Frequency tunable $THz$-generation in periodically poled lithium niobate crystal

A simple method for the generation of quasi-monochromatic tunable terahertz ($THz$) pulses via optical rectification of femtosecond laser pulses in periodically poled lithium niobate (PPLN) crystal was proposed. It is shown that when the incidence angle on the crystal of the optical beam changes in the range of $-50^{\circ}\ $ to $+50^{\circ}\ $, the central frequency of the generated $THz$ radiation varies from $\sim0.77\ $ to $\sim0.93 \ THz$ and the direction of $THz$-radiation changes in the range of $-10^{\circ}\ $ to $+10^{\circ}\ $. Thus, an appropriate choice of parameters PPLN and the angle of incidence of the laser beam is possible to obtain quasi-monochromatic $THz$-radiation tunable over a sufficiently wide frequency range.