Nobukatsu Nemoto

Foam materials for cryogenic targets of fast ignition realization experiment (FIREX)

Development of foam materials for cryogenically cooled fuel targets is described in this paper. The fabrication development was initiated as a part of the fast ignition realization experiment (FIREX) project at the ILE, Osaka University under a bilateral collaboration between Osaka University and National Institute for Fusion Science (NIFS). For the first stage of FIREX (FIREX-I), a foam cryogenic target was designed in which low-density foam shells with a conical light guide will be fuelled through a narrow pipe and will be cooled down to the cryogenic temperature. Acrylic polymer, resorcinol–formaldehyde (RF) resin, poly(4-methyl-1-pentene) (PMP), and polystyrene-based crosslinking polymer have been investigated as supporting materials for cryogenic fuel. The properties of the material and the present status of the material development are summarized.

Fabrication of aerogel capsule, bromine-doped capsule, and modified gold cone in modified target for the Fast Ignition Realization Experiment (FIREX) Project

The development of target fabrication for the Fast Ignition Realization EXperiment (FIREX) Project is described in this paper. For the first stage of the FIREX Project (FIREX-I), the previously designed target has been modified by using a bromine-doped ablator and coating the inner gold cone with a low-density material. A high-quality bromine-doped capsule without vacuoles was fabricated from bromine-doped deuterated polystyrene. The gold surface was coated with a low-density material by electrochemical plating. For the cryogenic fuel target, a brand new type of aerogel material, phloroglucinol/formaldehyde (PF), was investigated and encapsulated to meet the specifications of 500 µm diameter and 20 µm thickness, with 30 nm nanopores. Polystyrene-based low-density materials were investigated and the relationship between the crosslinker content and the nanopore structure was observed.

Ab initio MO investigations of molecular structures in the ground and first excited states of heterocyclic pyridinium betaine

Abstract The molecular structure in the first excited state of the simplest heteorcyclic pyridinium betaine, (1-pyridinio)benzimidazolate, was investigated through ab initio molecular orbital calculations. The central C-N bond shortens to a nearly double bond character in contrast to the case for the ground state, and the pyridinium ring takes a para-quinoid-like structure. The dipole moment direction in the excited state and the ground state are anti-parallel, and the benzimidazole ring acts as an electron-donating group and the pyridinium ring acts as an electron-withdrawing group, and the first excited state is characterized by an intramolecular charge transfer state. Based on these characteristic features of heterocyclic pyridinium betaines, a new concept for manipulating the molecular dipole moment and molecular first-order hyperpolarizability is proposed.

A new class of second-order non-linear optical material: stilbazolium benzimidazolate derived from alkylsulfonyl substituted stilbazole

A novel stilbazolium benzimidazolate derivative,i.e. 2-(4-{2-[4-(octylsulfonyl)phenyl]ethenyl}pyridinio)benzimidazolate 4a, was prepared by the quaternization reaction of 4-{2-[4-(octylsulfonyl)phenyl]ethenyl}pyridine with 2-chlorobenzimidazole, followed by deprotonation with aqueous ammonia. Poly(methyl methacrylate) (PMMA) thin films containing 10 or 20 mass% of 4a were obtained by spin-coating from their THF solutions on an ordinary cover glass substrate. Second-harmonic generation (SHG) measurements of the obtained thin films were carried out by the Maker fringe method using a Q-switched Nd:YAG laser (1064 nm) as an exciting beam after corona-poling. A poled PMMA film containing 10 or 20 mass% of 4a exhibited a second-order non-linear optical (NLO) coefficient, d33 , of 7.6 or 11 pm V–1 , respectively, which was much larger than the d33 value of a PMMA thin film containing 10 mass% of 2-[4-(2-phenylethenyl)pyridinio]benzimidazolate 4c (d33 1.6 pm V–1) or 2-{4-[2-(4-octyloxyphenyl)ethenyl]pyridinio}benzimidazolate 4d (d33 0.51 pm V–1). There were no significant differences in linear absorption properties of PMMA films containing 4a, 4c or 4d. The introduction of an octylsulfonyl group at the 4′-position of the stilbazole moiety increases the second-order NLO coefficient.

All Optically Induced χ(2)Structures and Their Optical Anisotropy in Betaine Dispersed in Polymer Matrix

This paper is concerned with the noncentrosymmetric alignment of betaine molecules dispersed in a polymeric matrix by an all-optical poling process. Two types of betaine molecules were used: one is betaine-azo with an azobenzene moiety in the molecule and the other is betaine-C8 without an azobenzene moiety in the molecule. The effect of the azobenzene moiety in the molecule on the optical poling efficiency, the formation of χ(2) structure, and its thermal stability was studied. Optical anisotropy of the χ(2) tensor components formed in the matrix in the writing process with linearly polarized beams was evaluated by rotating a sample film or rotating the polarization direction of the fundamental reading beam.

