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HEYA Manabu

    Department of Electronic Engineering and Computer Science　Professor
Last Updated :2024/05/19

Researcher Information

Degree

  • Ph.D.（Osaka University）

Research funding number

  • 40324818

J-Global ID

Published Papers

  • Yang Zhang; Takumi Besshi; Miho Tsuyama; Manabu Heya; Hitoshi Nakano
    Journal of Laser Applications Laser Institute of America 35 (1) 012014 - 012014 1042-346X 2023/01 [Refereed]
     
    Laser peening is a promising surface treatment technique for enhancing the mechanical performance of metals. In laser peening, the plasma confinement layer contributes to the generation of high-pressure shockwaves by suppressing the expansion of laser-induced plasma. Therefore, the choice of a plasma confinement layer is important for improving laser peening effectiveness. For laser peening in environments where liquid materials cannot be used as a plasma confinement layer, alginate gel, which is a pliable material with shape-following capabilities, has been proposed to reduce the acoustic impedance mismatch caused by surface roughness when using solid materials. In this study, the feasibility of alginate gel as a plasma confinement layer and an appropriate process window for laser irradiation were investigated. The results of this study are then presented.
  • Keisuke Takenaka; Yuji Sato; Norio Yoshida; Mitunari Yoshitani; Manabu Heya; Masahiro Tsukamoto
    Journal of Laser Applications 34 42041  2022/11 [Refereed]
     
    The authors developed a galvano selective laser melting (SLM) system equipped with a blue diode laser and clarified that the volume of the fabricated pure copper part has an influence on the relative density. SLM is a 3D printing technology. Blue diode laser is anticipated to effectively form pure copper parts because the absorptance of 450 nm light on pure copper is higher than that of conventional 1 μm light. In our previous study, the authors reported a newly developed blue diode laser whose wavelength was 450 nm. Laser power and fiber core diameter were 200 W and 100 μm, respectively. In this study, the height and width of the copper part were changed, and their influence on the density of the parts was investigated. As a result, it was found that the larger the volume of the fabricated copper part, the lower the density. In addition, the diluted layer of pure copper and the stainless steel baseplate in the copper part were measured. By controlling the amount of laser heat input between the diluted layer and the undiluted layer, it was possible to form a pure copper part with a high density of 99.6%.
  • Copper Alloy Layer Formation with Multi Beam Type Laser Coating with Blue Diode Lasers
    佐藤雄二; 森本雄喜; 小野和宏; 竹中啓輔; 鎌田恒好; 部谷学; 塚本雅裕
    電気学会論文誌C 142 (10) 1075 - 1080 2022/10 [Refereed]
     
    A copper has been widely applied for various industrial components such as heat exchangers, heat pipes, electro circuits and motors because of having excellent properties such as thermal conductivity and electrical conductivity. Besides the copper is expected to be used for handrails, doorknobs etc., which touched by many people to prevent from infectious diseases because of having the excellent properties such as an antibacterial property and a virus inactivation property. However, copper is low strength to only about 40% as strong as stainless steel. To add a new function of virus inactivation property to the surface keeping the strength, it is necessary to develop a coating technology to form a copper layer on the surface. Thus, we have developed a multi beam type laser metal deposition method with a high intensity blue diode laser which newly developed with an output power of 200W. As a result, Cu-Zn alloy layer was formed on the stainless-steel plate with no pores at the output power of 30W and scanning speed of 6mm/s.
  • Investigation of Determination of Laser Welding Conditions for Prediction of Penetration Depths Using Hablanian Plot
    部谷学; 舟山博人; 小澤健治
    電気学会論文誌C 142 (10) 1068 - 1074 2022/10 [Refereed]
     
    In order to establish a method to precisely predict penetration depths for macro and micro laser welding at manufacturing sites, we have investigated how to determine experimental conditions for Hablanian plot. We need to obtain three approximate curves (standard approximate curve, error approximate curve, and coefficient approximate curve) for an accurate prediction of penetration depths. We have discussed how to obtain three approximate curves using laser welding data by the use of the fiber laser. As a result, the following findings could be derived. (1) Cubic polynomial is probable as one of the candidates of a function for three approximate curves. (2) A focusing lens used and a spot diameter should be first determined. Second, laser welding experiments should be carried out with changing Log10(Vd/K) and P at regular intervals. (3) Prediction errors can be respectively reduced down to ~0.06 and ~0.03 for macro and micro welding above a penetration depth of 4 mm and 0.4 mm.
  • A Fujinaga; S Umeda; M Heya; H Ogata; N Kishimoto
    Journal of Water and Environment Technology Japan Society on Water Environment 20 (1) 1 - 10 2022/02 [Refereed]
     
    Microbial fuel cells (MFCs) can generate electricity from organic compounds present in wastewater; however, the resulting small electric power is insufficient for practical applications. This issue occurs because of the high internal resistance of MFCs, which can be addressed by first precisely measuring these internal resistances. However, a standard method for measuring the internal resistance, which depends on the conditions of the MFCs, does not exist. Therefore, five measurement methods in the open-circuit (OC) mode were evaluated in this study. In addition, the internal resistances in the closed-circuit (CC) mode were measured using a one-resistance method and electrochemical impedance spectroscopy (EIS). The values obtained by the linear sweep intensity of current potentiometry (LSIP) method were different from those measured by the other four methods. This was presumably because LSIP involved forcibly flowing electric current in the MFCs. The one-resistance method yielded similar internal resistances to those of the other methods in the OC mode. In addition, this method was applicable in the CC mode. Therefore, the one-resistance method can be used during discharging and for developing MFCs based on discharging.
  • Effects of laser peening parameters on plastic deformation in aqueous glycerol solution as plasma confinement layer
    N S Masroon; H Hirata; M Tsuyama; M Heya; H Nakano
    JLMN-Journal of Laser Micro/Nanoengineering 16 (3) 160 - 165 2021/12 [Refereed]
     
    Laser peening is a surface treatment technique that can improve the properties of metallic materials. Installation of the plasma confinement layer with liquid plays an important role to obtain high magnitude shock wave pressure. In this study, the effects of laser peening parameters in glycerol solution as plasma confinement layer were investigated through hardness and residual stress measurements. The stainless steel, SUS316L, has been used as a target sample. The experiments were carried out by varying the concentration of glycerol solution. Laser peening treatment under a liquid confining medium is advantageous because a dual-impulse peening effect can be obtained by the shock wave pressure due to the confinement of laser-induced plasma and collapse of the laser-induced cavitation bubble. The impact from both shock wave pressures and dynamics of a laser-induced cavitation bubble have been evaluated to consider deeply the effects of laser peening parameters on the hardness and residual stress of laser-peened samples. Glycerol solution around 20 wt% in concentration was found to be desirable in any laser peening parameters to achieve efficient laser peening treatment.
  • Laser peening with solid-state medium having high acoustic impedance as plasma confinement layer
    M Tsuyama; Y Sugimoto; M Heya; H Nakano
    JLMN-Journal of Laser Micro/Nanoengineering 16 (3) 173 - 177 2021/12 [Refereed]
     
    In laser peening, a high amplitude shock impulse is necessary. The shock impulse can be increased by confinement of the laser-produced plasma through the acoustic impedance of a plasma confinement layer. In this study, a solid-state medium having high acoustic impedance was used as the plasma confinement layer for laser peening. It was found that elimination of the acoustic impedance mismatch is important for efficient laser peening. By injecting silicone oil into the gap between the solid-state medium and the target sample, the influence of impedance mismatch was reduced and efficient laser peening was achieved. Greater values of hardness and compressive residual stress were obtained in comparison with water used as the plasma confinement layer.
  • Control of plasma confinement layer for effective laser-peening
    Y Zhang; N S Masroon; Y Namba; M Tsuyama; M Heya; H Nakano
    JLMN-Journal of Laser Micro/Nanoengineering 16 (2) 80 - 83 2021/10 [Refereed]
     
    Laser peening is a promising technique for cold working a metal sample by laser-induced shock waves. The amplitude of the shock waves can be increased by a plasma confinement layer, which suppresses the expansion of the laser-produced plasma. The properties of the plasma confinement layer affect the results of the laser peening treatment. In this study, an aqueous sucrose solution, which has a higher acoustic impedance than water, was selected as the plasma confinement layer. The concentration and temperature were varied to control the acoustic impedance and viscosity of the sucrose solution. It was found that when the concentration was around 20 wt% at a temperature of 60℃, effective laser peening could be achieved.
  • Investigation of Laser Micro Welding Data for Stainless Steel Using Hablanian Plot
    部谷学; 舟山博人; 小澤健治
    電気学会論文誌C 141 (7) 776 - 781 2021/07 [Refereed]
     
    We have analyzed the laser micro welding data for stainless steel (SUS304) by using the Hablanian plot. We have determined the standard fitting curve, which is obtained by fitting the laser micro welding data with a cubic polynomial, and the fitting difference (ΔLog10(Vd/K)) in Log10(Vd/K) between the standard fitting curve and the corresponding experimental data. When ΔLog10(Vd/K) is equal to 0, we can precisely predict penetration depths by using the standard fitting curve. We have investigated the dependences of ΔLog10(Vd/K) on penetration depth, welding speed, laser power, and spot diameter. The following findings could be derived. (1) The standard fitting curve for micro welding was mostly corresponding to that for macro welding. (2) ΔLog10(Vd/K) had negative values above penetration depth of ~0.7-0.8 mm. The deeper penetration depth became, the more markedly ΔLog10(Vd/K) decreased. (3) It is essential for accurate prediction of penetration depth to collect welding data for each spot diameter and to obtain the fitting difference ΔLog10(Vd/K) for each spot diameter. (4) We showed that prediction of penetration depth with correction using ΔLog10(Vd/K) data for each spot size is available.
  • M Heya; H Furukawa; M Tsuyama; H Nakano
    Journal of Applied Physics AIP Publishing 129 (23) 235108  0021-8979 2021/06 [Refereed]
     
