Noboru Nakano

Bio: Noboru Nakano is an academic researcher from University of Tokyo. The author has contributed to research in topics: Laser & Picosecond. The author has an hindex of 7, co-authored 24 publications receiving 515 citations.

Development of a flat-field grazing-incidence XUV spectrometer and its application in picosecond XUV spectroscopy.

Abstract: A new type of grazing-incidence spectrometer with a flat focal field is developed, and XUV spectroscopy in the extreme ultraviolet region ranging from 15 to 200 A is carried out. Soft x-ray line spectra emitted from picosecond laser plasmas of aluminum and iron targets are measured and good resolutions are obtained in the XUV region. The spectral regions of detection are extended to shorter wavelengths (15 A) using a finer spaced grating. Computational studies on x-ray spectra are also performed taking into account the transient characteristics of picosecond laser-produced plasmas; the importance of the transient treatment is clearly shown. This type of soft x-ray spectrometer should be useful for time-resolved picosecond soft x-ray spectroscopy.

Concentration Dependence of Fluorescence Lifetime of Nd3+-Doped Gd3Ga5O12Lasers

Abstract: The Nd3+ concentration dependence of the fluorescence lifetime in laser crystal Gd3Ga5O12(GGG) for high power and high efficiency solid state laser is reported for the first time The dominant mechanism of the concentration quenching in Nd3+: GGG rises from the electric dipole-dipole interaction between Nd3+ ions The nonradiative transition probability of the 4F3/2 state is found to be proportional to the Nd3+ concentration squared up to the Nd3+ concentration of 5×1020 cm-3 The optimum Nd3+ concentration in Nd3+: GGG is estimated to be (34±05)×1020 cm-3 in pulsed laser operation

X-ray generation from laser-produced plasmas and its atomic-number dependence

Abstract: Experimental studies of the x-ray generation from laser plasmas are performed by using a picosecond high-power laser The intensity of emitted x rays shows a periodic variation as a function of the atomic number of target materials Calculations based on the transient collisional-radiative model, rather than the conventional steady-state coronal model, are carried out Experimental and computational results show good agreement with each other, and indicate the importance of the transient nature of multiple-ionization processes The dependence of hot-electron temperature on the atomic number is briefly discussed

Energies and time-resolved spectroscopy of 10-2000-A

Abstract: Various characteristics of x-ray emission from laser plasmas produced by a picosecond YAG laser (where YAG represents yttrium aluminum garnet) are investigated in the wide wavelength band ranging from 10 to 2000 A from the point of view that emitted radiation from laser plasmas is applied to many purposes, such as laser fusion, x-ray lasers, x-ray sources, and solid-state physics. In this wide wavelength band, extremely different dependences of x-ray energies on input laser energies are made clear. With a decrease of the wavelength, the slope of the dependences increases. Decay times of emitted x-rays from laser plasmas are approximately proportional to the wavelengths. Computational studies are also performed in the framework of a transient collisional radiative model in order to explain the experimental results.

Operation of a free-electron laser from the extreme ultraviolet to the water window

Abstract: We report results on the performance of a free-electron laser operating at a wavelength of 13.7 nm where unprecedented peak and average powers for a coherent extreme-ultraviolet radiation source have been measured. In the saturation regime, the peak energy approached 170 J for individual pulses, and the average energy per pulse reached 70 J. The pulse duration was in the region of 10 fs, and peak powers of 10 GW were achieved. At a pulse repetition frequency of 700 pulses per second, the average extreme-ultraviolet power reached 20 mW. The output beam also contained a significant contribution from odd harmonics of approximately 0.6% and 0.03% for the 3rd (4.6 nm) and the 5th (2.75 nm) harmonics, respectively. At 2.75 nm the 5th harmonic of the radiation reaches deep into the water window, a wavelength range that is crucially important for the investigation of biological samples.

X-ray Thomson scattering in high energy density plasmas

Abstract: Accurate x-ray scattering techniques to measure the physical properties of dense plasmas have been developed for applications in high energy density physics. This class of experiments produces short-lived hot dense states of matter with electron densities in the range of solid density and higher where powerful penetrating x-ray sources have become available for probing. Experiments have employed laser-based x-ray sources that provide sufficient photon numbers in narrow bandwidth spectral lines, allowing spectrally resolved x-ray scattering measurements from these plasmas. The backscattering spectrum accesses the noncollective Compton scattering regime which provides accurate diagnostic information on the temperature, density, and ionization state. The forward scattering spectrum has been shown to measure the collective plasmon oscillations. Besides extracting the standard plasma parameters, density and temperature, forward scattering yields new observables such as a direct measure of collisions and quantum effects. Dense matter theory relates scattering spectra with the dielectric function and structure factors that determine the physical properties of matter. Applications to radiation-heated and shock-compressed matter have demonstrated accurate measurements of compression and heating with up to picosecond temporal resolution. The ongoing development of suitable x-ray sources and facilities will enable experiments in a wide range of research areas including inertial confinement fusion,more » radiation hydrodynamics, material science, or laboratory astrophysics.« less

High harmonic generation in the relativistic limit

Abstract: The generation of extremely bright coherent X-ray pulses in the femtosecond and attosecond regime is currently one of the most exciting frontiers of physics–allowing, for the first time, measurements with unprecedented temporal resolution1,2,3,4,5,6. Harmonics from laser–solid target interactions have been identified as a means of achieving fields as high as the Schwinger limit2,7 (E=1.3×1016 V m−1) and as a highly promising route to high-efficiency attosecond (10−18 s) pulses8 owing to their intrinsically phase-locked nature. The key steps to attain these goals are achieving high conversion efficiencies and a slow decay of harmonic efficiency to high orders by driving harmonic production to the relativistic limit1. Here we present the first experimental demonstration of high harmonic generation in the relativistic limit, obtained on the Vulcan Petawatt laser9. High conversion efficiencies (η>10−6 per harmonic) and bright emission (>1022 photons s−1 mm−2 mrad−2 (0.1% bandwidth)) are observed at wavelengths <4 nm (the `water-window' region of particular interest for bio-microscopy).

Spectroscopic, optical, and thermomechanical properties of neodymium- and chromium-doped gadolinium scandium gallium garnet

Abstract: Spectroscopic, optical, and thermomechanical properties of gadolinium scandium gallium garnet doped with trivalent neodymium and/or chromium are reported for use in the design of high-power solid-state lasers

Laser-generated ultrasound: its properties, mechanisms and multifarious applications

Abstract: The laser generation of ultrasound in solids is reviewed with particular emphasis on the application of this unique ultrasonic source. Three regimes for the generation of ultrasound in solids using lasers in the visible near infrared wavelength region exist: thermoelastic, plasma and constrained surface source regimes. The mechanism for ultrasonic generation in each of these regimes is given. Recent experimental investigations into laser-generated ultrasound are also described, including a description of a different mechanism for the generation of ultrasound in solids using a CO2 laser. Finally, the many applications of laser-generated ultrasound are reviewed. These applications range from nondestructive testing to the determination of candle flame parameters. Possible future applications are also outlined.