Observation of "Frozen-Phase" Propagation of THz Pulses in a Dispersive Optical System

Dispersion occurs naturally in many wave systems. So far, a variety of techniques have been proposed and demonstrated to compensate the second-order (group-velocity) dispersion, such as dispersion management and nonlinear soliton formation, yet it is commonly believed that the first-order dispersion (FOD) is less amenable and cannot be eliminated. In this work, it is shown that a phase-invariant propagation of THz pulses, namely the "frozen-phase" propagation, can be realized by a complete cancellation of the FOD, achieved by implementing a synchronized THz moving source with a locked initial phase. The dynamic generation and propagation process of the THz pulses is examined directly by a time-resolved imaging system. To the best of authors' knowledge, this represents the first demonstration of the "frozen-phase" propagation of a light pulse in dispersive optical systems.