    We have developed a one-dimensional simulation code for laser shock processing with an atomic model code, an equation of state code, and a laser ablation peening code, in order to calculate laser-plume interactions during laser shock processing. We calculated the temporal changes of some energy ratios [e.g., the ratio (α') of the thermal energy of a plume to an incident laser energy] and physical quantities, such as electron temperature, ion temperature, absorbed laser power density, and plume pressure under various laser parameters at the laser wavelengths of 355, 532, and 1064 nm. In the case of shorter pulse durations less than 10 ns, a peak plume pressure can be predicted by using α' of ∼0.25 for 1064 nm and ∼0.40 for 355 and 532 nm below the power density threshold, at which plume pressures start to saturate. These values of α' were consistent with those obtained in the previous experiments. In the case of longer pulse durations more than 10 ns, α' for 1064 nm increased up to ∼0.45 at 15 GW/cm2 and an enhanced plume pressure would generate due to plasma absorption via inverse bremsstrahlung absorption in the partially ionized region far from the initial surface of the metal and due to heat conduction of the thermal energy of the plume near the initial surface of the metal. Thus, we showed the validity of our one-dimensional simulation code for laser shock processing and will investigate laser-plume interactions using double pulses during laser shock processing in the future.
  • Water temperature as acoustic impedance control for efficient laser peening
    Noor Shahira Masroon; A Hata; M Tsuyama; M Heya; H Nakano
    International Journal for Light and Electron Optics 242 167097  2021/06 [Refereed]
     
    Laser peening is a shock processing technology that shows great potential for enhancing the surface properties of metals. In the process of laser peening, a high-pressure shock wave can be obtained by covering the metal surface with a transparent overlay, which induces plasma confinement. The plasma confinement layer suppresses the expansion of laser-produced plasma to increase the shock wave pressure amplitude. The acoustic impedance of the plasma confinement layer is an influential factor for effective laser peening. In this study, to investigate the effect of controlling the acoustic impedance of water on laser peening, experiments were carried out by varying the water temperature. The results showed that in laser peening experiments, warm water with a temperature around 60 °C could significantly improve the mechanical performance of stainless steel, suggesting that a simple method has been developed for efficient laser peening.
  • Effects of Laser Peening on Various Aluminum Alloys
    吉池勝大; 岡遼太郎; 豊藏森; Noor Shahira Masroon; 部谷学; 津山美穂; 中野人志
    レーザー研究 49 (1) 50 - 55 2021/01 [Refereed]
     
    We investigated the effects of laser peening on various aluminum alloys which are usually used for various industrial fields to estimate desirable laser parameters. Seven typical aluminum alloys were used as samples: 1050, 2017, 3003, 4032, 5052, 6061, and 7075. The laser intensity and coverage, which is the number of laser pulses irradiated per unit, were varied during our laser peening experiments. We found that the surface hardness due to the work hardening and the compressive residual stress depend mainly on the coverage in aluminum alloys. A laser intensity around 1.0 GW/cm2 with coverage around 2,000% is desirable for the efficient laser peening of aluminum alloys.
  • Effect of specific surface area on syngas production of pure ceria in high-temperature thermochemical redox cycling coupled to methane partial oxidation
    M Heya; X Gao; A Tricoli; W Lipiński
    RSC Advances 10 36617 - 36626 2020/10 [Refereed]
     
    Specific surface area is a key parameter determining the rates of thermochemical redox reactions in metal oxides. We have experimentally investigated the effect of specific surface area on syngas production of pure ceria powders under two experiments such as a heating experiment without syngas production and an isothermal thermochemical redox cycling experiment using carbon dioxide splitting and methane partial oxidation. The specific surface area of ceria powders decreased relatively slowly during 50 hours of ceria powder heating without syngas production due to a combination of oriented attachment and grain-boundary diffusion. When cycled thermochemically, the specific surface area of ceria powders rapidly decreased only in the initial 10 minutes of reduction in the 1st cycle due to evaporation and condensation. A significant decrease of specific surface area during the initial stage of thermochemical ceria powder cycling is unavoidable even if temperatures as low as T = 1173 K are used in the reduction reaction coupled to methane partial oxidation.
  • Prediction of Penetration Depth by Laser Welding Using Hablanian Plot Method and Linear Multiple Regression Analysis
    部谷学; 舟山博人; 坪井昭彦; 田川正雄
    電気学会論文誌C 140 (7) 675 - 681 2020/07 [Refereed]
     
    In order to prove the validity of prediction of penetration depth using Hablanian plot, we have compared experimentally-obtained penetration depths with those predicted by Hablanian plot and linear multiple regression analysis. The experimental results with ~1200 data points were obtained from bead-on-plate welding tests by the laser job shop. Stainless steel plates and four types of industrial CW lasers were used in these tests. From linear multiple regression analysis, it was found that dominating factors were laser power, welding speed, and spot diameter. On the other hand, we can predict the penetration depth using the 3th-degree polynomial fitting curve (standard curve) expressed by Hablanian plot with two dimensionless parameters. The fitting difference between the standard curve and a data point results in the error of prediction. From Hablanian plot, it showed (1) that this fitting difference was dependent on some factors (such as laser power, welding speed, power density, and penetration depth), (2) that the fitting difference was, respectively, negative and positive in the lower and middle welding speed ranges, and (3) that the penetration depth could be precisely predicted by correcting the fitting difference in welding speed from the standard curve compared to the results predicted by linear multiple regression analysis.
  • Prediction of Penetration Depths with CW Fiber Lasers of 0.01-10 kW Using Hablanian Plot
    部谷学; 舟山博人; 坪井昭彦; 田川正雄
    レーザ加工学会誌 26 (3) 202 - 206 2019/10 [Refereed]
     
    In order to prove the validity of prediction of penetration depths using Hablanian plot, experimentally-obtained penetration depths with CW fiber lasers of 0.01～10 kW were compared with those predicted by Hablanian plot. The experimental results with ～900 data points for stainless steel plates were obtained from bead-on-plate welding tests performed in the laser job shop. Laser power, welding speed and spot diameter were varied as laser conditions. The experimental results expressed by Hablanian plot with two dimensionless parameters（Log10（Vd/K）and Log10（P（/ θtk）））were fitted by the 3th-degree polynomial fitting curve（standard fitting curve）. The fitting difference（ΔLog10（P/ θtk））between the standard fitting curve and thecorresponding experimental result was larger at deeper penetration depths, and resulted in the error of prediction. This fitting difference at a given Log10（Vd/K）was calculated and obtained as a function of laser power. The error of prediction after correction for fitting difference was lower than that before correction. Thus, we showed that correction for fitting difference was essential for accurate prediction of penetration depth using Hablanian plot.
  • Model-based evaluation of the effect of discharge-charge on electric power generation of microbial fuel cells
    A Fujinaga; S Taniguchi; R Takanami; H Ozaki; T Tamatani; M Heya; N Kishimoto
    Journal of Water and Environment Technology 17 (2) 100 - 108 2019/04 [Refereed]
     
    As a method for raising the electric power of microbial fuel cells (MFC), we have noticed that repeat of discharge (closed circuit: CC) and charge (open circuit: OC) produces higher electric power than continuous CC. We tried to find the best interval time for the electric power generation of MFC using compost by experiments and model simulations. As a result of the experiment, the interval time of CC and OC, which was less than 60 seconds, produced about 1.2 times-higher electric power output than the continuous CC. In addition, as for the fixed interval time of CC, which was 30 s, the longer time of OC produced higher power. It is difficult to keep the same condition on the MFC, because each experiment uses the power of the MFC, and then the voltage decreases. Therefore, we simulated the experiments by making a mathematical model for estimating the electric power. The model was based on variation of the concentration of organic compounds, which are consumed by electric current and supplied by diffusion. As a result of the calculation, the effective interval time of CC and OC is less than 15 s. As for the fixed time of CC, the model shows the longer time of OC generates the higher power; however, as the time efficiency, the shorter time of OC is preferable. Therefore, the time efficiency should be considered for practical use of the MFC.
  • Effect of laser peening with glycerol as plasma confinement layer
    M Tsuyama; N Ehara; K Yamashita; M Heya; H Nakano
    Applied Physics A Springer 124 (250) 1 - 4 2018/01 [Refereed]
     
    The effects of controlling the plasma confinement layer on laser peening were investigated by measuring the hardness and residual stress of laser-peened stainless steels. The plasma confinement layer contributes to increasing the pressure of shock waves by suppressing the expansion of the laser-produced plasma. Most previous studies on laser peening have employed water as the plasma confinement layer. In this study, a glycerol solution is used in the context of a large acoustic impedance. It is found that this glycerol solution is superior to water in its ability to confine plasma and that suitable conditions exist for the glycerol solution to act as a plasma confinement layer to achieve efficient laser peening.
  • 津山美穂; 榎原直哉; 山下数馬; 部谷学; 中野人志
    レーザー研究 レーザー学会 45 (10) 658 - 661 0387-0200 2017/10 [Refereed]
     
