Efficient Cherenkov emission of broadband terahertz radiation from an ultrashort laser pulse in a sandwich structure with nonlinear core

Abstract

A scheme for efficient generation of broadband terahertz radiation by a femtosecond laser pulse propagating in a planar sandwichlike structure is proposed. The structure consists of a thin nonlinear core cladded with prisms made of a material with low terahertz absorption. The focused into a line laser pulse propagates in the core as a leaky or waveguide mode and emits Cherenkov wedge of terahertz waves in the cladding. We developed a theory that describes terahertz generation in such a structure and calculated spatial distribution of the generated terahertz field, its energy spectrum and optical-to-terahertz conversion efficiency. The developed theory predicts the conversion efficiency of up to several percent in a 1 cm long and 1 cm wide Si–LiNbO3–Si sandwich structure with a 20 μm thick nonlinear layer pumped by 8.5 μJ Ti:sapphire laser with pulse duration of 100 fs.