Efficient Cherenkov-type optical-to-terahertz converter with terahertz beam combining

Abstract

A nonlinear structure for efficient Cherenkov-type terahertz emission from ultrashort laser pulses is proposed, modeled, and experimentally demonstrated. The structure comprises a thin (a few tens of micrometers thick) layer of lithium niobate sandwiched between two silicon prisms. A focused-to-a-line laser pulse propagates in the layer and generates a Cherenkov wedge of terahertz radiation in the prisms. The radiation experiences total internal reflection in the prisms and emerges into free space as two adjacent beams collinear to the pump laser beam. The structure can generate a centimeter-wide terahertz beam with high transverse uniformity and a flat frequency spectrum. An optical-to-terahertz conversion efficiency as high as 0.35% is achieved with 10-µJ laser pulses. It can be further enhanced by reducing the thickness of the lithium niobate layer.