    Laser peening, which is a surface treatment technique that improves the mechanical performance of metals, is produced by plastic deformation due to laser-induced shock waves. Current studies on laser peening focus on the magnitude of compressive residual stress and the hardness of the laser-peened material. Systematic studies are required that consider many parameters related to efficient laser peening. In this study, we investigated effect of controlling the plasma confinement layer on laser peening and used an aqueous sucrose solution as the plasma confinement layer. The results indicate that the aqueous sucrose solution has the potential to confine laser-induced plasma. We improved the laser peening effect with an aqueous sucrose solution as the plasma confinement layer more than using water.
  • 飯田裕之; 王明炎; 古河裕之; 津山美穂; 草場光博; 中野人志; 部谷学
    レーザ加工学会誌 レーザ加工学会 24 (2) 110 - 116 1881-6797 2017/06 [Refereed]
     
    In order to produce compressive residual stress on a metallic sample, the following three experiments of Ink-LP (Laser peening) processing have been conducted using a black liquid ink as an absorber: (Exp-1) a single shot experiment using a glass slide as a confinement layer to investigate probable conditions of Ink-LP processing; (Exp-2) a single shot experiment to confirm the usefulness of an acrylic plate as the confinement layer; and (Exp-3) an experiment using the acrylic plate by repetitive laser irradiation to confirm the generation of compressive residual stress. The samples used were A2017 aluminum alloy in (Exp-1) and (Exp-2) and SUS304 stainless steel in (Exp-3). The following findings could be derived from experimental results. (1) The depth of the dent for Ink-LP processing using the glass slide was almost the same with that of conventional LP (C-LP) processing below a power density of about 10 GW/cm2. (2) The depth of the dent for Ink-LP processing even using the acrylic plate was almost the same with those of C-LP processing using the glass slide and the acrylic plate, which indicating that Ink-LP processing using the acrylic plate would produce similar LP effects for C-LP processing. (3) Compressive residual stress within the range of about -200 to -400 MPa was observed even though when the coverage of the Ink-LP processing was only 100%.
  • 部谷学; 坪井昭彦; 田川正雄
    電気学会論文誌A The Institute of Electrical Engineers of Japan 137 (5) 271 - 277 0385-4205 2017/05 [Refereed]
     
    We analyzed the Hablanian plot results of the welding data using only fiber lasers for stainless steel (SUS304). These data were a part of those in our previous article. We discussed the following: (1) two types of unique behavior confirmed in our previous article, (2) a difference between Hablanian plot and Swift's model, and (3) the prediction of a penetration depth using Hablanian plot with pulsed lasers. The following findings could be derived. (1) Micro welding results located above the standard fitting curve for welding data using CW fiber lasers. This would result from the use of long-focus lenses. (2) The fitting curve for ff = ∼300 mm was the closest to the standard fitting curve. (3) In the higher Vd/K and P/(θtk) regions, the experimentally obtained penetration depth was ∼20% of that without any losses of a laser energy. (4) In order to predict a penetration depth using pulsed lasers, we need to obtain the Hablanian-plotted fitting curves with the corresponding duty ratios.
  • 王明炎; 長村 翔太; 飯田裕之; 金子宏; 草場光博; 部谷学
    電気学会論文誌A The Institute of Electrical Engineers of Japan 137 (5) 246 - 252 0385-4205 2017/05 [Refereed]
     
    In order to investigate the effect of surface roughening due to laser irradiation in two-step thermochemical water-splitting with CeO2 system, we irradiated reactive ceramics of CeO2-NiO system and formed groove-like structures on the surface of these samples using the two types of lasers, such as a CW laser ( = 1070 nm) and a nanosecond (Ns) pulsed-laser ( = 532 nm). We observed structural and characteristic changes after laser irradiation and thermochemical cycling, and estimated the amount of the syngas (H2 and O2 gases) during thermochemical cycling. The following findings can be derived from the experimental results. (1) The surface of the samples irradiated by a CW laser became much smoother and its color changed from milky white to blue, while the sample surface after Ns pulsed-laser irradiation was almost the same as that before laser irradiation. (2) Glass-like material was observed on the surface of the sample after thermochemical cycling, and groove-like structures partly changed into melted-like structures. (3) The amount of the syngas from the all of the irradiated samples was markedly higher than that from the unirradiated samples only at the early stage of thermochemical cycling. This reduction after a few cycles would result from the sintering of CeO2 samples under high temperature and from the separation of inorganic adhesive used as a binder. (4) Even though with lower surface area, the samples by Ns pulsed-laser irradiation emitted more syngas than those of other samples, because they have no a melted-like and smooth surface.
  • Reduction of Static Friction Coefficient of Carbon Steel (S45C) by Irradiation of Nanosecond Pulsed-laser
    部谷学; 武田信秀; 内山文宏; 沖原伸一朗; 坪井昭彦
    レーザ加工学会誌 23 (2) 59 - 67 2016/06 [Refereed]
     
    In order to experimentally investigate the reduction of static friction coefficient of carbon steel (S45C), we have irradiated carbon steel samples using a nanosecond pulsed solid state laser. We varied the laser conditions (power density and beam scanning speed) and the initial surface roughness of the samples used (0.5 – 6 m in Ra). The reduction of Ra，Rpk，Rvk，s，k were mainly confirmed within the ranges of a spot diameter of below 88 m and a beam scanning speed of below 2.0 m/s, leading to smooth surface after laser irradiation. From spatial fre-quency analysis, we speculated that spatial frequency compositions for 60 – 200 mm-1 decreased due to surface melting, resulting in the reduction of static friction coefficient after laser irradiation. Laser processing involved these findings is expected to be applied into the polishing process of the sliding surface of machine tools and the substitute of hand finishing process of molds by skilled workers.
  • 飯田裕之; 丹羽勝之; 王明炎; 古河裕之; 津山美穂; 中野人志; 草場光博; 部谷学
    電気学会論文誌A The Institute of Electrical Engineers of Japan 135 (10) 581 - 586 0385-4205 2015/10 [Refereed]
     
    In a conventional laser peening (C-LP) without a protective coating, a treated metallic surface is always melted after the C-LP processing, resulting in the generation of tensile residual stress. In order to establish a new LP technique without surface melting, we have investigated the effect of an LP (Ink-LP) using a black liquid ink (an indian ink) as an absorber. The laser wavelength and pulse duration of the laser used were 532 nm and ∼5 ns, respectively. We changed the pulse energy and spot diameter of the laser beam, resulting in the corresponding power density of ∼1 - 15 GW/cm2. The pulse number was 1. The metal sample used was an aluminum alloy (A2017). As a reference, we have conducted similar experiments for the C-LP processing, which in the metallic surface are directly irradiated, and have compared surface deformation and surface melting between the Ink-LP and C-LP processing. As a result, it was found that the Ink-LP processing can provide us with a promising LP effect with a wider treatment area and no surface melting in comparison with those of the C-LP processing. Thus, we have showed the usefulness of the Ink-LP processing using a black ink.
  • Prediction of Penetration Depth Using Hablanian Plot Based on Laser Welding Results for Stainless Steel
    部谷学; 坪井昭彦; 社本英泰; 田川正雄
    レーザ加工学会誌 21 (3) 21 - 27 2014/10 [Refereed]
     
    In order to experimentally investigate the prediction accuracy of a penetration depth, we have organized nu-merous welding results of stainless steels (SUS304) using Hablanian plot. The lasers used were three fiber lasers, one disk laser, four YAG lasers, and one laser diode. These welding data obtained from bead-on-plate welding tests by the laser job shop consisted of about 1700 data points. The following results were derived from the observa-tions: (1) Hablanian plot results could be fitted using 3th-degree polynomial fitting but not linear fitting. (2) In the lower range of two dimensionless parameters, the effect of heat conduction into the adjacent material became re-markable. (3) Welding properties expressed by Hablanian plot showed similar properties even under the different welding conditions (such as the type of laser oscillator, welding speed, and power density), except for the focal length of focusing lenses used. Hablanian plot results for the different focal lengths could be expressed by the corresponding 3th-degree polynomial fitting curves. (4) A penetration depth could be precisely calculated by using the 3th-degree polynomial fitting curve in comparison with the linear fitting curve.
  • 古河裕之; 部谷学; 中野人志
    レーザー研究 レーザー学会 42 (10) 784 - 791 0387-0200 2014/10 [Refereed]
     
    We developed an Integrated Simulation code for Laser Ablation Peening (ISLAP) to estimate the plume pressures produced by laser ablation in a water confinement regime, and to calculate the stress and strain formations in solid metals. Since controlling laser-ablation-produced-plumes is essential in laser peening, laser ablation phenomena must be studied in a water confinement regime by computer simulations. In ISLAP, the phase transitions from solid to liquid and from liquid to gas are modeled by the improved Anisimov formula. We evaluated the formation of stress and strain in solid metals by solving hydrodynamics equations, the strain-displacement relation, and the stress-strain relation. The input physical parameters are the laser peak intensity, the laser pulse duration, the laser wavelength, the temporal pulse shape, the material type, and the type of confinement material (vacuum, air, water, or glass). Using ISLAP, we can estimate the pressures of the plumes, the stress and the strain in solid metals, the plume lengths, and the ratio between the thermal energy and the internal energy of the plumes.
  • 水田 浩平; 津山美穂; 部谷学; 塚本雅裕; 柴柳敏哉; 中野人志
    レーザー研究 レーザー学会 41 (11) 942 - 945 0387-0200 2013/11 [Refereed]
     
