Pulsed THz radiation under ultrafast optical discharge of vacuum photodiode.

In this paper, we first present an experimental demonstration of terahertz radiation pulse generation with energy up to 5 pJ under the electron emission during ultrafast optical discharge of a vacuum photodiode. We use a femtosecond optical excitation of metallic copper photocathode for the generation of ultrashort electron bunch and up to 45 kV/cm external electric field for the photo-emitted electron acceleration. Measurements of terahertz pulses energy as a function of emitted charge density, incidence angle of optical radiation and applied electric field have been provided.

Narrow intensity range optical anisotropy in air induced by a femtosecond laser breakdown.

In this paper, we study the optical anisotropy induced by femtosecond laser radiation in air during an optical breakdown. Using a transverse pump-probe technique, we demonstrate that this anisotropy appears in a narrow range of pump intensities, which are close to the optical breakdown threshold in air and lead to a phase shift of probe radiation, polarized collinear to the pump. The intensity range where an induced intense anisotropy occurs makes it possible to estimate the magnitude of the 5th-order Kerr nonlinear refractive index component in air.