[show abstract][hide abstract] ABSTRACT: In 2011, two SR sources of KEK, PF-ring and PF-AR, needed to change the operation schedule because of the unprecedented earthquake on March 11. Though the injector linac and the storage rings suffered a serious damage, temporary recovery was accomplished quickly and the trial operation started in May. The regular user operation could be resumed in October 2011. In the restoration work after the earthquake, some old vacuum components were removed from PF-ring. This work fortunately brought an effect of settling the quadrupole-mode longitudinal instability. For the top-up injection of PF-ring, the pulsed sextupole magnet has been used instead of the conventional kicker magnets since 2011. The hybrid-fill mode in place of the single-bunch mode has become available. Recently, the 10-Hz orbit switching for the tandem circularly polarized undulators has been developed for the user operation.
Journal of Physics Conference Series 03/2013; 425(4):042014.
[show abstract][hide abstract] ABSTRACT: We have demonstrated passively mode-locked operation of a GaInN bisectional laser diode in a dispersion-compensated external cavity. With negative group velocity dispersion in the external cavity, we obtained femtosecond optical pulses after spectral filtering with a bandpass filter. The pulse duration was as short as 200 fs with a time-bandwidth product of 0.41. This is the shortest pulse ever reported for a mode-locked GaInN laser diode.
[show abstract][hide abstract] ABSTRACT: We have generated picosecond optical pulses with a peak power greater
than 300 W at 1 GHz repetition at a blue-violet wavelength using a
GaInN-based master oscillator power amplifier. The optical pulses were
generated by a mode-locked laser diode incorporating the flared
waveguide structure for the increased active region volume to obtain
higher output power. The pulses were effectively amplified by the
semiconductor optical amplifier with reduced optical confinement factor
to high peak power.
[show abstract][hide abstract] ABSTRACT: We have developed a 500-kV, 10-mA photocathode DC gun for energy recovery linac (ERL) light sources. A segmented ceramic insulator with guard rings is employed to improve robustness at high voltage operation, because this structure can prevent field emission electrons from directly striking the ceramic surface. We have recently succeeded in applying 500 kV on the ceramics for eight hours without any discharge. This high voltage testing was performed with a simple configuration without NEG pumps, cathode and anode electrodes to mainly study the field emission from a tube supporting the cathode electrode. The same high voltage testing with a full configuration necessary for beam generation was carried out up to 380 kV where some increase of radiation was observed. Up-to-date status of our gun development is presented in detail.
Journal of Physics Conference Series 06/2011; 298(1):012005.
[show abstract][hide abstract] ABSTRACT: We evaluated saturation energies and absorption recovery time dependent on reverse-bias voltage for a waveguide-coupled GaInN multiquantum well saturable absorber in a bisectional laser structure. When the applied reverse-bias was increased from 5 to 20 V, the saturation energy at 405 nm monotonically increased from 5 to 14 pJ; the linear absorption coefficient at 405 nm showed the same dependence. These dependences are different from those observed in an AlGaAs multiquantum well. The absorption recovery time was shortened to 3 ps when a highly reverse-bias voltage of 20 V was applied.
[show abstract][hide abstract] ABSTRACT: We present optical pulse generation with 100 W peak power, 3 ps temporal duration, and 1 GHz repetition from a GaInN master oscillator power amplifier (MOPA). An external cavity GaInN laser diode is passively mode-locked to generate 4 W peak power optical pulses as a master oscillator, and a semiconductor optical amplifier (SOA) effectively amplified these to a high peak power of more than 100 W. Two major factors that contributed to effective amplification of optical pulses were the generation of clean optical pulses without sub-pulse components by the GaInN mode-locked laser diode and suppression of amplified spontaneous emission in the SOA. This novel high-peak-power pulse source is used to induce multi-photon absorption to create sub-micrometer recording marks in a bulk plastic recording media. The realization of an all-semiconductor pulse source is a significant breakthrough towards a practical 3D optical data storage system.
[show abstract][hide abstract] ABSTRACT: We directly generated 1.6-ps optical pulses with a peak power of 20 W at a repetition of 1 GHz using a blue-violet GaInN mode-locked laser diode incorporating a flared waveguide operating in single transverse mode. The flared waveguide enabled optical pulses to be generated with peak powers of over six times higher than those produced using a straight waveguide while preserving the pulse duration.
[show abstract][hide abstract] ABSTRACT: We have demonstrated volumetric optical recording using an
all-semiconductor picosecond laser, which generated optical pulses with
a duration of 3 ps and a maximum peak power of 100 W at a wavelength of
404 nm and a repetition frequency of 1 GHz. This pulsed laser system
efficiently induced multiphoton absorption in the recording media due to
its high peak power and high repetition rate. The recording marks were
formed as submicrometer voids inside a single thick recording layer by
multiphoton absorption. A clear readout signal was obtained from the
[show abstract][hide abstract] ABSTRACT: We have generated single-transverse-mode optical pulses with 100 W peak power and 3 ps duration at 1 GHz repetition from a blue-violet GaInN mode-locked laser diode (MLLD) and a semiconductor optical amplifier (SOA) without the use of any pulse compression. The generation of clean optical pulses without subpulse components from the MLLD and the reduction in amplified spontaneous emission in the SOA by incorporating a flare waveguide structure resulted in effective amplification of optical pulses to produce over 100 W peak power.