    We investigated the effects of laser incident angle variation on the hardening of metal in laser peening experiments. We used full annealed SUS316L stainless steels as test samples. A 2nd harmonic of Nd:YAG laser light was used to produce laser-peened samples. We used Vickers microhardness tests to estimate the work hardening due to the plastic deformation caused by laser peening. The hardness of the laser-peened samples varied with the numerical aperture of the optics corresponding to the angle of incidence of the laser radiation. The hardness measurements revealed the desirable numerical aperture for laser peening experiments.
  • 高塚信行; 部谷学; 沖原伸一朗; 鈴木重啓; 北原正
    レーザ加工学会誌 レーザ加工学会 19 (3) 200 - 205 1881-6797 2012/10 [Refereed]
  • [解説論文]歯科におけるレーザー研究に重要な基礎知識
    部谷学
    レーザー歯学会誌 22 (1) 2 - 9 2011/04 [Refereed]
     
    歯科現場あるいは実験室において、レーザー歯科医療技術の発展・普及のために、多くの医師・研究者が医療応用研究に取り組んでいる。これらの研究成果を体系的に理解するためには、研究成果の正しい比較が重要であり、実験結果を第三者が再現できるよう整理することが必要となる。本解説は、レーザーの医療応用の研究に初めて携わる歯学系あるいは医学系の研究者を主たる対象とし、レーザーの基礎知識（発振原理、装置、レーザー条件、生体相互作用）について述べ、レーザー加工（治療）の実験結果を整理する上でのポイントについて概説する。（部谷学、25巻、323-331頁）
  • レーザピーニング作用に及ぼすパルス幅の影響 ―サブナノ秒レーザピーニングの優位性―
    松本康太郎; 辻俊哉; 小林祐次; 部谷学; 沖原伸一朗
    レーザ加工学会誌 17 44 - 50 2010/10 [Refereed]
     
    高効率且つ非熱的処理が期待できるサブナノ秒レーザと現状多く利用されているナノ秒レーザを用いてレーザピーニング処理を行い、パルス幅の違いがピーニング作用に与える影響を比較した。その結果、短パルス化により、供試材の表面粗さや変形量を抑え、効果的な残留応力付与（表面圧縮残留応力値と最大圧縮残留応力値と付与深度の増大）を確認することができた。これらは疲労強度の向上に繋がる可能性がある。このように、サブナノ秒レーザピーニングの優位性とマイクロマシン産業への応用の可能性を示した。（松本康太郎、辻俊哉、小林祐次、部谷学、沖原伸一朗、17巻、44-50頁）本人はレーザー加工の技術開発を指導または担当した。
  • レーザー受託加工の経営的特徴と顧客価値連鎖
    後藤俊夫; 刀原寛孝; 部谷学; 瀧口義浩
    実践経営学会 47 47 - 56 2010/08 [Refereed]
     
    レーザー受託加工業の起業実践から明らかとなった、経営的特徴と顧客価値連鎖に関する新知見についてまとめた。経営的特徴では、先端加工であるレーザー加工を受託加工する場合、市場規模や方向性が間接的に把握できることが明らかとなった。また、顧客価値連鎖では、受託加工内容によって、直接の顧客の顧客のニーズがある程度把握できることが明らかとなった。このように、レーザー受託加工業は、将来のものづくりの動向を見通せる業態であり、その継続的な経営のためには絶え間ない技術開発が重要であることが分かった。（後藤俊夫、刀原寛孝、部谷学、瀧口義浩、47巻、47-56頁）本人はレーザー加工の技術開発を指導または担当した。
  • M Heya; S Sano; H Kumasaki; Y Hashishin; K Sunada; K Yoshikawa; M Inou; H Horiike
    Jpn. J. Appl. Phys. JAPAN SOCIETY APPLIED PHYSICS 47 (11) 8622 - 8630 0021-4922 2008/11 [Refereed]
     
    The purpose of this study was to compare the acid resistance of root dentin treated with a free electron laser emitting at between lambda = 9.0 and 9.7 mu m, corresponding to the absorption peaks due to the phosphate ions. In order to obtain the optimum irradiation time for effective surface modification in the acid resistance test, we measured the temporal behaviors of acoustic wave emission and temperature rise. Lased and unlased samples were immersed in 0.1 M lactic acid, and the amount of Ca dissolved in the solution was determined after immersion times of 1-22 h. The acid resistances for lambda = 9.0 and 9.7 mu m increased only until similar to 3h. We conclude that the surface modification of root dentin leads to improved acid resistance, but that this only persists for a few hours. Subsurface modification but not surface modification would be effective in the treatment of root surface caries. [DOI: 10.1143/JJAP.47.8622]
  • M Heya; Y Iwamoto; Y Hashishin; K Yoshikawa; H Horiike
    Jpn. J. Appl. Phys. JAPAN SOC APPLIED PHYSICS 46 (3A) 1208 - 1216 0021-4922 2007/03 [Refereed]
     
    It is essential for soft tissue cutting to precisely predict the effects of laser irradiation before treatment. The purpose of the present study was to investigate the dynamic absorption coefficients of wet gelatin around lambda = 6.05 mu m (tuned to the OH bending and amide-I bands) during laser irradiation. Wet gelatin was irradiated by a tunable mid-infrared free electron laser within the wavelength range of 5.6-6.7 mu m. The incident fluence was fixed at 3.6 +/- 0.3 J/cm(2). Structural changes of the irradiated gelatin were observed with an optical microscope. At lambda = 6.05 mu m, the wet gelatin was efficiently removed due to vaporization of water, and the absorption coefficient during irradiation increased slightly by 30-40% of magnitude from that before irradiation. Thus, we showed the possibility that 6.05-mu m-light can predictably remove soft tissue without unexpected effects. A laser system with lambda = 6.05 pm is expected to be a novel cutaneous laser.
  • H Monobe; H Hori; M Heya; K Awazu; Y Shimizu
    Thin Solid Films ELSEVIER SCIENCE SA 499 259 - 262 0040-6090 2006/03 [Refereed]
     
    Infrared-induced alignment change of liquid crystal domains was investigated for plastic columnar mesophase of a liquid crystalline triphenylene derivative. A homeotropic alignment change of domains was observed when a circularly polarized infrared light with the same wavelength was irradiated. The results strongly imply that the infrared irradiation is a possible technique for device fabrication by use of plastic columnar mesophase as a liquid crystalline semiconductor. (c) 2005 Elsevier B.V. All rights reserved.
  • H Monobe; N Terasawa; Y Shimizu; K Kiyohara; M Heya; K Awazu
    Mol. Cryst. Liq. Cryst. TAYLOR & FRANCIS LTD 437 1325 - 1332 1542-1406 2005/05 [Refereed]
     
    In this study, alignment change of liquid crystal domains induced by infrared irradiation was investigated for a plastic hexagonal columnar mesophase of a liquid crystalline triphenylene derivative. A uniform and anisotropic alignment change of domains was observed when polarized infrared light corresponding to the wavelength of the aromatic C-C stretching absorption band of triphenylene core was irradiated. The results strongly imply that the infrared irradiation is a possible technique for device fabrication by use of plastic columnar mesophase as a liquid crystalline semiconductor.
  • Y Shimizu; H Monobe; M Heya; K Awazu
    Mol. Cryst. Liq. Cryst. TAYLOR & FRANCIS LTD 441 287 - 295 1542-1406 2005/05 [Refereed]
     
    Recent findings were briefly described for the liquid crystal alignment change under the polarized infrared laser irradiation using an free electron laser (FEL), which causes the excitation of vibrational mode of chemical bond in the mesogen. For hexagonal columnar (Col(h)) mesophase of hexahexyloxytriphenylene (C6OTP), a new domain with a certain uniformity of molecular alignment could be attained, in which one can control the director orientation in the combination of the polarization direction of the incidence and the direction of the transition dipole moment for the vibrational excitation. This phenomenon is not observed for the relatively lower-ordered liquid crystals with the lower viscosity such as discotic nematic (N-D) phase as well as nematic (N) and smectic A/C (SmA/SmC) phases of calamities, It could be expected that the polarized infrared irradiation gives a novel technique of domain control of the highly viscous mesophase, which is applicable to a fabrication of organic devices by use of liquid crystalline materials for electronics.
  • Y Shimizu; H Monobe; M Heya; K Awazu
    Mol. Cryst. Liq. Cryst. TAYLOR & FRANCIS LTD 443 49 - 58 1542-1406 2005/05 [Refereed]
     
    Recently a new phenomenon was found that the change of liquid crystal alignment for hexagonal columnar (Col(h) ) mesophase is realized under the polarized infrared laser irradiation using an free electron laser (FEL) via the vibrational mode excitation of a chemical bond in the mesogen. For Col(h) mesophase of hexahexyloxytriphenylene (C6OTP), a new domain with a certain uniformity of molecular alignment could be obtained and one can control the director orientation based on the selected combination of the polarization direction of the incidence and the direction of the transition dipole moment for the vibrational excitation. This phenomenon could be observed only for the relatively higher-ordered liquid crystals with the higher viscosity such as Col(h) mesophase not for discotic nematic as well as calamitic nematic and smectic A/C phases, meaning it could be good for the liquid crystalline semiconductors for the fabricating organic devices.
  • H Monobe; Y Shimizu; M Heya; K Awazu
    Mol. Cryst. Liq. Cryst. TAYLOR & FRANCIS LTD 443 211 - 217 1542-1406 2005/05 [Refereed]
     
