Layer thickness dependence of the terahertz emission based on spin current in ferromagnetic heterostructures

The emission with a bandwidth of 1.5 terahertz based on the spin current in the ferromagnetic heterostructure Co/Pt is demonstrated. The spin transient launched by the NIR femtosecond laser pulse in the Co/Pt is converted into the in-plane charge current due to the inverse spin Hall effect, which gives rise to the terahertz emission towards free space. The dependence of the terahertz emission on the Pt-layer thickness is investigated. To optimize the geometry structure of the new type of emitter, we developed the theoretical model by carefully analyzing the spin transport. Our model reveals the importance to take into account the interfacial spin loss. It can be used to analyze more complex heterostructures.

Development of multichannel low-energy neutron spectrometer

A multichannel low-energy neutron spectrometer for down-scattered neutron (DSN) measurements in inertial confinement fusion (ICF) experiments has been developed. Our compact-size 256-channel lithium-glass-scintillator-based spectrometer has been implemented and tested in ICF experiments with the GEKKO XII laser. We have performed time calibration of the 256-channel analog-to-digital convertor system used for DSN measurements via X-ray pulse signals. We have clearly observed the DD-primary fusion neutron signal and have successfully studied the detector's impulse response. Our detector is soon to be implemented in future ICF experiments.

Characterizing a fast-response, low-afterglow liquid scintillator for neutron time-of-flight diagnostics in fast ignition experiments

The characteristics of oxygen-enriched liquid scintillators with very low afterglow are investigated and optimized for application to a single-hit neutron spectrometer for fast ignition experiments. It is found that 1,2,4-trimethylbenzene has better characteristics as a liquid scintillator solvent than the conventional solvent, p-xylene. In addition, a benzophenon-doped BBQ liquid scintillator is shown to demonstrate very rapid time response, and therefore has potential for further use in neutron diagnostics with fast time resolution.

The photonuclear neutron and gamma-ray backgrounds in the fast ignition experiment

In the fast-ignition scheme, very hard x-rays (hereinafter referred to as γ-rays) are generated by Bremsstrahlung radiation from fast electrons. Significant backgrounds were observed around the deuterium-deuterium fusion neutron signals in the experiment in 2010. In this paper the backgrounds were studied in detail, based on Monte Carlo simulations, and they were confirmed to be γ-rays from the target, scattered γ-rays from the experimental bay walls (γ'-rays), and neutrons generated by (γ, n) reactions in either the target vacuum chamber or the diagnostic instruments (γ-n neutrons).

Down-scattered neutron imaging detector for areal density measurement of inertial confinement fusion

A custom developed (6)Li glass scintillator (APLF80+3Pr) for down-scattered neutron diagnostics in inertial confinement fusion experiments is presented. (6)Li provides an enhanced sensitivity for down-scattered neutrons in DD fusion and its experimentally observed 5-6 ns response time fulfills the requirement for down-scattered neutron detectors. A time-of-flight detector operating in the current mode using the APLF80+3Pr was designed and its feasibility observing down-scattered neutrons was demonstrated. Furthermore, a prototype design for a down-scattered neutron imaging detector was also demonstrated. This material promises viability as a future down-scattered neutron detector for the National Ignition Facility.

Ratio of low serum zinc levels in elderly Japanese people living in the central part of Japan

OBJECTIVE

Elderly patients often have impaired taste, nausea, anorexia and delayed healing of decubitus. In many of these patients, serum zinc levels are low and they respond to zinc supplementation. To date, no epidemics of zinc deficiency have been reported in Japan. We studied the prevalence of zinc deficiency and its causative factors in a typical local town in Japan.

DESIGN

Cross-sectional study.

SETTING

Nagano Prefecture (central Japan).

SUBJECTS AND METHODS

Serum zinc levels were measured in 1009 habitants (18-96 years old) who participated in an annual mass health examination program of the City in 2003. Of all subjects, 86 with low serum zinc (<65 microg/dl) or high zinc (> or =90 microg/dl) levels were randomly selected, and a dietary survey using 24-h recalling methods for 2 consecutive days was performed in 2004. Among them, blood was collected in the morning from 50 subjects (26-94 years old).

