A double-Gaussian model and the Schmidt modes are found for the biphoton wave function characterizing spontaneous parametric down-conversion with the degenerate collinear phase-matching of the type I and with a pulsed pump. The obtained results are valid for all durations of the pump pulses, short, long and intermediately long.

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The gamma-ray blazar 1611+343 was observed with polarization VLBI mode at 5 GHz in February 1999. The total intensity (I) VLBI image of the source shows a core-jet structure. The jet bends eastward at ∼ 3 mas south of the core. Four components have been detected from results of fitting, with apparent speeds estimated at 6.7 ± 0.7, 2.5 ± 0.3, 4.5 ± 0.5 h −1 c for three jet components (taking H 0 = 100 h km s −1 Mpc −1 , q 0 = 0.5). The polarization (P ) VLBI image of 1611+343 displays the polarized configuration in the jet. The mechanism of the curved jet is discussed.