Tailoring Terahertz Pulses with Moving Fronts: Temporal Stretching and Time-Reversal

We demonstrate experimentally a strategy for using relativistic moving dielectric fronts to trigger and affect the generation of coherent terahertz (THz) pulses. Our emission mechanism draws energy from the photoexcitation of built-in static Schottky fields present at metal-semiconductor boundaries in a silicon-filled parallel plate waveguide (PPWG). Fronts tuned to sub-luminal velocity produce THz pulses whose electric field temporal profile displays a stretched plateau of quasi-dc character. Super-luminal fronts, on the other hand, provide access to front-induced interactions giving a clear signature of pulse time-reversal.