We theoretically and experimentally investigate the fully evolution of Gouy phase in a longitudinal terahertz wave during the entire focal region. By comparing the pulses shape and orientation before and after the focus, we find that the complete phase shift for the longitudinal field components is same to that of the transverse field components, with the value of π. The only different between them is their phase difference π/2. Additionally, it is found that the intensity and pulse orientation of longitudinal terahertz wave can be controlled effectively by a longitudinal static electric field, by changing its voltage and direction. The physical origin is that the external static longitudinal field added to the electrostatic field created by the initial laser pondermotive force, which changes the intensity and phase of emitted radial terahertz wave and then affected its longitudinal field component. This phase measure and control of longitudinal electromagnetic fields have important implications for the near-field optical microscopy and super-resolution imaging.
© 2016 Optical Society of AmericaPDF Article