We propose a new propagation formula for the Maxwell field in de Sitter space which exploits the conformal invariance of this field together with a conformal gauge condition. This formula allows to determine the classical electromagnetic field in the de Sitter space from given currents and initial data. It only uses the Green's function of the massless Minkowskian scalar field. This leads to drastic simplifications in practical calculations. We apply this formula to the classical problem of the two charges of opposite signs at rest at the North and South Poles of the de Sitter space.

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We report a photoconductive switch with GaNAsSb as active material for microwave switching application. The GaNAsSb layer was grown by molecular beam epitaxy in conjunction with a rf plasma-assisted nitrogen source and a valved antimony cracker source. The 0.5 μm thick GaNAsSb photoabsorption layer contains 3.5% of N and 9% of Sb. The switch exhibits pulsed response with full width at half maximum of 30 ps and photoresponse of up to 1.6 μm. In microwave switching application, the switch shows ON/OFF ratio of 11 dB at 1 GHz and response up to 15 GHz.