Broadband highly efficient source of collimated terahertz radiation driven by an ultrafast optical oscillator.

We demonstrate experimentally an efficient terahertz emitter that consists of a 20 µm thick layer of LiNbO clamped between a fused silica substrate and a Si semicone. A focused laser beam from an ultrafast optical oscillator propagates in the LiNbO layer and emits a Cherenkov cone of terahertz radiation to the Si semicone. The radiation is totally internally reflected by the semicone's convex surface and escapes the semicone through its base as a collimated beam.

Light scattering at a temporal boundary in a Lorentz medium.

Temporal discontinuity in the permittivity of a nondispersive dielectric (temporal boundary) is a conventional model for considering electromagnetic phenomena in dynamic materials and metamaterials. Here we apply a more general model of a Lorentz medium with the rapidly changing density of its structural elements (oscillators) or their resonant frequency to determine the realms of applicability of the conventional temporal boundary model. We demonstrate the dependence of the continuity conditions and the energy relations at a temporal boundary on the nonstationarity mechanism and the ratio between the rate of nonstationarity and the characteristic frequencies in the system.

Long propagating velocity-controlled Einstein's mirror for terahertz light conversion.

We show that Einstein's relativistic mirror with long (hundreds of µm) propagation distance and controllable propagation velocity can be implemented in the form of a dense free carrier front generated by multiphoton absorption of tilted-pulse-front femtosecond laser pulses in a dielectric or semiconductor medium. The velocity control is achieved by varying the pulse front tilt angle. Simulations demonstrate that such fronts can serve as efficient Doppler-type converters of terahertz pulses.