A new nanophase-separated structure with parallel double periodicity has been identified for an undecablock terpolymer in bulk. The polymer includes two long poly(2-vinypyridine) (P) chains on each end, with five short polyisoprene (I) and four short polystyrene (S) chains at the center. This polymer exhibits a hierarchical lamellar structure with two crystallographic periods: 88 nm and 16 nm. The 88 nm period includes one thick P lamella and five thin I-S-I-S-I lamellae, of extremely high orientation.

A two-component multiblock copolymer with undecablockstwo of them on both chain ends are long and nine of them are shortswas successfully prepared by anionic polymerization using the sixstep sequential monomer addition technique. Polymer components are polystyrene (S) and polyisoprene (I), its total molecular weight is 275K, and the overall S/I volume ratio is 0.70/0.30. Microphase-separated structure of the copolymer was observed by transmission electron microscopy and small-angle X-ray scattering, and it was confirmed that the copolymer forms a complex lamellar structure; its long period is 45 nm, which is composed of one thick lamellar domain formed by long polystyrene chains and I-S-I three thin lamellar domains, the length of the short period for I-S lamellae being about one-third of the longer period. This fact shows short block chains at the center favorably adopt a loop conformation over a bridge one. This unique lamellar structure having two length scales must be the first experimentally observed simple hierarchical structure for the block copolymer where the component polymers are connected by covalent bonds.

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We report the first observation of amplification of spontaneous emission on the Lyman-a transition of hydrogenlike lithium ions by optical-field-induced ionization. Using a subpicosecond KrF laser (0.5 ps, 50 mJ) focused at 10 17 W/cm 2 , singly ionized lithium ions have been further ionized to fully stripped states, resulting in the population inversion with respect to the ground state of the hydrogenic ions. A small signal gain coefficient of 20 cm _1 was obtained.PACS numbers: 32.80. Rm, 42.55.Vc, 52.50.Jm Recent research in x-ray lasers has focused on the development of more efficient and shorter wavelength lasers which can be pumped by a compact driver. Present x-ray layers [1,2] require large scale and very expensive drivers to heat a plasma medium to a desired ionization state by collisional excitation. Recently, Burnett and co-workers [3,4], Amendt, Eder, and Wilks [5], and Eder, Amendt, and Wilks [6] have proposed a new scheme for an x-ray laser based on an optical-field-induced ionization (OFI). In this scheme, an ultrashort high-intensity laser produces a plasma consisting of fully stripped ions and cold free electrons on a time scale much shorter than the recombination time. In such a plasma, a rapid recombination cascade of the electrons could lead to a population inversion because of a sufficiently low electron temperature of the plasma. X-ray lasing by OFI, however, has not yet been demonstrated.The use of OFI for the production of an x-ray laser plasma medium introduces some favorable characteristics. First, it is possible to produce population inversions with respect to the ground state of an ion [7,8], leading to a transition to much shorter wavelength compared to relevant transitions. The transition between n=2 and 1 in H-like ions has a photon energy 5 times as large as the transition between n=3 and 2 state. Second, the use of ultrashort pulses requires a lower pump energy, compared with conventional x-ray laser schemes. The recent progress in the technology of ultrashort laser pulses would make it possible to realize table top laser drivers for OFI x-ray lasers.This Letter reports the first observation of the amplification of spontaneous emission on the Lyman-a transition (13.5 nm) in H-like Li ions, using a novel optical-fieldinduced ionization scheme. A very large small-signal gain coefficient of 20 cm ~l was obtained from the exponential growth of the 13.5 nm line intensity against the linear increase of the gain length. The anisotropy of the amplified spontaneous emission was also observed by comparing with the relative intensities along on-axis and off-axis directions.Our method described in this Letter is a unique modification of the original OFI scheme proposed previously [3][4][5][6]. In our scheme, singly ionized lithium ions which are initially prepared by a nanosecond KrF excimer laser are further ionized to a fully stripped state by a subpicosecond high-intensity KrF laser. This modified scheme provides some advantages for the production of cold electrons and for pump beam foc...