Manabu Heya

Effects of near-infra-red laser irradiation on adenosine triphosphate and adenosine diphosphate contents of rat brain tissue

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 have 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 ATP or ADP contents. The temperature of the tissue was increased by 4.4-4.7 degrees C 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.

Studies of ultra-intense laser plasma interactions for fast ignition

Laser plasma interactions in a relativistic parameter regime have been intensively investigated for studying the possibility of fast ignition in inertial confinement fusion (ICF). Using ultra-intense laser systems and particle-in-cell (PIC) simulation codes, relativistic laser light self-focusing, super hot electrons, ions, and neutron production, are studied. The experiments are performed with ultra-intense laser with 50 J energy, 0.5–1 ps pulse at 1053 nm laser wavelength at a laser intensity of 1019 W/cm2. Most of the laser shots are studied under preformed plasma conditions with a 100 μm plasma scale length condition. In the study of laser pulse behavior in the preformed plasmas, a special mode has been observed which penetrated the preformed plasma all the way very close to the original planar target surface. On these shots, super hot electrons have been observed with its energy peak exceeding 1 MeV. The energy transport of the hot electrons has been studied with making use of Kα emissions from a see...

TWO-DIMENSIONAL SAMPLING-IMAGE X-RAY STREAK CAMERA FOR ULTRAFAST IMAGING OF INERTIAL CONFINEMENT FUSION PLASMAS

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 μm) of Gekko-XII laser. Streaked data of 2D-SIXS were obtained and a series of time-resolved 2D x-ray images were successfully...

Indirect-direct hybrid target experiments with the GEKKO XII laser

A new fusion capsule drive scheme was investigated. The capsule is illuminated by a low intensity thermal X ray pulse prior to the main drive pulse. This leads to a noticeable suppression of initial imprinting by the drive beam because of thermal smoothing in the preformed plasma. Of the several types of indirect-direct hybrid target, the authors investigated the hybrid effect for two types. One is a foam hybrid, in which the fuel capsule has a low density foam layer attached directly on its surface and where pulsed radiation generated from a thin high Z layer on the foam propagates through the foam, creating a preformed plasma. The other is an external hybrid, in which the capsule is illuminated by external X ray radiation generated using different beams from the capsule drive beams. The hybrid effect was demonstrated for both types by imposing an initial imprint on a planar target with an intensity modulated beam, and subsequent non-uniformity growth due to Rayleigh-Taylor instability was observed by means of face-on backlighting. The observed suppression due to the presence of the preformed plasma is interpreted by a cloudy day model for both hybrids. Capsule implosion experiments have also been started. The overall implosion dynamics observed is replicated by 1-D hydrocode simulations. Preliminary results from the implosion experiments are presented.

Laser‐imploded core structure observed by using two‐dimensional x‐ray imaging with 10‐ps temporal resolution

Core plasmas of laser‐imploded ICF targets were observed by using a 10‐ps temporally resolved two‐dimensional x‐ray imaging technique. A multi‐imaging x‐ray pinhole camera was coupled to an x‐ray streak camera, and two‐dimensional images were reconstructed by handling the streaked image data. Image distortion of the system was evaluated and nonuniformity in sensitivity was corrected. The spatial resolution was 15 μm and the observed photon energy was 2.2–4.9 keV. Structures in the x‐ray image of the core were found to be rapidly changing with 10‐ps time scale.

Infrared photoinduced alignment change for triphenylene-based columnar liquid crystals by using free electron laser

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.

Ultrafast two-dimensional x-ray imaging with x-ray streak cameras for laser fusion research (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 μm, 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.

Gelatin ablation wavelength dependency in the range of 5.6–6.7 μm using a mid-infrared Free Electron Laser

Abstract 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 λ = 6.45 µm, tuned to the amide-II band of protein. Gelatin ablation experiments have been carried out using a mid-infrared FEL within the waveband λ = 5.6–6.7 µm by changing the primary absorbers such as water (λ = 6.1 µm) and protein (λ = 6.45 µm). The gelatin with 80 wt% water was efficiently ablated by FEL irradiation with the waveband λ= ∼5.95–6.19 µm. On the other hand, using irradiation within λ = ∼6.4–6.6 µm, 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 ∼6.1 µm, not ∼6.45 µm, in order to cut soft tissue with a high water concentration at the expense of surface smoothness.© 2003 Elsevire Scienec B.V. All righst reserved.PACS: 42.62.Be

Penumbral imaging for measurement of the ablation density in laser-driven targets

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 μm 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 sim...

Cryogenic deuterium target experiments with the GEKKO XII, green laser system

A series of experiments were conducted using cryogenic deuterium targets to study fundamental physics and implosion dynamics with the GEKKO XII glass laser system [IEEE J. Quantum Electron. QE‐17, 1639 (1981)]. Preheat sources were found to be due to a shock wave and hot electrons. A new method to measure the fuel ρR using proton spectra was employed. Measured in detail were the implosion dynamics of cryogenic deuterium foam with a plastic ablator and a CH shell with a controlled pressure of deuterium gas targets. Under current experimental conditions sources of nonuniformity were discussed in terms of Rayleigh–Taylor instability.