The characteristic energy of many fundamental processes in molecules and condensed matter lies in the terahertz (THz) frequency range; examples include biologically important collective vibrations of proteins, crystal lattice resonance oscillations, electron transitions in semiconductor nanostructures, and Cooper pairs formation in superconductors. Nonlinear THz spectroscopy can provide new information about these processes. However, very few studies on nonlinear THz spectroscopy have been published to date, in contrast to the large number of studies on nonlinear spectroscopy in the visible range. One of the main reasons limiting the development of nonlinear THz spectroscopy is the lack of available sources of high-power THz radiation. Many previous studies on THz nonlinear spectroscopy have been performed using accelerator-based sources. However, these sources present the typical drawbacks associated with large-scale facilities. A few laser-driven table-top THz generation techniques have been proposed and realized. Usually the power of the THz waves delivered this way is relatively weak. Since 2003, I have actively worked on the development of the tilted-pulse-front pumping THz generation scheme originally proposed by J. Hebling in 2002. This method allows to efficiently scaling up the energy of single-cycle THz pulse. Very recently, in two joint experiments with the host group, I have demonstrated the generation of the highest energy single-cycle THz pulses to date produced with a laser-based approach. As a continuation of this preliminary demonstration, during this project I plan to exploit the unique high-power laser facility of the host group and develop a permanent laser-driven platform for obtaining high power ultrashort THz pulses with variable parameters for performing nonlinear spectroscopy in the THz frequency range. In particular, I intend to study THz nonlinear properties of new metamaterials and nonlinear interaction of THz waves and laser filaments.
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