research experience

I have a wide experimental experience, since 1990, with laser sources of different types and application of these sources to perform complex optical spectroscopic investigations. In particular, I have a very good knowledge of pulsed laser systems of different nature and their utilization to realize time-resolved non-linear spectroscopic investigations. I started with the dye lasers producing tunable pico-second pulses. During the pioneering years, 1990-1995, of pulsed tunable laser I realized the laser cavity and the amplification stage and utilized this laser systems to measure the Time-Resolved Coherent Antistokes Raman Spectroscopy (CARS) of the molecular vibrations of benzene studying both the experimental determination of the non-linear response and the molecular dynamic problem. In the following, during my research period at the Stanford University in collaboration with prof. M.D.Fayer, I realized a laser system producing femto-second laser pulses at high repetition rate. This innovative laser systems enable to study the relaxation phenomena in liquid crystals approaching the isotropic-nematic phase transition. I studied also the Second Harmonic Generation from metal surfaces characterizing the propagation and scattering of “plasmons”. Detecting the electronic resonance of a beta-carotene we measured the rotational dynamics in the time-domain. As well, using the fluorescence spectroscopy time-resolved with single photon counting detection, I measured the energy transfer processes and single molecule dynamics.

With the realization of reliable commercial femto-second laser sources, based on Kerr-lens mode-locking phenomena, the time-resolved non-linear spectroscopy move from a pioneering tools to a mature investigation technique. I built and utilized several femto-second laser systems with Ti:Sapphire as active medium, both producing pulses of low-energy/high rep. rate and high-energy/low rep. rate. Using these laser sources I measured the non-linear response of several material giving a new insight of the matter proprieties.

Since 1992, I have been interested in the study of the dynamics of complex liquids. In particular in the aggregation and correlation processes taking place in the vicinity of a phase transition that transform a simple liquid into a structured liquid or into a meso-phase. These particular liquid states are interesting because acquire some universal features that are independent by their molecular nature. A lot of my work has been focused on the glass transition and supercooled liquids. We published a pioneering work on the measure by optical Kerr effect of the structural relaxation of a glass-former and its interpretation by mode-coupling theory [Torre, R., Bartolini, P. & Pick, R. Time-resolved optical Kerr effect in a fragile glass-forming liquid, salol. Phys. Rev. E 57, 1912–1920 (1998)].

Later I performed many different experimental studies measuring the structural relaxation and the viscoelastic proprieties of many glass-formers, evidencing the recurrent and universal dynamic laws that define the particular states of matter.

Between the glass-former liquid WATER likely the most important. I performed a measurement of the fast structural relaxation of water by time-resolved, showing for the first time its non-exponential decay and the critical slowing down of the relaxation times in the supercooled phase [Torre, R., Bartolini, P. & Righini, R. Structural relaxation in supercooled water by time-resolved spectroscopy. Nature 428, 296–299 (2004)]. This paper gives new insight into the nature of water physics and its glassy states. We are pursuing the study of metastable phases of water by experimental investigation of acoustic features and vibrational features. We measured the modification on water proprieties induced by nano-confinement into hydrophilic channels or polymeric membrane. Also the aqueous ionic solutions can give very valuable information on the water non-equilibrium properties. Recently we pursuit the OKE investigation on supercooled water measuring the vibrational dynamics [Taschin, A., Bartolini, P., Eramo, R., Righini, R. & Torre, R. Evidence of two distinct local structures of water from ambient to supercooled conditions. Nat. Commun. 4, 2401 (2013)].

Moreover, I began to investigated innovative spectroscopic techniques based THz radiation [Consolino, L. et al. Phase-locking to a free-space terahertz comb for metrological-grade terahertz lasers. Nat. Commun. 3, 1040 (2012)]. Using a non-linear crystal response it is possible to convert the optical femto-second laser pulse into THz pulse radiation with the a time duration of about one picosecond. These new pulsed radiation open the possibility to investigate a very interesting and almost unknown spectrum of the matter response. Covering the 0.1-10 GHz spectrum of frequency this radiation enable the investigation of collective roto-vibrational mode in no transparent materials, including all the biological systems. Moreover, I am realizing an improvement of the time-resolved non-linear spectroscopic techniques towards a spatial sub-micron spatial resolution that will enable innovative real-time microscopic imaging of the material dynamics.

I am working at LENS that represents a very international and interdisciplinary platform to develop any new spectroscopic tools. The synergy of these spectroscopic skills with the bio-medical group needs will open new points of view that will turn into breakthrough knowledge and technology.