Y2Si2O7:Eu/SiO2 core shell phosphor particles prepared by flame spray pyrolysis

This paper reports the synthesis of core shell phosphor particles (Y₂Si₂O₇:Eu/SiO₂) produced by flame spray pyrolysis with yttrium and europium nitrates and colloidal silica dispersed precursor solutions. Particles of various structures were produced, including heterogeneous, core shell and non-spherical core shell particles, depending on the synthesis conditions; the ideal core shell structure was obtained under the highest flame temperature and high silicon concentration in the precursor solution. Based on the phase diagram, the formation of the core shell structure was caused by the separation of each component at the liquid phase in the synthesis route. In the energy-dispersive X-ray spectroscopy, yttrium could be detected only at the core part of the particle, while silicon and oxygen could be detected at both the shell and core parts. Under ultraviolet excitation, the ideal core shell particles of Y₂Si₂O₇:Eu showed photoluminescent characteristics. Consequently, it could be concluded that Y₂Si₂O₇:Eu/SiO₂ core shell phosphor particles were successfully synthesized by flame spray pyrolysis.     

Charge transport near pressure-induced antiferromagnetic quantum critical point in Magnéli-phase vanadium oxides

Resistivity (ρ) measurements on Magnéli phases V₇O₁₃ and V₈O₁₅ were performed under high pressures up to 3.5GPa. We have achieved a pressure-induced transition from an antiferromagnetic metal to a paramagnetic metal (PM) at critical pressures P_c≈3.4 and 3.3 GPa for V₇O₁₃ and V₈O₁₅, respectively. The critical behavior of ρ(T) near P_c turned out to be quite unusual in that no noticeable precursor effect was observed. This strongly contrasts with the canonical quantum critical point behavior observed in chemically modified systems such as Ni(S,Se)₂ and V₂O₃. We propose that the presence of two distinct Fermi surface segments is responsible for the observed unusual behaviors.     

Intensity and frequency noise characteristics of two coherently-added injection-locked Nd:YAG lasers

Coherent addition of two injection-locked Nd:YAG lasers has been performed. A maximum output power of 4.4 W and addition efficiency of 0.94 was achieved, which is the highest power-coupling efficiency ever reported. It was shown experimentally that the frequency and intensity noise level of the coherently-added laser are the same as those of a single injection-locked laser. In particular, no additional intensity noise was observed above the relaxation oscillation frequency of the slave laser, which is suitable for use as the light source for a future gravitational wave detector. The frequency noise of the coherently-added laser was suppressed to 1×10^-4 Hz/ by controlling that of the master laser, and the intensity noise was also suppressed to 1×10^-8 / by controlling the intensity of pump lasers used for the slave lasers. Received: 11 April 2001 / Revised version: 20 June 2001 / Published online: 19 September 2001     

Unusual behavior of nuclear relaxation in CeCu2Si2 “possible evidence for triplet superconductivity”

Nuclear relaxation of ⁶³Cu in the superconducting state of the Kondo-lattice system CeCu₂Si₂ has been studied with the use of the ⁶³Cu nuclear quadrupole resonance technique under zero field and down to 65mK. The nuclear spin-lattice relaxation rate (1/T₁) decreases drastically just below T_c=0.67 K down to 0.5T_c without the apparent enchanced behavior and then is found to be almost temperature independent below 0.3T_c. These results suggest that the superconductivity in CeCu₂Si₂ is not in the usual BCS regime. The analysis based upon the existing triplet pairing model with an anisotropic energy gap describes well the behavior from T_c down to 0.5T_c, while the temperature independence below 0.3T_c remains unexplained.     

Wideband and high frequency stabilization of an injection-locked Nd:YAG laser to a high-finesse Fabry Perot cavity

High frequency stabilization of a 2.2-W injection-locked laser-diode-pumped Nd:YAG laser to a high-finesse optical cavity has been realized by frequency control of the master laser. With the help of an external electro-optical modulator, the feedback bandwidth was extended to 1 MHz and the frequency noise relative to the reference cavity was suppressed to 3 x 10(-4) Hz/Hz(1/2) below 1 kHz. This feedback laser system is an ideal laser source for gravitational wave detectors, which require both ultralow frequency noise and high output power.     

