Abstract:
It has been shown that counterpropagating electromagnetic waves with different frequencies generate two lattices in a cubically nonlinear medium, one of which moves at a superluminal velocity. When weak radiation reflects from the superluminal lattice, the wavefront is quasi-conjugated with distortions owing to the Doppler frequency shift. These effects occur both in insulators with fast nonlinearity and in an electron-positron vacuum.
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