1. Nonlinearity in terahertz photon physics Masaya NAGAI Dep. Physics, Kyoto Univ. Janan PRESTO, JST, Japan June 15, 2010 APSE2010 Osaka, Japan

2. Colleague M. Jewariya, H. Hirori, K. Tanaka (Kyoto Univ.) I. Ichikawa, H. Ohtake, T. Sugiura, Y. Uehara (Aishin seiki) I. Katayama, H. Aoki, J. Takeda (Yokohama National Univ.) H. Shimosato, M. Ashida, R. Kinjo, I. Kawayama, M. Tonouchi (Osaka Univ.)

3. Outlines Intense THz field governs material properties non-collinear optical rectification with LiNbO 3 nonlinear spectroscopy in THz frequency region Vibrational mode in amino-acid microcrystal and SrTiO 3 e-h system in semiconductors Orientational motions in water Summary

4. Material Science in THz region Plasma motion 0.1nm1nm 1  m 1mm1m10nm100nm 10  m100  m 10mm100mm visble X  線 Intramolecular vibration Electric transition MIR  1  2  X-ray difraction microwave NIRUV X-ray  線 Orientational motion FIR  1  2 Intermolecular vibration Soft mode in dielectric material Superconductor gap …..

5. rot H = J cond + 4  D c  t Electronics (LCR, diode, etc) Photonics (transition between quantum levels) Typical timescale of damping  in solids is ps. Intense monocycle THz pulse can be assume as   i           i   ne 2 /m   Impulsive force with lowest center frequency as intense quasi-DC field ps timescale of damping  in materials

6. Intense THz pulse generation with tilted pulsefront excitation Tilted pulsefront Excitation pulse THz pulse EO crystal (Mg: LiNbO 3 ) Review: Hebling et al. J. Opt. Soc. Am. B 25, B6 (2008) 10  J v gr cos  = v THz

7. Intense THz pulse in Kyoto Univ. Output power 0.6  J Maximum filed 249 kV/cm Jewariya, MN, et al., JOSAB 26, A101 (2009).

8. Cascaded  (2) process enhances generation efficiency MN et al. Opt. Express, 17 11543 (2009). IMRA AMERICA FCPA  Jewel D1000 Wavelength: 1045nm Output power: 1W 10  J Repetition: 100kHz Duration: 600fs Excitation pulse Phase modulation Optical rectification THz pulse EO crystal

9. Large amplitude vibration driven with intense THz pulse Vibrational potential has anharmonicity, and large-amplitude vibrational motions (climbing higher excited levels) brings in dissociation, which is decisive for chemical reaction and phase transition. Using intense THz pulse resonant for vibrational modes, we can coherently drive large amplitude vibrational motions

10. Nonlinear medium: L-Arginine L-Arginine: amino-acid molecules L-Arginine microcrystal has the intermolecular vibration mode at 1 THz. Population kBTkBT Jewariya, MN, Tanaka, submitted

11. Time profile of Electric pulse passed through the arginine pellet X1/2 Jewariya, MN, Tanaka, submitted

12. Ladder climbing in anharmonic potential Above 10 steps Ladder climbing Large E(  ) small E(  ) Jewariya, MN, Tanaka, submitted

13. Coherent processes in several levels system    E 0 /h=1 P=Tr[  ]  nn  n-1 n-1  n+1 n+1  n+2 n+2 3 kV/cm 25 kV/cm 100 kV/cm n-1,n n,n+1 n+1,n+2 Two level system: Casperson, PRA 57, 609 (1998).

14. Hardening of softmode in SrTiO 3 thin film kBTkBT Katayama MN et al. CLEO/QELS 2010

15. THz pump-vis probe spectroscopy in ZnSe MQW system Hirori, MN, Tanaka, PRB 81, 081305(R) (2010). MQWs THz pump pulse probe optical pulse at 10 K n B =1 V r eh Exciton resonance disappears with blue shift E ex /ea B = 70 kV/cm

16. THz motions of WATER Fukasawa et al. PRL 95, 197802 (2005) Huge orientational relaxation mode, related to hydrogen bonding network, lies in THz frequency region. Raman tensor at low frequency is little, so it is difficult to drive water molecules via Raman induced Kerr effect. Dielectric tensor Raman tensor

17. Response of water in 100  m silica cell Single THz pulse responses of water MN and Tanaka CLEO/QELS 2010

18. Temporal evolution of dielectric constant of water (c) MN and Tanaka CLEO/QELS 2010

19. Even with sub-mW injection, temperature of orientational motion increase a few tens K. Rotational motion is driven without thermal relaxation (or before heating other modes) Yada, MN, Tanaka, CPL (2008). Driving orientational motion of water

20. Hydrogen bonding network controlled with THz pulse We can control water properties as SOLVENT in ps timescale, which influence chemical reactions of solute molecules. MN and Tanaka CLEO/QELS 2010

21. Summary We succeed intense THz pulse generation with >200 kV/cm field amplitude. We demonstrate THz nonlinearity of vibration modes in amino acide microcrystal and dielectric materials. Experimental results is interpreted with ladder climbing in anharmonic potential. We demonstrate huge spectrum modulation near the bandgap of semiconductors with intense THz pulse, which shows non- perturbed nonlinear regime. We observe water molecules driven by intense THz pulses. This motions is different from thermal effects. Results show the reorientational motion of water molecules with breaking hydrogen bonding in several picosecond timescale.