Theory of terahertz generation in a slab of electro-optic material using an ultrashort laser pulse focused to a line

A theory that describes the optical-to-terahertz conversion of femtosecond laser pulses via optical rectification in a slab of an electro-optic material is developed. Two typical experimental situations-phase-matched regime (ZnTe excited with 780 nm optical pump) and non-phase-matched regime (LiNbO3 excited with 800 nm optical pump and GaAs excited with 1.56 mu m optical pump)-are considered. The theory accounts for the transverse size of the laser beam and allows us to explore the dependence of the conversion efficiency on laser focusing. We trace the temporal dynamics of the optical-to-terahertz conversion inside the slab and study the angular distribution of the terahertz emission from the slab. The optimal parameters (such as laser transverse size and crystal thickness) maximizing the terahertz yield for ZnTe and GaAs are calculated.