Seminar | ||||||||||
| Chemistry | ||||||||||
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It has recently become possible to generate single-cycle or multiple-cycle electromagnetic fields in the 1-THz frequency range with electric field strengths in the 0.1-10 MV/cm range under various conditions. This is sufficient to induce nonlinear responses in many systems including inorganic and organic crystalline solids and molecular liquids and gases. In some systems the THz field resonantly drives low-frequency electronic, lattice vibrational, or molecular rotational modes. In others, the responses are driven through nonresonant light-matter interactions including above-threshold ionization and classical acceleration of electrons to multi-eV energies. The results enable spectroscopy and control of newly accessible nonequilibrium states. High-field THz generation and interactions with different samples will be reviewed, and then two systems will be discussed in greater detail. Results from the first THz-induced phase transition, the insulator-metal transition in the prototype correlated electron system vanadium dioxide, will be presented. The collective electronic transition was monitored using THz and optical probe fields, and the coupled structural phase transition was observed through femtosecond x-ray diffraction off the crystal lattice. Finally, THz excitation of molecular rotational coherences and populations, including unique examples of field-free molecular orientation, multiple-transition coherent control, two-dimensional spectroscopy, and super(duper)radiance will be discussed. | ||||||||||
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