Highly efficient multicycle terahertz generation in PPLN

We experimentally measure percent-level optical-to-multi-cycle terahertz conversion efficiencies by injecting a home-made wavelength- and duration-tunable two-line laser into periodically poled lithium niobate. We study the efficiency vs. the input laser peak fluence, pulse duration, crystal length and poling period at cryogenic temperature. Our work is a significant step towards high energy terahertz pulses for linear electron acceleration.