  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.
