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Search Results: 1 - 10 of 1143 matches for " Giulio Cerullo "
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Micromanufacturing in Fused Silica via Femtosecond Laser Irradiation Followed by Gas-Phase Chemical Etching
Francesco Venturini,Maurizio Sansotera,Rebeca Martinez Vazquez,Roberto Osellame,Giulio Cerullo,Walter Navarrini
Micromachines , 2012, DOI: 10.3390/mi3040604
Abstract: Femtosecond laser irradiation followed by chemical etching (FLICE) with hydrogen fluoride (HF) is an emerging technique for the fabrication of directly buried, three-dimensional microfluidic channels in silica. The procedure, as described in literature, consists of irradiating a silica slab followed by chemical etching using hydrogen fluoride. With aqueous HF the etching process is diffusion-limited and is self-terminating, leading to maximum microchannel lengths of about 1.5 mm, while the use of low-pressure gaseous HF etchant can quickly produce 3 mm long channels with an aspect ratio (Length/Diameter) higher than 25. By utilizing this methodology the aspect ratio is not constant, but depends on the length of the channel. When the microchannel is short the aspect ratio increases quickly until it reaches a maximum length at around 1400 μm. Thereafter the aspect ratio starts to decrease slowly. In this paper we present a variation of the low-pressure gaseous HF etching method, which is based on the dynamic displacement of the etchant. This method results in a 13% increase in the aspect ratio (L/D = 29) at the expense of a low etching speed (4 μm/min).
Influence of the Chemical Design on the Coherent Photoisomerization of Biomimetic Molecular Switches
Léonard Jérémie,Polli Dario,Cerullo Giulio,Olivucci Massimo
EPJ Web of Conferences , 2013, DOI: 10.1051/epjconf/20134105006
Abstract: Ultrafast transient absorption spectroscopy reveals the effect of chemical substitutions on the photoreaction kinetics of biomimetic photoswitches displaying coherent dynamics. Ground state vibrational coherences are no longer observed when the excited state lifetime exceeds 300fs.
Non-equilibrium dynamics of photo-excited electrons in graphene: collinear scattering, Auger processes, and the impact of screening
Andrea Tomadin,Daniele Brida,Giulio Cerullo,Andrea C. Ferrari,Marco Polini
Physics , 2013, DOI: 10.1103/PhysRevB.88.035430
Abstract: We present a combined analytical and numerical study of the early stages (sub-100fs) of the non-equilibrium dynamics of photo-excited electrons in graphene. We employ the semiclassical Boltzmann equation with a collision integral that includes contributions from electron-electron (e-e) and electron-optical phonon interactions. Taking advantage of circular symmetry and employing the massless Dirac Fermion (MDF) Hamiltonian, we are able to perform an essentially analytical study of the e-e contribution to the collision integral. This allows us to take particular care of subtle collinear scattering processes - processes in which incoming and outgoing momenta of the scattering particles lie on the same line - including carrier multiplication (CM) and Auger recombination (AR). These processes have a vanishing phase space for two dimensional MDF bare bands. However, we argue that electron-lifetime effects, seen in experiments based on angle-resolved photoemission spectroscopy, provide a natural pathway to regularize this pathology, yielding a finite contribution due to CM and AR to the Coulomb collision integral. Finally, we discuss in detail the role of physics beyond the Fermi golden rule by including screening in the matrix element of the Coulomb interaction at the level of the Random Phase Approximation (RPA), focusing in particular on the consequences of various approximations including static RPA screening, which maximizes the impact of CM and AR processes, and dynamical RPA screening, which completely suppresses them.
High energetic excitons in carbon nanotubes directly probe charge-carriers
Giancarlo Soavi,Francesco Scotognella,Daniele Viola,Timo Hefner,Tobias Hertel,Giulio Cerullo,Guglielmo Lanzani
Physics , 2014, DOI: 10.1038/srep09681
Abstract: Theory predicts peculiar features for excited-state dynamics in one dimension (1D) that are difficult to be observed experimentally. Single-walled carbon nanotubes (SWNTs) are an excellent approximation to 1D quantum confinement, due to their very high aspect ratio and low density of defects. Here we use ultrafast optical spectroscopy to probe photogenerated charge-carriers in (6,5) semiconducting SWNTs. We identify the transient energy shift of the highly polarizable S33 transition as a sensitive fingerprint of charge-carriers in SWNTs. By measuring the coherent phonon amplitude profile we obtain a precise estimate of the Stark-shift and discuss the binding energy of the S33 excitonic transition. From this, we infer that charge-carriers are formed instantaneously with sizable quantum yield even upon pumping the first exciton, S11. The decay of the photogenerated charge-carrier population is well described by a model for geminate recombination in 1D, suggesting an initial charge carrier separation of the same order of the exciton correlation length.
Femtosecond Laser Microfabrication of an Integrated Device for Optical Release and Sensing of Bioactive Compounds
Diego Ghezzi,Rebeca Martinez Vazquez,Roberto Osellame,Flavia Valtorta,Alessandra Pedrocchi,Giuseppe Della Valle,Roberta Ramponi,Giancarlo Ferrigno,Giulio Cerullo
Sensors , 2008, DOI: 10.3390/s8106595
Abstract: Flash photolysis of caged compounds is one of the most powerful approaches to investigate the dynamic response of living cells. Monolithically integrated devices suitable for optical uncaging are in great demand since they greatly simplify the experiments and allow their automation. Here we demonstrate the fabrication of an integrated bio-photonic device for the optical release of caged compounds. Such a device is fabricated using femtosecond laser micromachining of a glass substrate. More in detail, femtosecond lasers are used both to cut the substrate in order to create a pit for cell growth and to inscribe optical waveguides for spatially selective uncaging of the compounds present in the culture medium. The operation of this monolithic bio-photonic device is tested using both free and caged fluorescent compounds to probe its capability of multipoint release and optical sensing. Application of this device to the study of neuronal network activity can be envisaged.
