  Using a canonical pump-probe experimental technique, we studied the terahertz
(THz) waves generation and detection via optical rectification and mixing in
Czochralski-grown periodically poled Mg:Y:LiNbO3 (PPLN) crystals. THz waves
with frequencies at 1.37 THz and 0.68 THz as well as 1.8 THz were obtained for
PPLN with nonlinear grating periods of 0.03 and 0.06 mm, respectively. A
general theoretical model was developed by considering the dispersion and
damping of low frequency phonon-polariton mode. Our results show that THz waves
are generated in forward and backward directions via pumping pulse
rectification. The generated THz waves depend on the spectral shape of the
laser pulses, quasi-phase mismatches and dispersion characteristics of a
crystal.