Supercontinuum generation using Raman fiber laser

Using a phosphosilicate-doped continuous-wave Raman fiber laser, a 350-m single-mode fiber, and a 50% feedback fiber Bragg grating at 1483.4 nm, we obtained a high-efficiency ultra-broadband (1434–1527 nm) supercontinuum (SC) centered at 1483.4 nm with an average output power of 2.1 W, a spectral intensity of 22.3 mWnm^-1, and a nonlinear conversion efficiency of 94%. Increasing the fiber length in the Raman cavity to 1840 m gave simultaneous SC centered at 1483.4 nm and 1239 nm. An average power of 2.3 W in the bandwidth of 1434–1544 nm and 0.2 W in the bandwidth of 1224–1257 nm is obtained. The temperature dependence of the SC was also investigated.PACS 42.55.Wd; 42.81.-i; 42.65.-k; 42.65.ReThis revised version was published in August 2003 with corrections to the affiliation of Mr. Taniguchi.     

Doppler effect in resonant photoemission from SF6: correlation between Doppler profile and Auger emission anisotropy

Fragmentation of the SF6 molecule upon F 1s excitation has been studied by resonant photoemission. The F atomiclike Auger line exhibits the characteristic Doppler profile that depends on the direction of the photoelectron momentum relative to the polarization vector of the radiation as well as on the photon energy. The measured Doppler profiles are analyzed by the model simulation that takes account of the anisotropy of the Auger emission in the molecular frame. The Auger anisotropy extracted from the data decreases with an increase in the F-SF5 internuclear distance.     

The second law of thermodynamics under unitary evolution and external operations

The von Neumann entropy cannot represent the thermodynamic entropy of equilibrium pure states in isolated quantum systems. The diagonal entropy, which is the Shannon entropy in the energy eigenbasis at each instant of time, is a natural generalization of the von Neumann entropy and applicable to equilibrium pure states. We show that the diagonal entropy is consistent with the second law of thermodynamics upon arbitrary external unitary operations. In terms of the diagonal entropy, thermodynamic irreversibility follows from the facts that quantum trajectories under unitary evolution are restricted by the Hamiltonian dynamics and that the external operation is performed without reference to the microscopic state of the system.     

Sequence of phase transitions in a quasi-one-dimensional β-Na<Subscript>0.33</Subscript>V<Subscript>2</Subscript>O<Subscript>5</Subscript> compound with variable valence

The thermal properties—specific heat, thermal conductivity, and thermal expansion coefficients—of a single crystal of quasi-one-dimensional variable-valence β-Na_0.33V₂O₅ compound were studied. With lowering temperature, it sequentially undergoes the structural (T _S ～ 230 K), charge (T _C ～ 136 K), and magnetic (T _N ～ 22 K) phase transitions. The structural transition at T _S , resulting in the ordering of the Na ions, and the charge ordering at T _C , resulting in the charge redistribution over the positions of V ions, are accompanied by the anomalies in the temperature dependences of all the studied properties. The magnetic ordering at T _N results in the appearance of the canted antiferromagnetic structure and manifests itself only in the anomaly in the temperature dependences of the thermal expansion coefficients.     

Measurements of Rayleigh–Taylor instability growth of laser-shocked iron–silicon alloy

The Rayleigh–Taylor (RT) instability of liquid iron alloys is important for understanding the core formation mechanism in the Earth. Here we first report the measurement of RT instability growth for a liquid iron–silicon (Fe–Si) alloy, which is one of the major candidate for the material of the Earth’s core, using a high power laser. We optimized the measurement setup and analytical technique to observe the growth of perturbation on an Fe–Si sample surface. The growth of perturbation amplitude on the Fe–Si alloy under high pressure and temperature was successfully observed using in situ X-ray radiography. The growth rate of the RT instability for the Fe–Si alloy on about 1000?GPa was estimated to be 0.3 ns^?1.