Carrier-envelope phase effects on the strong-field photoemission of electrons from metallic nanostructures
Bjoern Piglosiewicz,Slawa Schmidt,Doo Jae Park,Jan Vogelsang,Petra Gross,Cristian Manzoni,Giulio Cerullo,Christoph Lienau
Physics , 2013, DOI: 10.1038/nphoton.2013.288
Abstract: Sharp metallic nanotapers irradiated with few-cycle laser pulses are emerging as a source of highly confined coherent electron wavepackets with attosecond duration and strong directivity. The possibility to steer, control or switch such electron wavepackets by light is expected to pave the way towards direct visualization of nanoplasmonic field dynamics and real-time probing of electron motion in solid state nanostructures. Such pulses can be generated by strong-field induced tunneling and acceleration of electrons in the near-field of sharp gold tapers within one half-cycle of the driving laser field. Here, we show the effect of the carrier-envelope phase of the laser field on the generation and motion of strong-field emitted electrons from such tips. This is a step forward towards controlling the coherent electron motion in and around metallic nanostructures on ultrashort length and time scales.
Time-Gated Optical Projection Tomography Allows Visualization of Adult Zebrafish Internal Structures
Luca Fieramonti, Andrea Bassi, Efrem Alessandro Foglia, Anna Pistocchi, Cosimo D'Andrea, Gianluca Valentini, Rinaldo Cubeddu, Sandro De Silvestri, Giulio Cerullo, Franco Cotelli
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0050744
Abstract: Optical imaging through biological samples is compromised by tissue scattering and currently various approaches aim to overcome this limitation. In this paper we demonstrate that an all optical technique, based on non-linear upconversion of infrared ultrashort laser pulses and on multiple view acquisition, allows the reduction of scattering effects in tomographic imaging. This technique, namely Time-Gated Optical Projection Tomography (TGOPT), is used to reconstruct three dimensionally the internal structure of adult zebrafish without staining or clearing agents. This method extends the use of Optical Projection Tomography to optically diffusive samples yielding reconstructions with reduced artifacts, increased contrast and improved resolution with respect to those obtained with non-gated techniques. The paper shows that TGOPT is particularly suited for imaging the skeletal system and nervous structures of adult zebrafish.
Mode-matching in multiresonant plasmonic nanoantennas for enhanced second harmonic generation
Michele Celebrano,Xiaofei Wu,Milena Baselli,Swen Gro?mann,Paolo Biagioni,Andrea Locatelli,Costantino De Angelis,Giulio Cerullo,Roberto Osellame,Bert Hecht,Lamberto Duò,Franco Ciccacci,Marco Finazzi
Physics , 2014, DOI: 10.1038/nnano.2015.69
Abstract: Boosting nonlinear frequency conversion in extremely confined volumes remains a key challenge in nano-optics, nanomedicine, photocatalysis, and background-free biosensing. To this aim, field enhancements in plasmonic nanostructures are often exploited to effectively compensate for the lack of phase-matching at the nanoscale. Second harmonic generation (SHG) is, however, strongly quenched by the high degree of symmetry in plasmonic materials at the atomic scale and in nanoantenna designs. Here, we devise a plasmonic nanoantenna lacking axial symmetry, which exhibits spatial and frequency mode overlap at both the excitation and the SHG wavelengths. The effective combination of these features in a single device allows obtaining unprecedented SHG conversion efficiency. Our results shed new light on the optimization of SHG at the nanoscale, paving the way to new classes of nanoscale coherent light sources and molecular sensing devices based on nonlinear plasmonic platforms.
The coherent dynamics of photoexcited green fluorescent proteins
Riccardo A. G. Cinelli,Valentina Tozzini,Vittorio Pellegrini,Fabio Beltram,Giulio Cerullo,Margherita Zavelani-Rossi,Sandro De Silvestri,Mudit Tyagi,Mauro Giacca
Physics , 2001, DOI: 10.1103/PhysRevLett.86.3439
Abstract: The coherent dynamics of vibronic wave packets in the green fluorescent protein is reported. At room temperature the non-stationary dynamics following impulsive photoexcitation displays an oscillating optical transmissivity pattern with components at 67 fs (497 cm-1) and 59 fs (593 cm-1). Our results are complemented by ab initio calculations of the vibrational spectrum of the chromophore. This analysis shows the interplay between the dynamics of the aminoacidic structure and the electronic excitation in the primary optical events of green fluorescent proteins.
Light-control of the ultrafast demagnetization pathway in an antiferromagnetic insulator
Vera G. Sala,Stefano Dal Conte,Timothy A. Miller,Daniele Viola,Elenora Luppi,Valérie Véniard,Giulio Cerullo,Simon Wall
Physics , 2015,
Abstract: Ultrafast demagnetization is a complex process involving strong coupling between electronic, spin, and structural degrees of freedom which is dependent on the type of magnetic order and band structure. Controlling these interactions is key for developing magnetic devices that can fully exploit femto-magnetism. Here we show that energy and polarization tunable femtosecond light pulses can be used to control the demagnetization pathway in the antiferromagnetic insulator Cr2O3. We visualize how the demagnetization dynamics depends on the pump photon energy using transient second harmonic spectroscopy. This enables us to monitor changes to the magnetic and crystalline symmetry, revealing the key role played by phonons in the demagnetization process. The phonon symmetry can be selected through the colour and polarization of the pump pulse, providing control over the demagnetization process, which could lead to faster and more efficient control of magnetic order.
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