Ultrashort light pulse generation and application to the study of ultrafast phenomena in the matter
Research focus
The Peer review has evaluated this group as Excellent
The research activity has been pursued for more than twenty years and comprises the fields of ultrashort pulse generation and study of ultrafast phenomena. Hereafter the most recent research topics are reported: Coherent XUV radiation by high order harmonic generation High-order harmonic generation (HHG) is now a widely used technique for the production of coherent extreme-ultraviolet (XUV) and soft-X-ray radiation. The HHG process has recently opened the way to the generation of attosecond pulses and to molecular tomography. A particularly important parameter of the driving pulses, which significantly influences the generation process, is the carrier-envelope phase (CEP). We have investigated, both experimentally and theoretically, the role of the CEP of few- and multipleoptical- cycle driving pulses on harmonic generation process. In the context of molecular imaging using laser driven recollisions, the process of intramolecular quantum interference in high-order harmonic generation in impulsively aligned two-centers molecules has been experimentally investigated. Attosecond science Attosecond science is now a well-established research field, which promises to offer formidable tools for the investigation and control of fundamental atomic and subatomic electron processes. We have recently experimentally demonstrated that the use of the polarization gating method with few-cycle phase-stabilized driving pulses offers the possibility to generate broadband isolated attosecond pulses. We have generated and characterized isolated pulses with duration down to 130 as around 36-eV photon energy, which consist of less than 1.2 periods of the central frequency. Such XUV radiation source opens the way to a new regime in the applications of attosecond pulses, where a medium interacts with nearly single-cycle isolated attosecond pulses. Broad-band optical parametric amplifiers This research line focuses on the generation of few-optical-cycle light pulses broadly tunable from the ultraviolet to the near-infrared spectral region. Such 17 pulses are produced, starting from an amplified Ti:sapphire laser system, exploiting Optical Parametric Amplifiers (OPAs). Under suitable phasematching conditions, OPAs provide ultrabroad gain bandwidths and effective pulse shortening down to 5 fs. We have developed a unique system, based on two synchronized OPAs, with extreme temporal resolution and broad spectral coverage. This system is extensively used for pump-probe spectroscopy of organic molecules. Additionally, the OPAs are also used for the generation of passively CEP-stabilized pulses by difference-frequency generation. Device fabrication and materials Goals of this activity are: i) preparation of suitable samples for photophysical investigations; ii) realization of prototypes for application in opto-electronics and photonics. Conjugated molecules and polymers are deposited by spin coating, vacuum evaporation, drop-casting or dr. blading techniques on prepared substrates for producing thin films suitable for spectroscopy or active layers in devices. Metal contacts are deposited by high vacuum evaporation. OLED, photovoltaic cells, diode structures and photodiodes are prepared starting from clean, pre-patterned substrates, and characterized by standard electrical and optical measurements. Electro-absorption, chargeinduced absorption, photocurrent and cw-photoinduced absorption are carried out. Ultrafast spectroscopy and applications Early events of energy relaxation in photo-excited organic semiconductors and nanostructures are investigated by applying ultrafast non linear techniques, such as pump-probe, pump-push-probe, electric-field assisted pump-probe and cross-correlation photocurrent, in a broad spectral range and with time resolution from 200 fs to sub-10 fs. Main goal of the research activity is the discovery of phenomena which can be applied in optoelectronics or photonics. The activity also provides a background for understanding fundamental properties of materials with high technological impacts and general knowledge on the photophysics of p-electrons in nanostructures. Applications include polymer lasers (DFB or vertical cavities), all-optical switching, photovoltaic conversion and non-linear photo-diodes. Femtosecond nano-optics This novel research line combines the short pulsewidths of femtosecond lasers with the ultrahigh spatial resolution of the Scanning Near-field Optical Microscope (SNOM), to perform nonlinear optics at the nanoscale. We couple a femtosecond laser to an aperture SNOM, based on cantilevered hollow pyramids, and use it to image, with 100-nm spatial resolution, secondharmonic generation (SHG) and two-photon photoluminescence from metal nanostructures and organic films. We also propose a novel approach to scattering SNOM, in which femtosecond pulses are focused on a sharp metal tip. Field enhancement localizes SHG to its apex, obtaining an isolated nanosource of short light pulses.
Departments
Professors
Full Professors
De Silvestri Sandro
Svelto Orazio
Associate Professors
Cerullo Giulio
Lanzani Guglielmo
Nisoli Mauro
Stagira Salvatore
Assistant Professors
Polli Dario
Sansone Giuseppe
Zavelani-Rossi Margherita