Spatiotemporal pulse shaping and nonlinear terahertz spectroscopy

• Applicant: Thomas Hornung
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2002 to 2005
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5395344

Novel 'spatiotemporal' femtosecond pulse shaping methods, recently developed in the group of Prof. Keith Nelson at MIT, promise an unprecedented degree of coherent optical control over terahertz-frequency lattice waves, called phononpolaritons, that move at ligth-like speeds through crystalline solids. My postdoctoral project in the Nelson group will have the following central aims. (i) Development of time-resolved nonlinear THz spectroscopy, a nascent field still awaiting its first demonstration, and application of the study of liquid-state molecular dynamics. THz pump-probe, photon echo, hole-burning, and other measurements will be carried out, using intense THz excitation pulses to drive molecular orientations and other motions and using time-delayed THz or visible pulses to monitor the responses. (ii) Study and coherent optical control of nonlinear lattice responses and collective structural change induced in crystalline solids by large-amplitude lattice vibrations. In ferroelectric crystals, including mixed ferroelectrics with nanometer-sized oriented domains, large vibrational amplitudes will move ions along the collective paths the they follow during switching to new domain orientations, that is, the paths that lead to collective lattice rearrangement. Nonlinear responses will reveal the anharmonic lattice potentials that mediate rearrangement, and optical control over lattice structure will be attempted. Generation of polaritonic shock waves and soliton waves, predicted theoretically to arise at large amplitudes, will be attempted as well. An allied objective is practical application of the pulse shaping and coherent control methods for THz-bandwidth polaritonic signal processing in patterned materials.

• DFG Programme: Research Fellowships