Novel polyamides for second‐order nonlinear optics with side‐chain azo‐NLO‐phores

This article describes the syntheses and second-order nonlinear optical (NLO) properties of a novel type of polyamides with side-chain azo-NLO-phores. Two kinds of polyamides were prepared by condensation polymerization using 3-{N-methyl-4-[(4-methylsulfonylphenyl)azo]anilino]-1-propyl 3,5-diaminobenzoate (DA1) and 5-(3-{4-[4-(N,N-dimethylamino)phenylazo]phenyl}sulfonylpropyl)oxyisophthalic acid (IA1) or 5-(3-{N-methyl-4-[(4-methylsulfonylphenyl)azo]anilino}-1-propyl)oxyisophthalic acid (IA2). In the side chain of polyamide P3, which was obtained from DA1 and IA1, electron-donating and electron-withdrawing groups of the NLO-phores were alternatingly attached. In the side chain of polyamide P4, which was obtained from DA1 and IA2, electron-donating groups of all side-chain NLO-phores were attached to their backbone. The obtained polyamides exhibit relatively good solubility in common organic solvents and provide optical-quality films upon spin-coating. The second-harmonic generation (SHG) measurements of the obtained polyamides were carried out by the Maker fringe method using a Q-switched Nd: YAG laser as an exciting beam after corona-poling at various temperatures, indicating that P3 and P4 exhibit an optimum second-order NLO coefficient, d 33 , of 8.7 and 16.5 pm/V, respectively.

Novel optically transparent polyesters containing a high density of second-order non-linear optically active chromophores

The syntheses and second-order non-linear optical (NLO) properties of novel types of optically transparent polyesters containing a high density of second-order NLO-active chromophores are described. The chromophores used in this study contained either a perfluorooctyl- or an octyl-sulfonyl moiety as the electron-withdrawing group at the π-conjugating sites. The polyesters are prepared by condensation polymerization between isophthalic acid derivatives and 2-[N-(2-hydroxyethyl)-4-(perfluorooctylsulfonyl)anilino]ethanol by the use of triphenylphosphine and diethyl azodicarboxylate as the condensation reagents. The amorphous polyesters obtained, the optical transparency of which was down to 390 nm, exhibited good solubility in common organic solvents and provided optical-quality films by spin-coating. In addition, second-harmonic generation (SHG) measurements of spin-coated films of the polyesters were carried out by the Maker fringe method using a Q-switched Nd : YAG laser as the exciting beam after poling treatment. One of the polyesters, which was prepared from 5-{2-[N-methyl-4-(perfluorooctylsulfonyl)anilino]ethoxy}isophthalic acid and 2-[N-(2-hydroxyethyl)-4-(perfluorooctylsulfonyl)anilino]ethanol, exhibited the desired optical-transparency and a second-order NLO coefficient, d33, of 3.0 pm V–1.

Polystyrene based foam materials for cryogenic targets of fast ignition realization experiment (FIREX)

Abstract This paper deals with the development of materials without volume change in the formation of uniform low density foam capsules with fine structures. Two monomers, i.e., 5-(4-vinylbenzyl)oxymethyl-5-methyl-1,3-dioxane-2-thione (M1) and 4-vinylphenyloxirane (M2), were prepared as the comonomers polymerized with styrene. Polystyrene-based copolymers using styrene and M1 or M2 were prepared by free radical copolymerization using azobis(isobutyronitrile) (AIBN) as an initiator. The solutions of the obtained polystyrene-based copolymers in benzene/dichloromethane mixture or 4-chlorotoluene were gelated by the addition of a cationic initiator, which caused cross-linking via ring-opening polymerization of the pendant cyclic moieties. The gel was transformed into an aerogel by exchanging solvent to 2-propanol, and removal of 2-propanol using supercritical CO2. SEM images of a cross sectional view of the aerogel indicated that sub-micrometer voids were distributed randomly, and most of parts look filled bulk morphology. The density of the gel obtained from the present polystyrene-based copolymers was estimated to be 200 mg/cm3, which implies existence of vacancies without observation in the SEM image, suggesting the extremely fine cell structure.

A new class of second-order non-linear optical material:stilbazolium benzimidazolate covalently bound to polymer backbone

This paper describes the first example of the preparation of stilbazolium benzimidazolate covalently bound to polymer backbone using a novel methacrylate monomer, 2-{4-[2-(4-methacryloyloxyphenyl)ethenyl]pyridinio}benzimidazolate. A free radical copolymerization of 2-{4-[2-(4-methacryloyloxyphenyl)ethenyl]pyridinio}benzimidazolate (1 equiv.) with butyl methacrylate (6 equiv.) provided a methacrylate polymer containing 1.7 mol% of betaine units. The resulting polymer exhibited a glass transition temperature of 30 °C. The number-average (M n ) and weight-average (M w ) molecular masses were 36 900 and 79 300, respectively, estimated by GPC measurement. The second-order non-linear optical property of the obtained polymer was investigated by second-harmonic generation (SHG) measurements applying the Maker fringe method using a Q-switched Nd:YAG laser (1064 nm) as an exciting beam after corona-poling, indicating that the d 33 value of the resulting copolymer was 5.1 pm V -1 .

Novel concept for non-destructive readout method for photochromic rewriteable memory devices

Abstract A new concept for a non-destructive readout method for a photochromic rewriteable device is proposed based on a solvatochromic dye-linked photochromic dye system. From the theoretical molecular orbital calculations for the model compound, it was shown that the UV-Vis absorption band of the solvatochromic dye unit is sensitive to the conformation of the nearby photochromic unit. These calculations indicate that light corresponding to the UV-Vis absorption band of the solvatochromic dye unit can be used as the non-destructive readout light, since light in this region is found inactive to irradiation for achieving the photochromic reaction of the photochromic dye unit.