Generation of spectrally bright THz fields for nonlinear spectroscopy in LiNbO₃ slab waveguides

We use an intensity-modulated optical excitation to generate multicycle THz fields with high spectral brightness within a lithium niobate slab waveguide for compact nonlinear THz spectroscopy. Two methods for producing intensity-modulated optical pump pulses are experimentally evaluated. Multicycle THz pulses at 0.3 THz are generated with peak electric fields of 40 kV/cm and spectral bandwidths as narrow as 11%, with frequency tunability up to 0.1 THz. Despite moderate 2 mJ laser powers, the THz spectral amplitude is sufficient to conduct nonlinear two-dimensional THz spectroscopy of magnon dynamics in YFeO₃. With no free-space THz propagation, this method of multicycle THz generation, sample interaction, and near-field detection is ideal for nonlinear THz spectroscopy and signal processing in space-limited configurations.