SMP@Lens


We are a group of researchers working at the European Lab. for Non-Linear Spectroscopy (LENS), University of Firenze in Italy. We are studying complex materials, mainly soft matter by laser spectroscopy. In this site you can find a very short summary of our present and past work. For information you can contact:

Renato Torre, PhD
European Lab. for Non-Linear Spectroscopy (LENS)
and Dpt. of Physics and Astronomy, Univ. of Firenze
Via Carrara 1, 50019 Sesto Fiorentino, Firenze, Italy
Tel: #39-055-4572495; skype: rena.torre
torre@lens.unifi.it; renato.torre@unifi.it; 


Our research interest is on the experimental investigation of "Soft Matter Physics", this focuses on the study of a variety of physical systems whose properties are intermediate between liquid and solid states. All these materials, despite their very different nature, share an important common physical feature: soft matter self-organizes into mesoscopic structures that are much larger than the microscopic scale and yet are much smaller than the macroscopic (overall) scale of the material. At LENS we study structure and dynamics of soft matter by means time-resolved laser spectroscopy, exciting the sample impulsively. It is thus possible to follow the sample response over a very wide time scale, from picosecond to millisecond, and investigate a variety of soft matter properties, including molecular vibrations, structural-rotational relaxation, elastic-acoustic propagation and thermal diffusion.

Our present researches are :

the ultrafast dynamics of the supercooled water by optical Kerr effect (OKE).

the properties of nano-confined liquids both by OKE and transient grating experiments (TG), measuring the acoustic propagation, the flow and thermal diffusion phenomena at the nanoscale.

the phononic properties of nano-structured surfaces by reflecting TG experiments. 

the development of THz laser sources and Time Domain Spectroscopy set-ups in this unexplored frequency range.



.... see also :
Torre, R. (2008). Time-Resolved Spectroscopy in Complex Liquids, An Experimental Perspective. Boston, MA: Springer US. doi:10.1007/978-0-387-25558-3



New Researches and Highlights


THz radiation and artwork investigations

THz pulse imaging and spectroscopy is an emerging non-invasive method for the char
acterization of cultural heritage artefacts that provides complementary information to tra
ditional analytical tools.
We explored artworks drawing materials with THz-Time Domain Spectro
scopy (THz-TDS) extending the investigation to thin layers of inks, that was never realized 
previously. We developed a new speci.c experimental method and data analysis to disen
tangle the multiple re
ection signals. Thanks to a high signal to noise ratio and the accurate 
analysis implemented, our measurements enable the calculation of the absolute absorption 
coeffi.cient and index of refraction of the materials, as well as the sample thickness down to 
tens of microns both in single layer and bilayer con.gurations.

Thin layered drawing media probed by THz time-domain spectroscopy
J. TassevaA. TaschinP. BartoliniJ. StriovaR. FontanaR. Torre

Dynamics of Liquid Water: recent experimental investigations

We presented an overview of  time-resolved vibrational spectroscopic studies of liquid water from ambient conditions to the supercooled state,The structure and dynamics of the complex hydrogen-bond network formed by water molecules are discussed, as well as the dissipation mechanism of vibrational energy throughout this network. A broad range of water investigations are addressed:infrared and Raman spectroscopy, femtosecond pump−probe, photon-echo, optical Kerr effect, sum-frequency generation, and two-dimensional infrared spectroscopic studies. By comparison of the complementary aspects probed by various linear and nonlinear spectroscopic techniques, a coherent picture of water dynamics and
energetics emerges. 


Perakis, F.; Marco, L.; Shalit, A.; Tang, F.; Kann, Z. R.; Kuhne, T. D.; Torre, R.; Bonn, M.; Nagata, Y.
Vibrational Spectroscopy and Dynamics of Water.



