Terahertz polaritonics

Mixed polar lattice vibrational and electromagnetic modes, called phonon-polaritons, which propagate at light-like speeds through their host crystals are unique and powerful sources of THz radiation. One way to excite them is by nonresonant impulsive stimulated Raman scattering using femtosecond laser pulses. New techniques in spatiotemporal imaging and spatiotemporal and spatial-only femtosecond pulse shaping and structuring of crystal materials have been developed to enable versatile spatiotemporal coherent control over the propagating phonon-polaritons and thereby over the associated THz fields. Achieving control over propagating coherent responses places new demands on both the excitation and probing processes. Versatile spatiotemporal control over coherent, multiplexed, single-cycle or multicycle THz waves is demonstrated through programmable phased-array generation and traveling wave amplification using spatiotemporally shaped ultrafast optical excitation fields. Movies of THz signal propagation through bulk or patterned samples including solid-state waveguides and resonators are viewed directly through spatiotemporal imaging.