a high-performance millimeter wave absorber composed of a series of aluminum-substituted epsilon-iron oxide, epsilon-Al(x)Fe(2-x)O(3), nanomagnets (0 < or = x < or = 0.

Thermal and non-thermal photoinduced phenomena in α'-NaV₂O₅.

Transient reflectance changes induced by pulsed photo-excitation with 1.55 and 3.1 eV photons were studied in sodium vanadate, α'-NaV₂O₅.

Persistent nuclear wave packet oscillation coexistent with incoherent vibrational population at excited F centers in KI.

We investigated nuclear wave packet dynamics in the excited state of KI F centers at 10 K using time-resolved luminescence spectroscopy. Observed transient spectrum is divided into oscillatory and non-oscillatory components. The former lasts over 11 ps without appreciable damping and is attributed to the oscillation of the wave packet consisting mainly of the A(1g) mode around the center.

Real-time capturing of the nuclear wave-packet shape in self-trapped excitons.

We measured the time evolutions of the luminescence spectra in a quasi-1D halogen-bridged platinum complex [Pt(en)(2)][Pt(en)(2)Br(2)](ClO4)(4) with a 50 fs resolution up-conversion spectroscopy and succeeded in real-time visualization of the shape of the wave packet (WP) propagating on the adiabatic potential surface of a self-trapped exciton. The behavior of the WP is in excellent agreement with a calculation based on a harmonic oscillator. We have found that the damping of the WP oscillation is highly nonexponential.