Abstract-Nonlinear TeraHertz Transmission by Liquid Water at 1 THz

Fabio Novelli, Chun Yu Ma,Nidhi Adhlakha,Ellen M. Adams,Thorsten Ockelmann ,Debasish Das Mahanta,Paola Di Pietro, Andrea Perucchi, Martina Havenith

https://www.mdpi.com/2076-3417/10/15/5290

The solvation properties of liquid water originate from the transient network of hydrogen-bonded molecules. In order to probe the coupling between the different modes of this network, nonlinear terahertz (THz) spectroscopy techniques are required. Ideally, these techniques should use a minimal volume and capitalize on sensitive field-resolved detection. Here we performed open aperture z-scan transmission experiments on static liquid cells, and detect the THz fields with electro-optical techniques. We show that it is possible to quantify the nonlinear response of liquid water at ~1 THz even when large signals originate from the sample holder windows

Abstract-Molecular Alignment of Bulk Water: Observing a Giant THz Kerr Effect upon Librational Excitation

Fabio Novelli, Federico Sebastiani, Claudius Hoberg, Luis Ruiz Pestana, Kochise C. Bennett, Nikolas Stavrias, Lex A.F.G. Van Der Meer, Gerhard Schwaab, Teresa Head-Gordon, Martina Havenith

https://arxiv.org/abs/1809.04261

Induced orientation of a molecule in real space by static and intense laser fields has been successfully employed to control reactions in the gas phase. However, for bulk water an effective alignment was not realized, yet due to the fast energy dissipation into the water network. Here we report a nonlinear Terahertz (THz) experiment carried out at the free electron laser FELIX. At 11.7 THz we observe a giant, resonance enhanced Kerr parameter which exceeds previous values by 4 orders of magnitude. Using ab initio molecular dynamics calculations, the large THz Kerr effect can be rationalized in terms of a linear response of a driven resonance orientation upon excitation of single water rotations. Our results suggest that bulk water can be efficiently aligned by THz laser fields around 12 THz. 

Abstract-Terahertz thermometry of gold nanospheres in water

Fabio Novelli, James W. M. Chon, and Jeffrey A. Davis

The photo-thermal effects of plasmonic nanoparticles are promising for cancer therapies. These treatments would greatly benefit from real-time, multi-scale temperature mapping by non-invasive means. Here we show that intense terahertz time domain spectroscopy can be used as a non-contact and high-resolution thermometer of water solutions. Using this technique, we measure the temperature change, triggered by femtosecond amplified laser pulses, of a solution of gold nanospheres in water. Extensions of this ultra-fast and non-invasive technique could open the door to real-time micro-thermometry of single cells without fluorescent labels.

© 2016 Optical Society of America

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Abstract-Revealing hidden optical transitions with tuneable optical-pump THz-probe spectroscopy

Fabio Novelli, Jeffrey A Davis

(Submitted on 5 Aug 2016)

http://arxiv.org/abs/1608.01759

While a vast amount of theoretical and experimental approaches can be used to study the band structure of simple solids, the investigation of the electronic properties of high-temperature superconductors and other strongly correlated systems is far less simple. Limitations to both theory and experiments arise from e.g. the many-body nature of the mathematical problem and from the non-trivial surface reconstructions, respectively. Here we propose a novel approach able to reveal energy gaps between band extrema that cannot be identified from the equilibrium optical properties. By combining finely-tunable visible pump pulses with terahertz probe fields, we identify changes to the transient conductivity as the pump wavelength is changed and the density of carriers in different parts of the band structure varies. This approach is demonstrated on a typical semiconductor, undoped silicon, where we identify the band minimum at the L point of the conduction band, corresponding to the second lowest energy indirect gap. When carriers are photo-injected above this secondary energy gap the transmitted terahertz probe fields are dramatically affected. Our results open the possibility of novel, all optical experimental opportunities for the investigation of the ultra-fast electronic dynamics of correlated materials.