Abstract-Energy transfer within the hydrogen bonding network of water following resonant terahertz excitation

1. Hossam Elgabarty, 
2. Tobias Kampfrath, 
3. Douwe Jan Bonthuis, 
4. Vasileios Balos, 
5. Naveen Kumar Kaliannan, 
6. Philip Loche, 
7. Roland R. Netz, 
8. Martin Wolf, 
9. Thomas D. Kühne,  
10. Mohsen Sajad

https://advances.sciencemag.org/content/6/17/eaay7074.full

Energy dissipation in water is very fast and more efficient than in many other liquids. This behavior is commonly attributed to the intermolecular interactions associated with hydrogen bonding. Here, we investigate the dynamic energy flow in the hydrogen bond network of liquid water by a pump-probe experiment. We resonantly excite intermolecular degrees of freedom with ultrashort single-cycle terahertz pulses and monitor its Raman response. By using ultrathin sample cell windows, a background-free bipolar signal whose tail relaxes monoexponentially is obtained. The relaxation is attributed to the molecular translational motions, using complementary experiments, force field, and ab initio molecular dynamics simulations. They reveal an initial coupling of the terahertz electric field to the molecular rotational degrees of freedom whose energy is rapidly transferred, within the excitation pulse duration, to the restricted translational motion of neighboring molecules. This rapid energy transfer may be rationalized by the strong anharmonicity of the intermolecular interactions.

Abstract-Coherent phonon spectroscopy of non-fully symmetric modes using resonant terahertz excitation

T. Huber^1,a), M. Ranke², A. Ferrer^1,3, L. Huber¹ and S. L. Johnson¹
http://scitation.aip.org/content/aip/journal/apl/107/9/10.1063/1.4930021
1 Institute for Quantum Electronics, Physics Department, ETH Zurich, CH-8093 Zurich, Switzerland
2 The Hamburg Centre for Ultrafast Imaging, Luruper Chaussee 149, D-22761 Hamburg, Germany
3 Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
a) Electronic mail: tihuber@phys.ethz.ch
Appl. Phys. Lett. 107, 091107 (2015); http://dx.doi.org/10.1063/1.4930021

We use intense terahertz (THz) frequency electromagnetic pulses generated via optical rectification in an organic crystal to drive vibrational lattice modes in single crystal Tellurium. The coherent modes are detected by measuring the polarization changes of femtosecond laser pulses reflecting from the sample surface, resulting in a phase-resolved detection of the coherent lattice motion. We compare the data to a model of Lorentz oscillators driven by the near-single-cycle broadband THz pulse. The demonstrated technique of optically probed coherent phonon spectroscopy with THz frequency excitation could prove to be a viable alternative to other time-resolved spectroscopic methods like standard THz time domainspectroscopy.