RESULTS

The percentage of those with low serum zinc levels (2.5th percentile of Americans) was 37.9% in the elderly (> or =60 years old). The age-adjusted prevalence of low serum zinc was 21.1% in the aged population. A positive correlation was detected between zinc intake and serum zinc levels in elderly subjects (> or =60 years old).

CONCLUSIONS

The possibility of zinc deficiency in adult inhabitants in central Japan rises with age. The deficiency correlates with dietary zinc intake.

Vacuum ultraviolet spectroscopy of Ce(3+)-doped SrMgF(4) with superlattice structure

X-ray diffraction of Ce(3+)-doped SrMgF(4) (SMF:Ce) crystals shows a superlattice structure, reflecting the distribution of Ce(3+) polyhedra centres observed in optical experiments. Optical absorption bands and fluorescence bands from the Ce(3+) polyhedra centres overlap in the vacuum ultraviolet (VUV) and ultraviolet (UV) regions, respectively, so that wide pumping and tuning ranges are expected for laser operation. The SMF:Ce crystals, as well as the isomorphous BaMgF(4), are candidates for a tunable laser gain material with nonlinear properties. The optical absorption, excitation, and fluorescence bands observed in the SMF:Ce crystals at low temperatures are ascribed to five distinct fluorescent centres. Three centres have well-known Ce(3+) optical characters, for example, fluorescence with double peaks separated by 2000 cm(-1) and five resolved absorption/excitation bands. These centres are assigned to Ce(3+)-polyhedra classified by weak and strong crystal fields as a consequence of the superlattice structure. The other two fluorescence bands observed in the visible region have 1.5-2 times larger linewidths than those of the former three bands. These bands are interpreted as optical transitions from complexes consisting of Ce(3+) and one or two electrons trapped at a vacancy of the nearest neighbour F(-) ligand ions.

Terahertz radiation from a shallow incidence-angle InAs emitter in a magnetic field irradiated with femtosecond laser pulses

The optimized incidence angle and magnetic field direction geometry of an InAs terahertz radiation emitter irradiated with femtosecond laser pulses in a magnetic field is reported. The optimum geometric layout is the magnetic field direction parallel to the semiconductor surface and at an incidence angle that is slightly larger than the Brewster angle. Additionally, we also observed a center frequency shift of terahertz radiation spectrum by changing the incidence angle of the excitation laser.

Chirped-pulse amplification of ultraviolet femtosecond pulses by use of Ce(3+):LiCaAlF(6) as a broadband, solid-state gain medium

Chirped-pulse amplification in the ultraviolet region is demonstrated by use of a broadband Ce(3+): LiCaAlF(6) laser medium. A modified bow-tie-style four-pass amplifier pumped by 100-mJ, 266-nm pulses from a Q -switched Nd:YAG laser has a gain factor of 370 and delivers 6-mJ, 290-nm pulses. After dispersion compensation, the output pulses can be compressed to 115 fs.

All-Solid-State Tunable Ultraviolet Subnanosecond Laser with Direct Pumping by the Fifth Harmonic of a Nd:YAG laser

We report what we believe is the first all-solid-state tunable ultraviolet laser pumped by the fifth harmonic of a Q-switched Nd:YAG laser. Our laser based on a Ce(3+):LiLuF(4) active medium stably generates a single, satellite-free, 0.88-ns pulse under 5-ns, 10-Hz repetition rate pumping conditions. A novel tilted-incident-angle side-pumping scheme resulted in a simple laser-cavity design.

Ultraviolet short pulses from an all-solid-state Ce:LiCAF master-oscillator power-amplifier system

We have developed an all-solid-state master-oscillator-power-amplifier system employing Ce:LiCAF, a new degradation-free tunable ultraviolet laser medium pumped by the fourth harmonic of conventional 10-ns Q -switched Nd:YAG lasers. The low- Q , short-cavity Ce:LiCAF master oscillator produced a satellite-free 1-ns pulse under appropriate pumping-fluence control. 18% energy extraction with sufficient gain was achieved in a single-stage, confocal, double-pass amplifier. As a result, 289-nm, 1-ns, 14-mJ pulses were efficiently obtained from this simple laser system.

