Large-area periodically-poled lithium niobate wafer stacks optimized for high-energy narrowband terahertz generation

Mosley, Connor D. W. and Lake, Daniel S. and Graham, Darren M. and Jamison, Steven P. and Appleby, Robert B. and Burt, Graeme and Hibberd, Morgan T. (2023) Large-area periodically-poled lithium niobate wafer stacks optimized for high-energy narrowband terahertz generation. Optics Express, 31 (3). pp. 4041-4054. ISSN 1094-4087

Abstract

Periodically-poled lithium niobate (PPLN) sources consisting of custom-built stacks of large-area wafers provide a unique opportunity to systematically study the multi-cycle terahertz (THz) generation mechanism as they are assembled layer-by-layer. Here we investigate and optimize the THz emission from PPLN wafer stacks as a function of wafer number, pump fluence, pulse duration and chirp, wafer separation, and pump focusing. Using 135 µm-thick, 2"-diameter wafers we generate high-energy, narrowband THz pulses with central frequencies up to 0.39 THz, directly suitable for THz-driven particle acceleration applications. We explore the multi-cycle pulse build-up with increasing wafer numbers using electro-optic sampling measurements, achieving THz conversion efficiencies up to 0.17%, while demonstrating unique control over the pulse length and bandwidth these sources offer. Guided by simulations, observed frequency-dependence on both stack-mounting and pump focusing conditions have been attributed to inter-wafer etalon and Gouy phase-shifts respectively, revealing subtle features that are critical to the understanding and performance of PPLN wafer-stack sources for optimal narrowband THz generation.