[show abstract][hide abstract] ABSTRACT: Passive mode locking of a bisectional GaInN quantum well laser diode was confirmed with external-cavity geometry. Optical pulses of 3 ps duration were produced by controlling the reverse-bias voltage applied to a saturable absorber section. These are the shortest optical pulses ever generated from GaN-based laser diodes.
[show abstract][hide abstract] ABSTRACT: We fabricated a triple-section self-pulsating GaN-based laser diode (SP-LD) and investigated the dependence of self-pulsating characteristics on the saturable-absorber (SA) section length to generate optical pulses with a higher peak power and shorter duration. By shortening the SA section to 30 mum and applying a reverse bias of -12 V to the SA section, the optical pulses were shortened to 15 ps and the optical peak power became as high as 10 W with a pulse repetition frequency of 1 GHz under dc operation. This is the highest peak power so far reported in an SP-LD under dc operation.
[show abstract][hide abstract] ABSTRACT: We produced clean 3-ps-duration optical pulses from a bi-sectional GaInN laser diode with an external-cavity configuration. The peak power of the optical pulses was 3 W under passive and hybrid mode-locking at a 1 GHz repetition rate.
[show abstract][hide abstract] ABSTRACT: Aiming at the future X-ray source based on the energy recovery linac (ERL), we are making aggressive R&D efforts. Our efforts include the developments of a high- brilliance photo injector, 1.3-GHz superconducting cavities, and planned construction of the Compact ERL. We report the updated status of our ERL project.
[show abstract][hide abstract] ABSTRACT: Self-pulsations of 407 nm emitting GaN-based blue-violet laser diodes with bisectional (BS) electrodes were demonstrated by applying a reverse bias (V<sub> SA </sub>) to the subelectrode of the saturable absorber (SA) section. By increasing the injected current to the main electrode of the gain section with a reverse bias of V<sub> SA </sub>=-12 V , the optical pulses shortened to 30 ps. The optical peak output power was as high as 2.4 W with a pulse width of 30 ps and a repetition frequency of 0.9 GHz. This is so far the shortest pulse width from a self-pulsating BS GaN-based laser diode achieved by applying a reverse bias to the SA section.
[show abstract][hide abstract] ABSTRACT: The KEK Linac delivers the beam to KEK Photon factory storage ring (PF), KEKB ring and the advanced ring for photon factory (PF-AR). In order to deliver the beam to the KEK-photon factory and KEKB ring simultaneously, the pulsed bending magnet was installed at the end of KEKB Linac. The pulsed bending magnet extract 2.5GeV electron beam to the PF beam transfers line. The deflection angle of the magnet is 0.114 radians and the field strength is about 1.22T. The peak current stability is better than 0.1% at 24kA operation. The maximum repetition rate is 25Hz. The 1.3m long ceramic chamber is inserted into the 1m long magnet. This system makes possible the top up operation of PF ring.
[show abstract][hide abstract] ABSTRACT: The authors observed the photoluminescence (PL) spectra of amorphous InGaZnO (a-IGZO) for the first time. At liquid nitrogen temperature, even weak near-band-edge emission was clearly observed at a wavelength of ∼400 nm (3.1 eV) accompanied by a much stronger broad deep emission peaking at around 700 nm (1.77 eV) for 1-μm-thick samples deposited by sputtering on sapphire substrates at room temperature. The PL intensity of each emission strongly depends on the electron concentration of a-IGZO ranging from 1016 to 1018 cm-3. As the carrier concentration increased, the PL intensity of the broad deep emission decreased. The near-band-edge emission energy of 3.0 eV (413 nm) was in good agreement with the estimated absorption energy of 3.03–3.08 eV (403–409 nm) at 77 K. The depth profile of the carrier concentration of the a-IGZO layer was estimated using step-etching Hall measurements and was found to be uniform. The width of the depletion layer was determined by the film-thickness dependence of the sheet carrier concentration. If the substrate-side depletion layer is negligible, they estimated the upper limit of Vbi as ∼1.9 eV (653 nm), in the middle of the bandgap, when assuming an 11.5 value for permittivity.
Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2009; 27(3):1746-.
[show abstract][hide abstract] ABSTRACT: We have generated optical pulses at 405 nm from a single-transverse-mode GaInN blue laser diode under intensive gain-switching operation with a minimum pulse duration of less than 8 ps. The maximum optical peak power was as high as 12 W with a pulse width of 10 ps. The peak power obtained is the highest value for optical pulses ever generated from a single transverse-mode GaInN laser diode.
[show abstract][hide abstract] ABSTRACT: We investigated the local atomic arrangements around In atoms of plasma-assisted molecular beam epitaxy (MBE) grown GaInNAs films using In K-edge extended X-ray absorption fine structure (EXAFS) oscillations. The obtained radial distribution function (RDF) clearly showed two peaks coming from the first nearest In–As bond and the second nearest In–cation bond. These two atomic distances were longer than the bond lengths theoretically calculated under an assumption of random distributions of Ga and In on cation sites and N and As on anion sites, respectively. It means that there are strong In–N and In–In correlations in GaInNAs films. The strong correlations suggest the formation of the InNAs-like particles, which can cause the spacially inhomogeneous emission.
Journal of Physics and Chemistry of Solids 01/2008; 69(2):298-301. · 1.53 Impact Factor