Direct and passive subnanosecond pulse-train generation from a self-injection-seeded ultraviolet solid-state laser

We propose a passive self-injection-seeding scheme for the generation of short-pulse trains from various pulsed lasers. In this scheme a single subnanosecond pulse is generated from a short-cavity seeding laser. The pulse is then returned to the same gain medium and amplified regeneratively until the gain is quenched completely. Cw operation capability or an external short-pulse seeding laser is not required for generation of short-pulse trains. Based on this simple scheme an ultraviolet subnanosecond pulse train is directly and passively generated from a solid-state laser medium (Ce(3+):LuLiF(4)) pumped by a standard 10-ns laser.

Ce(3+):LuLiF(4) as a broadband ultraviolet amplification medium

Ce(3+):LuLiF(4) is shown to have a broad gain spectrum, which is attractive for short-pulse applications. A large small-signal gain over 6 dB/cm and a sufficiently large saturation fluence of 50 mJ/cm(2) were observed for 10-ns probe pulses under KrF excimer laser pumping. In a confocal four-pass configuration, 17-dB amplification was demonstrated for 325-nm picosecond pulses, and 20-dB gain was demonstrated for cw laser light.

Terawatt KrF/Ti:sapphire hybrid laser system

A terawatt KrF/Ti:sapphire hybrid laser system with a high contrast between amplified spontaneous emission and the main pulses has been developed with an output energy of 130 mJ in 130-fs pulses. An efficient frequencytripling scheme with Ti:sapphire is demonstrated with an efficiency of 11% in the 100-fs regime with LiB(3)O(5) and beta-BaB(2)O(4).

Pulse evolution dynamics of a femtosecond passively mode-locked Ti:sapphire laser

The pulse-formation process in a femtosecond passively mode-locked Ti:sapphire laser with a saturable absorber is investigated. The time to reach the steady state is 200 micros. The formation time dependence on the dye concentration and the coincidence of the steady-state pulse width with the self-mode-locked state without a saturable absorber indicate that the function of the saturable absorber is mainly to induce the initial modulation and to shorten the pulse-formation time.

Generation of 50-fsec pulses from a pulse-compressed, cw, passively mode-locked Ti:sapphire laser

Stable pulses of less than 150 fsec are generated directly from a tunable cw passively mode-locked Ti:sapphire laser, through a balance of self-phase modulation in the Ti:sapphire rod and negative group-velocity dispersion produced by a prism pair. After external fiber compression, 50-fsec pulses are obtained at approximately 750 nm.

Multiterawatt subpicosecond KrF laser

A 390-fsec pulse with a peak power of 4 TW has been obtained in KrF, yielding an output energy of 1.5 J from an electron-beam-pumped amplifier with an active cross section of 320 cm(2). The amplified spontaneous emission is as low as 1.8% in energy. An initial pulse width of 210 fsec is increased to 390 fsec in the amplifier, mainly as a result of linear dispersion in the thick windows and lenses used throughout the system. Nonlinear absorption and self-phase modulation are not significant in the 2.5-cm-thick CaF(2) output window at an intensity of 13 GW/cm(2).

Single-shot measurement of subpicosecond KrF pulse width by three-photon fluorescence of the XeF visible transition

The intensity of the XeF C-A transition induced by a subpicosecond KrF laser is shown to have a cubic dependence on KrF laser intensity. The third-order autocorrelation technique for measuring the duration of a single KrF subpicosecond pulse has been developed utilizing this visible transition. A pulse width of 220 fsec was successfully measured with a high contrast of ~10. The visible fluorescence is more useful to researchers than vacuum-UV fluorescences. Furthermore, this simple technique may be applied over a wide UV wavelength region from 204 to 306 nm.