    Infrared photoinduced change of discotic liquid crystal domains was investigated for a hexagonal columnar mesophase of a triphenylene derivative with three wavelengths of irradiation. The formation of uniform domains was observed under the irradiation with the wavelength of certain absorption bands of the compound. The technique could provide a novel technology to control the columnar alignment of viscous mesophase materials.
  • UCHIZONO Takeyuki; HEYA Manabu; AWAZU Kunio; SUNADA Kazuhisa; YOSHIKAWA Kazushi; INOUE Masayoshi
    日本レーザー医学会誌 25 (4) 265 - 272 0288-6200 2005/01 [Refereed]
  • 特集「歯科におけるレーザー応用の現状」－基礎 レーザーと生体硬組織の相互作用－
    部谷学; 内園岳志; 粟津邦男
    日本レーザー医学会誌 25 323 - 331 2005/01 [Refereed]
  • IWAMOTO Yumiko; HEYA Manabu; NAGATA Hiroyuki; NISHIDA Yuji; HASHISHIN Yuichi; AWAZU Kunio
    IEEJ Transactions on Electronics, Information and Systems The Institute of Electrical Engineers of Japan 124 (11) 2215 - 2220 0385-4221 2004/11 [Refereed]
     
    For low-invasive laser treatment, stable absorption properties of tissue during laser treatment are essentially needed, which enable us to predict irradiation effect (ablation depth, thermally-altered depth) using them. There are water and proteins as main absorber in the mid-infrared range. During laser treatment, the absorption properties of soft tissue are changed due to laser-induced temperature rise and leading to the induction of unexpected irradiation effects. We have proposed and demonstrated a novel, low-invasive laser surgery with 6.1-μm-light irradiation. 6.1-μm-light can resonantly excite both OH bending (water) and amide-I (proteins). The absorption properties of soft tissue during laser treatment would be come considerably stable because they do not remarkably depend on the surrounding temperature and the water concentration. We examined the gelatin ablation properties by λ=6.1-μm irradiation using a tunable mid-infrared Free-Electron Laser and showed that λ=6.1-μm irradiation is one of the candidates for a low-invasive soft tissue incision. Gelatins were used as a model substrate for soft tissue. From these experiments, it was found as follows. (1) Enhanced gelatin ablation occurred near λ=6.1-μm, but not λ=6.45-μm (Amide II of proteins). (2) The gelatins were removed due to water vaporization, which is reflected in the static absorption properties of the gelatin before laser irradiation. Thus, we showed the applicability of λ=6.1-μm -light for a new light source to realize a low-invasive soft tissue incision.
  • IWAMOTO Yumiko; HEYA Manabu; HASHISHIN Yuichi; AWAZU Kunio; HORIIKE Hiroshi
    Nippon Laser Igakkaishi Japan Society for Laser Surgery and Medicine 25 (3) 135 - 146 0288-6200 2004/10 [Refereed]
     
    In order to demonstrate basically the usefulness of 6.05-μm-light as the light source for non-invasive soft tissue cutting, we have preliminarily conducted gelatin ablation experiments using a tunable mid-infrared Free Electron Laser (MIR-FEL). It is essential for non-invasive cutting to enable us to precisely predict irradiation effects (such as ablation and denaturation depths) before laser treatment. 6.05-μm-light can resonantly excite both the OH bending of water and the amide-I of proteins. Wet gelatins (including 80-wt% water concentration) were used as the model substance of soft tissue, which consists of 80-wt% water and 20-wt% proteins. The MIR-FEL wavelength was varied within the wavelength range of 5.6-6.7 μm. The incident laser energy density was fixed at 3.6±0.3 J/cm2. The exposure time was 10 s or 100 s. The structural changes of irradiated gelatins were observed with an optical microscope coupled to a CCD camera. The followings can be derived from these observations. (1) Efficient gelatin ablation occurred around 6.05 μm but not 6.45 μm (corresponding to the amide-II of proteins). (2) In the case of 6.05 μm, the wet gelatins were removed due to the pure vaporization of water according to the absorption properties of the wet gelatins before laser treatment, resulting to a predictable laser treatment. In addition, the denaturated area of the gelatins remarkably decreased due to a spectral shift from the OH bending to the amide-I in the absorber as the exposure time is increased (the water in the irradiated gelatins is depleted), leading to the prevention of the formation of thermal coagulum. Thus, 6.05-μm-light can remove predictably soft tissue without unexpected effects and also prevent the formation of undesirable thermal coagulum even if the water concentration remarkably declines. We have proved that 6.05-μm-light is one of the candidates for a predictable soft tissue cutting and/or surgery.
  • M Heya; T Saiki; K Tsubakimoto; K Awazu; M Nakatsuka
    Nucl. Instr. and Meth. in Phys. Res. A ELSEVIER SCIENCE BV 528 249 - 253 0168-9002 2004/08 [Refereed]
     
    In order to generate a flat-topped beam profile from a tunable, broadband, mid-infrared free-electron laser (MIR-FEL), we have proposed and designed a dimple mirror system (DMS), using a laser optics calculation code LOCCO. The principles of the DMS are similar to those of a micro-lens array system involving a principal focusing lens and a two-dimensional (2D) array of micro-lenses located ahead of the principal lens. The DMS is composed of a parabolic mirror, which acts as the principle lens and a 2D array of micro-dimples, which splits the incident FEL beam into many partial beams. All beamlets overlap near the focal point of the parabolic mirror, resulting in the generation of an approximately flat-topped intensity profile due to the interference of light. We proved that the DMS can generate a flat-topped profile even over a wide MIR waveband. Thus, we showed the applicability of the DMS for uniform illumination from a tunable, broadband MIR-FEL. (C) 2004 Elsevier B.V. All rights reserved.
  • SANO Shu; HEYA Manabu; TAKAGI Nobuhiko; FUKAMI Yuko; HASHISHIN Yuichi; AWAZU Kunio
    IEEJ Transactions on Electronics, Information and Systems The Institute of Electrical Engineers of Japan 124 (6) 1234 - 1243 0385-4221 2004/06 [Refereed]
     
    Surface modification of root dentin by mid-infrared (MIR) pulsed-laser irradiation is one of the candidates for a novel, non-invasive treatment to prevent root surface caries. To modify root dentin effectively and non-invasively it is essential to estimate quantitatively and qualitatively the laser parameters, such as the wavelength and the power density, required for surface modification. The key aspect is to bring about effective surface modification of root dentin while minimizing the unwanted removal of the underlying dentin. Using a tunable, MIR Free Electron Laser (FEL) in the wavelength region of 8.8-10.6 μm, we have investigated macroscopically the extent of surface modification (morphological and chemical changes) of root dentin. We have obtained experimental results related to the ablation depth, the MIR absorption spectrum, and the elemental chemical composition of the irradiated dentin. The observations showed that the surface modification of root dentin was inclined toward well-recrystallized, HAp-like material, leading to an increase in the acid resistance and dentinal tubule sealing. The laser parameters, at which efficient surface modification without enhanced ablation occurred, were estimated to be at λ= - 9.0 μm or - 9.7 μm and in the average power density region of - 10-20 W/cm2 (resulting in energy density per macropulse and peak power density regions of - 1-2 J/cm2 and - 66.7-133.3 kW/cm2). Thus, it was found that the surface modification of root dentin strongly depends on the laser conditions applied. We conclude that the optimum laser wavelengths for (1) root surface caries treatment without restorative procedure and (2) hard tissue ablation without water irrigation are around (1) λ= 9.0 μm or 9.7 μm and (2)λ= 9.0 μm in the absorption bands due to P-O stretching, respectively.
  • H Monobe; K Kiyohara; Y Shimizu; M Heya; K Awazu
    Mol. Cryst. Liq. Cryst. TAYLOR & FRANCIS LTD 410 557 - 566 1058-725X 2004/05 [Refereed]
     
    Polarized infrared photoinduced change of liquid crystal domains was investigated for a hexagonal columnar phase of a liquid crystalline triphenylene derivative. A uniform and anisotropic change of domains was observed when a polarized infrared light corresponding to the wavelength of the absorption band of triphenylene core was irradiated. IR absorption dichroism is induced as a result of the reorientation of triphenylene core. The texture observation and polarized microscopic FT-IR spectra show that a change of the molecular alignment occurred and the direction of columns depends on the polarization direction of an actinic infrared light. The technique could provide a novel technology to control the columnar alignment of supra-molecular systems.
  • H Monobe; K Kiyohara; N Terasawa; M Heya; K Awazu; Y Shimizu
    Adv. Funct. Mater. WILEY-V C H VERLAG GMBH 13 (12) 919 - 924 1616-301X 2003/12 [Refereed]
     
    The infrared photoinduced alignment change of liquid-crystal domains was investigated for a hexagonal columnar mesophase of a liquid-crystalline triphenylene derivative. A uniform and anisotropic alignment change of domains was observed when a polarized infrared (IR) light corresponding to the wavelength of the aromatic C-C stretching absorption band of the triphenylene core was used to irradiate the sample. The relationship between the aligned azimuthal angle of the columnar axis and the polarization of the IR incident irradiation was investigated. IR absorption dichroism is induced as a result of the reorientation of triphenylene core. Texture observation and polarizing microscope FTIR spectra show that a change of the molecular alignment occurred and that the direction of columns depends on the polarization angle of the IR light used for irradiation. The mechanism of the alignment change in a columnar liquid crystal film by IR irradiation is also discussed. The technique could provide a novel technology to control the columnar alignment of highly viscous liquid crystals.
  • 部谷学; 内園岳志; 佐野秀; 石井克典; 岩本由美子; 熊崎洋晃; 鈴木-吉橋幸子; 粟津邦男
    レーザー研究 レ-ザ-学会 31 (12) 805 - 810 0387-0200 2003/12 [Refereed]
  • H Monobe; K Kiyohara; N Terawasa; M Heya; K Awazu; Y Shimizu
    Chem. Lett. CHEMICAL SOC JAPAN 32 (9) 870 - 871 0366-7022 2003/09 [Refereed]
     
