 When the applied electric field is delivered by a femtosecond-pulse-width laser, the spectral bandwidth associated with such short pulses is very large.The mixing of different frequency components produces a beating polarization, which results in the emission of electromagnetic waves in the terahertz region.The EOR effect is somewhat similar to a classical electrodynamic emission of radiation by an accelerating/decelerating charge, except that here the charges are in a bound dipole form and the THz generation depends on the second order susceptibility of the nonlinear optical medium.