2) Broadband / intense time-domain THz spectroscopy
We have built up a broadband time-domain THz spectroscopy ranging from 0.1 to 10-200 THz using photoconducting semiconductor antennas or nonlinear organic crystals with ultrashort laser pulses (≤10 fs). We have also generated intense THz pulses using an Mg-doped LiNbO3 single crystal excited by laser pulses having a tilted pulse front. Using these THz techniques, dynamics of free carriers due to surface metallic states, electron-phonon couplings and lattice vibrational modes relevant to photochemical reactions and structural phase transitions can be revealed.
- I. Katayama, H. Aoki, J. Takeda, H. Shimosato, M. Ashida, R. Kinjo, I. Kawayama, M. Tonouchi, M. Nagai and K. Tanaka, "Ferroelectric Soft Mode in a SrTiO3 Thin-Film Impulsively Driven to the Anharmonic Regime Using Intense Picosecond Terahertz Pulses", Phys. Rev. Lett., 108, 097401: pp. 1-5(2012).
- I. Katayama, R. Akai, M. Bito, H. Shimosato, K. Miyamoto, H. Ito and M. Ashida, "Ultrabroadband Terahertz Generation Using 4-N,N-Dimethylamino-4'-N'-Methyl-Stilbazolium Tosylate Single Crystals", Appl. Phys. Lett., 97, 021105 (2010).