Caustics of a light beam passing through a time-varying dielectric wedge

Abstract A caustic of cusp type in space-time is found to arise in a laser beam deflected by a wedge with time-varying refractive index. Asymptotic formulae describing the wave field under the assumption that the refractive index varies slowly compared with the oscillations of the light wave are given. The intensity of the wave field at the cusp point can be, say, 103 times greater than the initial one. The temporal variation of the field at the cusp gives rise to an ultrashort pulse. The lengths of these pulses can be 105 times less than the characteristic time of modulation of the refractive index, i.e., of subpicosecond range.