Generation of multicycle terahertz phonon-polariton waves in a planar waveguide by tilted optical pulse fronts

We demonstrate generation of frequency-tunable, multicycle terahertz phonon-polariton waves in a LiNbO(3) slab waveguide. Because the waveguide modes show considerable phase-velocity dispersion, we are able to enhance frequency-selected narrowband terahertz waves by using femtosecond optical pulses whose intensity fronts are tilted at angles that meet the appropriate noncollinear phase-matching conditions. The pump light is spread across a large area of the crystalline waveguide within which coherent terahertz wave generation occurs, averting material damage, while yielding peak-to-peak terahertz field amplitudes in the waveguide of 50 kV/cm.