    Infrared photoinduced alignment change of liquid crystal domains was investigated and a uniform and anisotropic change of domains was observed. The texture observation and polarized microscopic IR spectra show that a change of the molecular alignment occurred and the direction of columns depends on the polarizing angle of an irradiating infrared light.
  • H Monobe; K Kiyohara; N Terasawa; M Heya; K Awazu; Y Shimizu
    Thin Solid Films ELSEVIER SCIENCE SA 438-439 418 - 422 0040-6090 2003/08 [Refereed]
     
    Infrared photo-induced alignment change of liquid crystal domains was investigated for a hexagonal columnar mesophase of liquid crystalline triphenylene derivative. A uniform and anisotropic change of domains was observed when a polarized infrared light corresponding to the wavelength of the absorption band of triphenylene core was irradiated. IR absorption dichroism is induced as a result of the reorientation of triphenylene core part. The texture observation and polarized microscopic FT-IR spectra show that a change of the molecular alignment occurred, and the direction of columns depends on the polarizing angle of an irradiated infrared light. This technique could provide a novel technology to control the columnar alignment of supra-molecular systems. (C) 2003 Elsevier Science B.V. All rights reserved.
  • Y Naito; R Sasaki; M Heya; K Awazu
    J. Mass Spectrom. Soc. Jpn. The Mass Spectrometry Society of Japan 51 (4) 458 - 465 1340-8097 2003/08 [Refereed]
  • M Heya; Y Fukami; H Nagata; Y Nishida; K Awazu
    Nucl. Instr. and Meth. in Phys. Res. A ELSEVIER SCIENCE BV 507 (1-2) 564 - 568 0168-9002 2003/07 [Refereed]
     
    Efficient and precise ablation of soft tissue is needed for non-invasive dermatological and corneal surgeries. Previous research has, revealed that smooth and efficient cutting of certain soft tissues' and gelatin is possible using a Free Electron Laser (FEL) with a wavelength of lambda = 6.45 mum, tuned to the amide-II band of protein. Gelatin ablation experiments have been carried out using a mid-infrared FEL within the waveband lambda = 5.6 - 6.7 mum by changing the primary absorbers such as water (lambda = 6.1 mum) and protein (lambda = 6.45 mum). The gelatin with 80 wt% water was efficiently ablated by FEL irradiation with the waveband lambda = - 5.95-6.19 mum. On the other hand, using irradiation within lambda = similar to 6.4-6.6 mum, many small bubbles were observed in the irradiated volume, and the gelatin was not ablated but significantly melted. Thus, it was found that the most effective wavelength was similar to 6.1 mum, not similar to 6.45 mum, in order to cut soft tissue with a high water concentration at the expense of surface smoothness. (C) 2003 Elsevier Science B.V. All rights reserved.
  • NAGATA Hiroyuki; HEYA Manabu; SANO Shu; UCHIZONO Takeyuki; HASHISHIN Yuichi; AWAZU Kunio
    The Review of laser engineering レ-ザ-学会 31 (5) 342 - 347 0387-0200 2003/05 [Refereed]
  • M Heya; S Sano; N Takagi; Y Fukami; K Awazu
    Lasers Surg. Med. WILEY-LISS 32 (5) 349 - 358 0196-8092 2003/05 [Refereed]
     
    Background and Objectives: Surface modification of root dentin by mid-infrared (MIR) pulsed-laser irradiation is one of the candidates for a novel, non-invasive treatment to prevent root surface caries. To modify root dentin effectively and non-invasively it is essential to estimate quantitatively and qualitatively the laser parameters, such as the wavelength and power density, required for surface modification. The key aspect is to bring about effective surface modification of the root dentin while minimizing the unwanted removal of the underlying dentin. Study Design/Materials and Methods: Using a tunable, MIR Free Electron Laser with lambda = 8.8-10.6 mum, we have investigated macroscopically the extent of the surface modification (morphological and chemical changes) of root dentin. We have obtained experimental results related to the ablation depth, the MIR absorption spectrum, and the elemental chemical composition. Results: The observations showed that the surface modification of root dentin was inclined toward well-recrystallized HAp-like material, leading to an increase in the acid resistance and dentinal tubule sealing. The laser parameters, at which efficient surface modification without enhanced ablation occurred, were estimated to be approximately in the wavelength region around lambda = similar to9.0 or similar to9.7 mum and in the average power density region of similar to10-20 W/cm(2) (resulting in total energy density and peak power density regions of similar to1-2 kJ/cm(2) and similar to0.67-1.2 kW/cm(2)). Conclusions: The surface modification of root dentin strongly depends on the laser parameters applied. We conclude that the optimum wavelengths for laser treatment of root surface caries are lambda = similar to9.0 or similar to9.7 mum, corresponding to the absorption peak due to P-O stretching.
  • H Monobe; K Kiyohara; M Heya; K Awazu; Y Shimizu
    Mol. Cryst. Liq. Cryst. TAYLOR & FRANCIS LTD 397 359 - 365 1542-1406 2003/05 [Refereed]
     
    An infrared technique for molecular alignment control of discotic columnar liquid crystals is described. The liquid crystal domain change was induced in hexagonal columnar mesophase by infrared irradiation with a vibrational excitation of the chemical bonds in the triphenylene mesogen. In the new domain a uniform alignment of molecules was attained and the behaviour is essentially related to the polarisation of the incident beam. Also the new domain is quite stable, though depending on temperature. However, such a new domain formation was not observed in the discotic nematic phase.
  • Dynamics of low coupling parameter Free-Electron Laser oscillator
    H Nishiyama; M Asakawa; Y Tsunawaki; M Heya; K Awazu; K Imasaki
    Nucl. Instr. and Meth. in Phys. Res. A 507 74 - 78 2003/03 [Refereed]
     
    中赤外自由電子レーザーの発振ダイナミクスを理解するために、自由電子レーザーの出力と発振器長の関係を実験的、解析的に調べた。その結果、共振器長を長く設定することで、自由電子レーザーの出力が安定化することが分かった。
  • Yasuhide NAITO; Rie SASAKI; Manabu HEYA; Kunio AWAZU
    レーザー研究 Laser Society of Japan 31 (3) 219 - 224 0387-0200 2003/03 [Refereed]
  • MOCHIZUKI-ODA Noriko; KATAOKA Yosky; CUI Yilong; TAMURA Yasuhisa; YAMADA Hisao; HEYA Manabu; AWAZU Kunio
    レーザー研究 レ-ザ-学会 30 (9) 542 - 545 0387-0200 2002/09 [Refereed]
  • S Fujioka; H Shiraga; M Nishikino; M Heya; K Shigemori; M Nakai; H Azechi; S Nakai; T Yamanaka
    Rev. Sci. Instrum. AMER INST PHYSICS 73 (7) 2588 - 2596 0034-6748 2002/07 [Refereed]
     
    One-dimensional (1D) penumbral imaging technique with high spatial resolution has been developed, and applied to density profile measurements in laser-driven Rayleigh-Taylor instability experiments at a GEKKO XII-HIPER laser system. A laser-irradiated planar target was observed with side-on x-ray backlighting. A penumbral image of an x-ray radiograph was made by using a knife-edge imager. The x-ray radiograph was, then, reconstructed by differentiating the penumbral image with a proper Wiener filtering. A density profile was deduced from the reconstructed x-ray radiograph. In a proof-of-principle experiment, the density profile of a polystyrene (PS) target before laser irradiation was measured by using this method, and high spatial resolution of 3-4 mum was demonstrated. A laser-irradiated PS target in the acceleration phase was observed. The experimentally observed density profile was found to be consistent with the prediction by a 1D hydrodynamic simulation code. The x-ray penumbral imaging is a very simple and useful technique with high spatial resolution for research in hydrodynamics relevant to inertial fusion energy. (C) 2002 American Institute of Physics.
  • N Mochizuki-Oda; Y Kataoka; YL Cui; H Yamada; M Heya; K Awazu
    Neuroscience Letters ELSEVIER SCI IRELAND LTD 323 (3) 207 - 210 0304-3940 2002/05 [Refereed]
     
    Low-power, near-infra-red laser irradiation has been used to relieve patients from various kinds of pain, though the precise mechanisms of such biological actions of the laser halve not yet been resolved. To investigate the cellular mechanisms by near-infra-red laser on the nervous system, we examined the effect of 830-nm laser irradiation on the energy metabolism of the rat brain. The diode laser was applied for 15 min with an irradiance of 4.8 W/cm(2). Tissue adenosine triphosphate (ATP) content of the irradiated area in the cerebral cortex was 19% higher than that of the non-treated area, whereas the adenosine diphosphate (ADP) content showed no significant difference. Laser irradiation at another wavelength (652 nm) had no effect on either ATIP or ADP contents. The temperature of the tissue was increased by 4.4-4.7 degreesC during the irradiation of both wavelengths. These results suggest that the increase in tissue ATP content did not result from the thermal effect, but from a specific effect of the laser operated at the 830-nm wavelength. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.
  • M Heya; H Nagata; Y Fukami; K Awazu
    Jpn. J. Appl. Phys., Suppl. 41-1 (41) 138 - 142 2002/02 [Refereed]
     