Local Structures of Liquid Water

The liquid and supercooled states of water show a series of anomalies whose nature is debated. A key role is attributed to the formation of structural aggregates induced by critical phenomena occurring deep in the supercooled region; the nature of the water anomalies and of the hidden critical processes remains elusive. Here we report a time-resolved optical Kerr effect investigation of the vibrational dynamics and relaxation processes in supercooled bulk water. The experiment measures the water intermolecular vibrations and the structural relaxation process in an extended temperature range, and with unprecedented data quality. A mode-coupling analysis of the experimental data enables to characterize the intermolecular vibrational modes and their interplay with the structural relaxation process. The results bring evidence of the coexistence of two local configurations, which are interpreted as high-density and low-density water forms, with an increasing weight of the latter at low temperatures.
The time-resolved optical Kerr effect spectroscopy (OKE) is a powerful experimental tool enabling accurate investigations of the dynamic phenomena in molecular liquids. We introduced innovative experimental and fitting procedures, that permit a safe deconvolution of sample response function from the instrumental function. This is a critical issue in order to measure the dynamics of sample presenting weak signal, e.g. liquid water. The unpreceded data quality makes possible a solid comparison with few theoretical models; the multi-mode Brownian oscillator model, the Kubo's discrete random jump model and the schematic mode-coupling model. All these models produce reasonable good fits of the OKE data of stable liquid water, i.e. over the freezing point. The features of water dynamics in the OKE data becomes unambiguous only at lower temperatures, i.e. for water in the metastable supercooled phase. Hence this data enable a valid comparison between the model fits. We found that the schematic mode-coupling model provides the more rigorous and complete model for water dynamics.

Optical Kerr Effect of Liquid and Supercooled Water: The Experimental and Data Analysis Perspective.
A. Taschin, P. Bartolini, R. Eramo, R. Righini, and R. Torre.
Journal of Chemical Physics, 141, 084507 (2014).

Evidence of two distinct local structures of water from ambient to supercooled conditions. 
Taschin, A., Bartolini, P., Eramo, R., Righini, R. & Torre, R. 
Nat. Commun. 4, 1–8 (2013),



Nanoconfined Water

We investigate the vibrational dynamics and the structural relaxation of water nanoconfined in Vycor porous silica samples (pore size 4 nm) at different levels of hydration and temperatures. At low level of hydration, corresponding to two complete superficial water layers, no freezing occurs and water remains mobile at all the investigated temperatures with dynamic features similar, but not equal, to the bulk water. The fully hydrated sample shows formation of ice at about 248 K, this processes does not involve all the contained water; a part of it remains in a supercooled phase.
The spectra are obtained as the Fourier transforms of time-resolved heterodyne detected optical Kerr effect (HD-OKE) measurements. The comparison of these spectra with that of bulk water enables us to separately extract and analyze the spectral contributions of the first and second hydration layers, as well as that of bulk-like inner water. We conclude that the extra water entering the pores above ≈ 10 % water/silica weight ratio behaves very similarly to bulk water. At lower levels of hydration, corresponding to two complete superficial water layers or less, the H-bond bending and stretching bands, characteristic of the tetrahedral coordination of water in the bulk phase, progressively disappear: clearly in these conditions the H-bond connectivity is very different from that of liquid water.

A comparative study on bulk and nanoconfined water by time-resolved optical Kerr effect spectroscopy
Taschin, Andrea, Bartolini, P., Marcelli, A., Righini, R., & Torre, R. 2013.

Supercooling and Freezing Processes in Nanoconfined Water by Time-Resolved Optical Kerr Effect Spectroscopy
Taschin, A., P. Bartolini, A. Marcelli, R. Righini, and R. Torre. 2014.

Confinement, entropic effects and hydrogen bond network fluctuations of water in Nafion membrane
Plazanet, M.,  Torre, R.,  Sacchetti, F. 


THz Dynamics of Nanoconfined Water by Ultrafast Optical Spectroscopy,
Taschin A.,  Bartolini P. and Torre R.Measurement Science and Technology (2016), in press
arXiv:1604.08746


High-Precision Terahertz Spectroscopy

Trace-gas sensing with high sensitivity and precision in the terahertz regime can be important in environmental monitoring, security, and astrophysics, as well as in tests of fundamental physics. Now, as reported in Physical Review X, a research team has performed the first terahertz spectroscopic measurements using a so-called frequency comb—a technique that allows frequency measurements with extremely high accuracy. As a proof-of-principle, the team measured a rotational transition in a gas molecule (methanol) to a precision of 4 parts in one billion, 10 times better than the previous record. The result is also twice as precise as the theoretically predicted frequency, suggesting the technique could help refine theoretical models.



Frequency-Comb-Assisted Terahertz Quantum Cascade Laser Spectroscopy
S. Bartalini, L. Consolino, P. Cancio, P. De Natale, P. Bartolini, A. Taschin, M. De Pas, H. Beere, D. Ritchie, M. S. Vitiello, and R. Torre
Phys. Rev. X 4, 021006 (2014)