Generation of 0.7 mJ multicycle 15 THz radiation by phase-matched optical rectification in lithium niobate.

We demonstrate efficient multicycle terahertz pulse generation at 14.6 THz from large-area lithium niobate crystals by using high-energy (up to 2 J) femtosecond Ti:sapphire laser pulses. Such terahertz radiation is produced by phase-matched optical rectification in lithium niobate. Experimentally, we achieve maximal terahertz energy of 0.71 mJ with conversion efficiency of $\sim$0.04%. We also find that the effective interaction length for optimal terahertz conversion is fundamentally limited by terahertz absorption, laser pulse stretching by material dispersion, and terahertz-induced nonlinear cascading effects on the driving laser pulse.