The dependence of the THz signal on the incidence angle [10, 12]. (a) THz intensity with different incidence angles is studied by rotating the water film. The THz signal is maximized when is 65°. The squares are the experimental results, and the red line is a simulated result from a dipole model. (b) Two THz waveforms obtained with opposite incident angles. The insets explain the observation with a contribution of the flipped dipole projection () of opposite incidence angles.