High Efficiency Terahertz Generation in a Multi-Stage System

TL;DR

This paper presents a multi-stage, laser-driven system for efficient narrowband terahertz generation in PPLN, achieving high conversion efficiency by recycling pump pulses and optimizing out-coupling, with detailed 2-D numerical modeling.

Contribution

It introduces a novel multi-stage architecture with pulse recycling and out-coupling, significantly enhancing terahertz generation efficiency compared to previous methods.

Findings

Achieved 1.6% total conversion efficiency at 0.3 THz

Predicted 17.6 mJ terahertz pulse with a 1.1 J pump laser

Each stage has over 0.8% efficiency with >93% out-coupling

Abstract

We describe a robust system for laser-driven narrowband terahertz generation with high conversion efficiency in periodically poled Lithium Niobate (PPLN). In the multi-stage terahertz generation system, the pump pulse is recycled after each PPLN stage for further terahertz generation. By out-coupling the terahertz radiation generated in each stage, extra absorption is circumvented and effective interaction length is increased. The separation of the terahertz and optical pulses at each stage is accomplished by an appropriately designed out-coupler. To evaluate the proposed architecture, the governing 2-D coupled wave equations in a cylindrically symmetric geometry are numerically solved using the finite difference method. Compared to the 1-D calculation which cannot capture the self-focusing and diffraction effects, our 2-D numerical method captures the effects of difference frequency generation, self-phase modulation, self-focusing, beam diffraction, dispersion, and terahertz absorption. We found that the terahertz generation efficiency can be greatly enhanced by compensating the dispersion of the pump pulse after each stage. With a two-stage system, we predict the generation of a $17.6$ mJ terahertz pulse with total conversion efficiency $\eta_{\text{total}}=1.6\%$ at $0.3$ THz using a 1.1 J pump laser with a two-line spectrum centered at 1 $\mu$m. The generation efficiency of each stage is above $0.8\%$ with the out-coupling efficiencies above $93.0\%$.