    水を吸収体としてレーザー治療を行う場合、照射中の水の吸収特性変化が治療の安全性に影響を及ぼす。照射中に吸収特性が変化しないことは、治療の安全性につながる。軟組織のレーザーメスとして期待されている波長6.1μm（OH変角振動モード・アミド-I）近傍に対する水の吸収特性を光音響法によって測定した。その結果、6.1μm近傍の吸収特性は照射中の温度変化の影響を受けにくいことを明らかにした。
  • M Heya; Y Fukami; K Awazu
    Jpn. J. Appl. Phys.，Suppl. INST PURE APPLIED PHYSICS 41 (1) 143 - 147 0021-4922 2002/02 [Refereed]
     
    A micropulse-picking system (UPS) attached to a Free Electron Laser (FEL) is a useful tool for non-invasive bio-molecular surgery research in the mid-infrared (MIR) region. The key to the realization of non-invasive bio-molecular surgery techniques is to avoid excessive heating effects around the irradiated tissues, and then to excite effectively and efficiently only those laser-tissue interactions of interest. We can easily control the heating effects by changing the micropulse structure of the MIR-FEL by means of an MPS. We have developed and improved a system that incorporates two germanium acousto-optic modulators, which can deflect the FEL beam effectively at any given time by using the Bragg diffraction technique. We have demonstrated a proof-of-concept experiment with an NOS over the range between 5.5 mum and 11 mum, and we have estimated the picking efficiency. Such a MIR region includes the important absorption bands in soft (protein and water) and hard (apatite) tissues. The efficiency was above similar to50% in the range from 5.5-10.0 mum, without any consideration of the Fresnel reflection losses at the surfaces of the Ge crystal.
  • H Horiike; N Tsubouchi; K Awazu; M Asakawa; M Heya
    Jpn. J. Appl. Phys.，Suppl. INST PURE APPLIED PHYSICS 41 (1) 10 - 14 0021-4922 2002/02 [Refereed]
     
    Institute of Free-Electron Laser is one of the FEL supplying facilities for 2000 hours in a-year. The FEL system consists of two RF-linacs and five wigglers, and covers the wavelength range from 0.28 to 100 pm. In the operational period from April 2001 to March 2002, the mid-infrared light of 5 to 20 mum was supplied for over 40 cooperative research programs on fields of semiconductor, bio-medical and environmental chemistry An effort is still carrying on to improve the property of the light.
  • Y Fukami; M Heya; H Matsubara; K Awazu
    Jpn. J. Appl. Phys.，Suppl. INST PURE APPLIED PHYSICS 41 (1) 132 - 137 0021-4922 2002/02 [Refereed]
     
    Cholesteryl ester is a compound of cholesterol and fatty acid,, and is highly accumulated in arteriosclerosis regions and gallstones. We have studied irradiation effects of mid-infrared free electron laser (MIR-FEL) on cholesterol ester. In order to search optimum laser conditions for efficient removal of cholesterol ester, we tuned the FEL wavelengths to 5.75 (ester bond) and 6.82 mum (methylene bond), and irradiated cholesteryl oleate, a kind of cholesterol esters. The average power density was varied in the range of 1-10 W/cm(2). Each irradiated sample was analyzed using a mass spectrometer to examine products after irradiation and obtain efficiencies of ester dissociation. The results indicate that (1) ester bond of cholesteryl oleate was dissociated to generate cholesterol and oleic acid, (2) irradiation products and dissociation efficiency of ester bond were similar regardless of the vibration modes which absorbs irradiated wavelength of MIR-FEL, and (3) the laser induced effects were considered to be thermal effects without accompanying thermal diffusion.
  • Y Shimizu; H Monobe; M Heya; K Awazu
    Jpn. J. Appl. Phys.，Suppl. INST PURE APPLIED PHYSICS 41 (1) 104 - 107 0021-4922 2002/02 [Refereed]
     
    It was found that the vibrational excitation of columnar liquid crystalline compounds leads to the change of liquid crystalline alignment for a columnar mesophase. This is a quite new phenomenon for the alignment change of liquid crystals. The studies on conventional rod-like liquid crystals implied that this is good for highly ordered thus highly viscous liquid crystals for the alignment control. The infrared laser systems which are wavelength-tunable may make it possible to develop a new method for a micro/nano-fabrication technology for organic functional devices including materials with highly ordered mesophase.
  • 部谷学; 深見裕子; 粟津邦男
    光学 応用物理学会分科会日本光学会 30 (10) 667 - 672 0389-6625 2001/10 [Refereed]
  • M Heya; H Shiraga; A Sunahara; M Nakasuji; M Nishikino; H Honda; K Fujita; N Izumi; N Miyanaga; H Nishimura; H Azechi; S Naruo; H Takabe; T Yamanaka; K Mima
    Laser and Particle Beams CAMBRIDGE UNIV PRESS 19 (2) 267 - 284 0263-0346 2001/06 [Refereed]
     
    Effects of an implosion nonuniformity with l = 1 (l: Legendre polynomial mode number) on the hot spark formation were investigated in a series of direct-drive implosion experiments at the Gekko-XII glass laser (Yamanaka et al., 1987). The implosion dynamics and the performance from the early to final stage of the implosion were observed with a variety of X-ray imaging and neutron diagnostics. A drive nonuniformity in the implosion with l = 1 was observed in the shape of the accelerated target at the early stage of the implosion At the final stage of the implosion, the resultant nonuniformity with l = 1 was also observed as a geometrical shift of core plasmas from the center of the chamber. The observed neutron yield and X-ray emission properties at the final stage of the implosion were significantly degraded with an increase of the implosion nonuniformity, with l = 1. The experimental results were compared with one-dimensional (I-D) and two-dimensional (2-D) hydrodynamic simulations. As a result, it was found that the implosion nonuniformity with l = 1 shifts the whole implosion dynamics towards its direction and prevents the confinement of the gas fuel considerably. However, the experimentally observed degradation in the hot spark formation, such as reductions in neutron yield and features in X-ray emission, can be reproduced in 2-D simulations not with an asymmetric perturbation of l = 1 only,but with multimode nonuniformities such as l = 1 coupled with some additional middle-mode ones (e.g., l = 6). Such a complex spike structure caused by the multimode nonuniformities was found to be essential for the experimentally observed rapid cooling of the hot spark.
  • M Heya; S Fujioka; H Shiraga; N Miyanaga; T Yamanaka
    Rev. Sci. Instrum. AMER INST PHYSICS 72 (1) 755 - 758 0034-6748 2001/01 [Refereed]
     
    In order to enlarge the field of view of a multi-imaging x-ray streak (MIXS) camera technique [H. Shiraga , Rev. Sci. Instrum. 66, 722 (1995)], which provides two-dimensionally space-resolved x-ray imaging with a high temporal resolution of similar to 10 ps, we have proposed and designed a wide-field MIXS (W-MIXS) by increasing the number of image-sampling arrays. In this method, multiple cathode slits were used on the photocathode of an x-ray streak camera. The field of view of the W-MIXS can be enlarged up to 150-200 mum instead of similar to 70 mum for a typical MIXS with a spatial resolution of similar to 15 mum. A proof-of-principle experiment with the W-MIXS was carried out at the Gekko-XII laser system. A cross-wire target was irradiated by four beams of the Gekko-XII laser. The data streaked with the W-MIXS system were reconstructed as a series of time-resolved, two-dimensional x-ray images. The W-MIXS system has been established as an improved two-dimensionally space-resolved and sequentially time-resolved technique. (C) 2001 American Institute of Physics.
  • KA Tanaka; R Kodama; N Izumi; K Takahashi; M Heya; H Fujita; Y Kato; Y Kitagawa; K Mima; N Miyanaga; T Norimatsu; Y Sentoku; A Sunahara; H Takabe; T Yamanaka; T Koase; T Iwatani; F Ohtani; T Miyakoshi; H Habara; M Tanpo; S Tohyama; FA Weber; TW Barbee; LB Dasilva
    Comptes Rendus De Lacademie Des Sciences Serie IV Physique Astrophysique EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER 1 (6) 737 - 744 1296-2147 2000/08 [Refereed]
     
    At the Institute of Laser Engineering, various type of experiments related to fast ignition were performed with the 12-beam laser system GEKKO XII and the newly added 100 TW beams line. Using both X-ray and UV laser probes, drilling via ponderomotive laser light self-focusing was studied to show drilling well into the overdense plasma over a distance of 100 mum at a self-focused laser intensity of 10(18) W/cm(2). This type of self-focusing accelerated electrons up to 0.1 to 1 MeV and was also applied to an imploding shell. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.
  • Studies of ultra-intense laser plasma interactions for fast ignition
    K A Tanaka; R Kodama; H Fujita; M Heya; N Izumi; Y Kato; Y Kitagawa; K Mima; N Miyanaga; T Norimatsu; A Pukhov; A Sunahara; K Takahashi; M Allen; H Habara; T Iwatani; T Matushita; T Miyakoshi; M Mori; H Setoguchi; T Sonomoto; M Tanpo; S Tohyama; H Azuma; T Kawasaki; T Komeno; O Maekawa; S Matsuo; T Shozaki; K Suzuki; H Yoshida; T Yamanaka; Y Sentoku; F Weber; T W Barbee Jr; L DaSilva
    Physics of Plasmas 7 2014 - 2022 2000/04 [Refereed]
  • H Nishimura; H Shiraga; H Azechi; N Miyanaga; M Nakai; N Izumi; M Nishikino; M Heya; K Fujita; Y Ochi; K Shigemori; N Ohnishi; M Murakami; K Nishihara; R Ishizaki; H Takabe; K Nagai; T Norimatsu; M Nakatsuka; T Yamanaka; S Nakai; C Yamanaka; K Mima
    Nucl. Fusion 40 (3Y) 547 - 556 2000/03 [Refereed]
  • 部谷学; 白神宏之; 島田京子; 宮永憲明; 高部英明; 山中龍彦; 三間圀興
    プラズマ・核融合学会誌 プラズマ・核融合学会 75 (5) 105 - 118 1999/05 [Refereed]
     
