We analyze and simulate a mechanism for generating directed rf radiation when a laser pulse train forms a plasma filament in air. The frequency of the radiation is determined by the laser pulse separation.

499Figure 6(A) illustrates the structure of pyrolytic TiB2 as deposited. The (1 10) plane, which includes both boron atoms as well as the four titanium atoms a t the extreme corners of the hexagonal unit cell, was parallel to the plane of deposition. The atomic arrangement of alternating layers of titanium and boron atoms perpendicular to the plane of dcposition as well as the TiBz unit cell are indicated. The interatomic distances were based on the data of Kiessling.2(0) Figure 6(B) illustrates the array of atoms in the plane parallel to the plane of deposition and indicates the anisotropy within this plane. Since two electrical paths, one involving Ti-B bonds only and the other involving B-B bonds, are possible, a determination of the electrical resistivity in each of the anisotropic directions should indicate the strength and importance of boron-to-boron bonding in such compounds.A number of phosphate glasses with unusually high vanadium content were studied with respect to some of their electrical properties.It was found that 75 to 85 wt% V205 could be reacted with various metaphosphates (Ba, Pb, Li, Na, Cd, V, and K) resulting in good-quality reproducible glasses in 500-g melts. The electrical resistance of these glasses appeared to be particularly dependent on their thermal history below the liquidus but above the transformation range. A large change in specific resistance resulted when vitreous specimens were heattreated to produce varying amounts of devitrification. For a specimen containing potassium metaphosphate, resistivity was reduced from about lo3 to 10 ohm-cm.

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