Parametric Four-Photon Generation of Picosecond Light at High ConversionEfficiency

Parametric four-photon interaction in isotropic media was studied in the saturation range. Up to 10% of input laser energy could be converted into a broad frequency spectrum ranging from the ultraviolet to the infrared. Parameters which influence the conversion efficiency are discussed

Forming and confining of dipolar excitons by quantizing magnetic fields

We show that a magnetic field perpendicular to an AlGaAs/GaAs coupled quantum well efficiently traps dipolar excitons and leads to the stabilization of the excitonic formation and confinement in the illumination area. Hereby, the density of dipolar excitons is remarkably enhanced up to $\sim 10^{11} cm^{-2}$. By means of Landau level spectroscopy we study the density of excess holes in the illuminated region. Depending on the excitation power and the applied electric field, the hole density can be tuned over one order of magnitude up to $\sim 2.5$ $10^{11} cm^{-2}$ - a value comparable with typical carrier densities in modulation-doped structures.Comment: 4.3 Pages, 4 Figure

The wheat ω-gliadin genes: structure and EST analysis

A survey and analysis is made of all available ω-gliadin DNA sequences including ω-gliadin genes within a large genomic clone, previously reported gene sequences, and ESTs identified from the large wheat EST collection. A contiguous portion of the Gli-B3 locus is shown to contain two apparently active ω-gliadin genes, two pseudogenes, and four fragments of the 3′ portion of ω-gliadin sequences. Comparison of ω-gliadin sequences allows a phylogenetic picture of their relationships and genomes of origin. Results show three groupings of ω-gliadin active gene sequences assigned to each of the three hexaploid wheat genomes, and a fourth group thus far consisting of pseudogenes assigned to the A-genome. Analysis of ω-gliadin ESTs allows reconstruction of two full-length model sequences encoding the AREL- and ARQL-type proteins from the Gli-A3 and Gli-D3 loci, respectively. There is no DNA evidence of multiple active genes from these two loci. In contrast, ESTs allow identification of at least three to four distinct active genes at the Gli-B3 locus of some cultivars. Additional results include more information on the position of cysteines in some ω-gliadin genes and discussion of problems in studying the ω-gliadin gene family