    爆縮の最終段階でのコアプラズマからのX線発光を時間,二次元空間分解して計測を行うために,X線ストリークカメラに画像サンプリング技術を応用したマルチイメージングX線ストリークカメラ(MIXS)法,マルチチャンネルMIXS(McMIXS)法を超高速二次元X線画像技術として開発した. 得られた爆縮コアプラズマの二次元X線および電子温度分布は時間的に連続して変化する二次元画像となっており,その時間発展を動画的描画手法を用いて記述することが有効である. 動画化することにより,時間的,空間的に変化している爆縮コアプラズマのダイナミクスをより直観的,効果的に理解することができ,爆縮の最終段階のコア内部でのホットスパークの形成過程を実験的に評価することが可能となった. このようにレーザー爆縮コアプラズマダイナミクスの研究を進める上で,動画的描画手法を用いた超高速二次元X線画像計測技術が爆縮コアプラズマ診断において有力な診断技術の一つであることを示した.
  • H Shiraga; M Nakasuji; M Heya; N Miyanaga
    Rev. Sci. Instrum. AMER INST PHYSICS 70 (1) 620 - 623 0034-6748 1999/01 [Refereed]
     
    Ultrafast two-dimensional (2D) x-ray imaging with a temporal resolution better than 10 ps is of great importance in diagnosing the final stages of the imploded core plasmas of inertial confinement fusion (ICF) targets. The multi-imaging x-ray streak camera (MIXS) has been one of such imaging techniques. Recently, we have proposed another scheme, a 2D sampling-image x-ray streak camera method (2D-SIXS). In this scheme, a 2D image is sampled two dimensionally with a set of sampling points distributed regularly over the whole image on a cathode plate of an x-ray streak camera. The sampled image is streaked, and then, reconstructed to form the time-resolved 2D images like movie pictures. In this article, we report results of our proof-of-principle experiments of 2D-SIXS scheme performed at Gekko-XII glass laser system. A gold-coated spherical target was irradiated by three beams (0.53 mu m) of Gekko-XII laser. Streaked data of 2D-SIXS were obtained and a series of time-resolved 2D x-ray images were successfully reconstructed. 2D-SIXS is suitable for very fast, short-lived, and small x-ray sources such as a hot spark in the ICF plasma as well as short-pulse-laser-produced plasmas. (C) 1999 American Institute of Physics. [S0034-6748(99)55201-5].
  • H Nishimura; H Azechi; H Shiraga; M Nakai; N Miyanaga; H Takabe; T Norimastu; H Fujita; K Shigemori; M Heya; S Izumi; H Honda; K Fujita; A Sunahara; M Honda; T Kanabe; T Jitsuno; M Takagi; R Kodama; KA Tanaka; M Nakatsuka; K Nishihara; Y Kato; T Yamanaka; S Nakai; K Mima
    Plasma Physics and Controlled Fusion IOP PUBLISHING LTD 39 (5A) 401 - 409 0741-3335 1997/05 [Refereed]
     
    The irradiation uniformity of the GEKKO XII laser has been improved by implementing the state-of-the-art beam smoothing and laser control techniques in the system. Non-uniformity modes higher than 20 are improved to less than 1% RMS by introducing partially coherent light, while the lower modes are improved to 3-4% RMS. Implosion experiments were carried out with the new GEKKO XII: a fast-rise square pulse preceded by a pre-pulse was used to suppress the Rayleigh-Taylor instability at the acceptable expense of implosion efficiency. The experimental results are compared with a pusher-fuel mixing model combined with a one-dimensional hydrodynamic simulation. The degradation of experimentally obtained neutrons is mainly attributed to the lower-mode asymmetry. Recent results of planar target experiments on hydrodynamic instabilities are also presented. Particular emphasis is given to the noticeable reduction of fluid instability by the flushing of an external x-ray over the target surface prior to the main drive pulse, leading to suppression of the initial imprint amplitude by the pre-formed plasma.
  • M Heya; M Nakasuji; H Shiraga; N Miyanaga; H Azechi; H Takabe; T Yamanaka; K Mima
    Rev. Sci. Instrum. AMER INST PHYSICS 68 (1) 820 - 823 0034-6748 1997/01 [Refereed]
     
    We have developed a multichannel, multiimaging x-ray streak camera technique to measure two-dimensional electron-temperature distributions with a high temporal resolution by adding a multichannel spectrum selection capability to a multiimaging x-ray streak camera technique, and applied it to direct-drive implosion experiments with partially coherent light at Gekko-XII laser facility. It was found that electron-temperature distributions in the laser-imploded core plasmas of ICF targets had low-mode nonuniform structures changing with a temporal scale of 20 ps, and the abrupt drop of the electron temperature appeared in the deceleration phase. We have compared temporal profiles of the experimentally observed x-ray intensity and electron-temperature with those predicted by a one-dimensional hydrodynamic code ''ILESTA'' to investigate the hot spark heating in the core plasmas. (C) 1997 American Institute of Physics.
  • H Shiraga; M Heya; M Nakasuji; N Miyanaga; H Azechi; H Takabe; T Yamanaka; K Mima
    Rev. Sci. Instrum. AMER INST PHYSICS 68 (1) 828 - 830 0034-6748 1997/01 [Refereed]
     
    One- (1D) and two-dimensional (2D) x-ray imaging techniques with x-ray streak cameras have been developed and utilized for investigating implosion dynamics of laser fusion targets. Conventional streaked 1D images of the shell motion of the imploding target was recorded together with the time-resolved 2D multi-imaging x-ray streak images of the core shapes on the same x-ray streak camera. Precise comparison of the core dynamics between the experimental and simulation results was performed with an accuracy of 30 ps by fitting the trajectories of the x-ray emission from the imploding shell. (C) 1997 American Institute of Physics.
  • H Shiraga; N Miyanaga; M Heya; M Nakasuji; Y Aoki; H Azechi; T Yamanaka; K Mima
    Rev. Sci. Instrum. AMER INST PHYSICS 68 (1) 745 - 749 0034-6748 1997/01 [Refereed][Invited]
     
    Ultrafast two-dimensional x-ray imaging is required for diagnosing laser-driven inertial confinement fusion plasmas. Image sampling technique with x-ray streak cameras can meet this requirement. Multi-imaging x-ray streak camera method (MIXS) with temporal and spatial resolutions of 10 ps and 15 mu m, respectively, has been developed and successfully utilized for diagnosing the uniformity and heating process of the imploded core plasmas. The two-dimensional sampling-image x-ray streak camera method is also presented. Two types of spectroscopic applications of the MIXS have been developed recently. One is multichannel MIXS, which has three MIXS channels with various spectral responses for time-resolved two-dimensional temperature measurement of the plasmas. Another is monochromatic MIXS for temperature, density, and mixing measurement, in which monochromatic images with Bragg crystals are coupled to MIXS. (C) 1997 American Institute of Physics.
  • N Miyanaga; Y Aoki; H Shiraga; K Shimada; K Fujimoto; M Heya; M Nakasuji
    Rev. Sci. Instrum. AMER INST PHYSICS 68 (1) 817 - 819 0034-6748 1997/01 [Refereed]
     
    To prepare a new diagnostic tool for the laser-imploded plasma, we have developed a time-resolved, two-dimensional monochromatic imaging system that consists of a pinhole array, a flat diffraction crystal, and an x-ray streak camera without cathode slit. We have successfully reconstructed time-resolved two-dimensional images of an Ar resonance line emitted from an imploded plastic shell filled with D-2/Ar mixture gas. The current system provides the temporal resolution of similar to 24 ps and the spatial resolution of similar to 16 mu m for the direction perpendicular to the spectral dispersion. The spatial resolution parallel to the spectral dispersion is less than or equal to 27 mu m, that depends on the crystal broadening and the spectral linewidth. (C) 1997 American Institute of Physics.
  • H Shiraga; M Heya; M Nakasuji; T Yamanaka; Y Kato
    J. Electr. Spectr. Relat. Phenom. ELSEVIER SCIENCE BV 80 287 - 290 0368-2048 1996/05 [Refereed]
     
    2-dimensional x-ray imaging of the laser fusion target is now possible with 10-ps temporal resolution by using recently developed multi-imaging x-ray streak (MIXS) technique. Structures in the x-ray image of the laser-imploded core,symmetry and size, were found to be rapidly changing with 10-ps time scale.
  • K A Kazuo; T Yamanaka; K Nishihara; T Norimatsu; N Miyanaga; H Shiraga; M Nakai; Y Kitagawa; R Kodama; T Kanabe; H Azechi; M Heya; T Jitsuno; M Kado; K Mima; M Nakatsuka; A Nishiguchi; H Takabe; M Takagi; K Tsubakimoto; M Tsukamoto; Y Kato; Y Izawa; S Nakai
    Phys. Plasmas AMER INST PHYSICS 2 (6) 2495 - 2503 1070-664X 1995/06 [Refereed]
  • H Shiraga; M Heya; A Fujishima; O Maegawa; K Shimada; Y Kato; T Yamanaka; S Nakai
    Rev. Sci. Instrum. AMER INST PHYSICS 66 (1) 722 - 724 0034-6748 1995/01 [Refereed]

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