[show abstract][hide abstract] ABSTRACT: We report on the laser action in a microcavity where both the dielectric mirrors and the active material have a macromolecular nature, resulting in a full plastic laser device. Distributed Bragg reflectors (DBRs) are prepared by spin-coating of polyvinylcarbazole and cellulose acetate orthogonal solutions and the active layer consists of a highly fluorescent conjugated polymer poly(9,9-dioctylfluorenyl-2,7-diyl-co-1,4-benzo-(2,1'-3)-thiadiazole) (F8BT) spun film. A quality factor in the range 80–180 is achieved and the cavity mode is carefully tuned on the peak of the F8BT amplified spontaneous emission spectrum. Under pulsed optical pumping, laser emission is obtained with a surprisingly low lasing threshold (<20 μJ cm−2) for a full plastic DBR optical cavity. This result opens a simple and cheap way to obtain a new class of polymer lasers.
[show abstract][hide abstract] ABSTRACT: We study the generation of high order harmonics produced by the
interaction of three intense and ultrafast noncollinear laser pulses.
Harmonic radiation, not overlapped to the direction of the incident
pulses, is observed.
[show abstract][hide abstract] ABSTRACT: Optical Projection Tomography (OPT) is a three dimensional imaging
technique that is particularly suitable for studying millimeter sized
biological samples and organisms. Similarly to x-ray computed
tomography, OPT is based on the acquisition of a sequence of images
taken through the sample at many angles (projections). Assuming the
linearity of the optical absorption process, the projections are
combined to reconstruct the 3-D volume of the sample, typically using a
filtered back-projection algorithm. OPT has been applied to in-vivo
imaging of zebrafish (Danio rerio). The instrument and the protocol for
in vivo imaging of zebrafish embryos and juvenile specimens are
described. Light scattering remains a challenge for in vivo OPT,
especially when samples at the upper size limit, like zebrafish at the
adult stage, are under study. We describe Time-Gated Optical Projection
Tomography (TGOPT), a technique able to reconstruct adult zebrafish
internal structures by counteracting the scattering effects through a
fast time-gate. The time gating mechanism is based on non-linear optical
upconversion of an infrared ultrashort laser pulse and allows the
detection of quasi-ballistic photons within a 100 fs temporal gate. This
results in a strong improvement in contrast and resolution with respect
to conventional OPT. Artifacts in the reconstructed images are reduced
as well. We show that TGOPT is suited for imaging the skeletal system
and nervous structures of adult zebrafish.
[show abstract][hide abstract] ABSTRACT: In this work we present a procedure for the reconstruction of the
Highest Occupied Molecular Orbital in carbon dioxide by exploiting the
generation of high order harmonics in a sample of impulsively aligned
molecules. The procedure allows to extract the single molecule
contribution to the harmonic spectrum in both amplitude and phase as a
function of angular orientation and photon energy and to exploit this
information in the reconstruction of the orbital. The role of
multielectron contributions and of the Coulomb field of the ion on the
reconstruction are discussed.
[show abstract][hide abstract] ABSTRACT: High-order harmonic generation is as a powerful tool for the study of
molecular properties. Up to now this investigation tool has been
confined to simple molecules, with a relatively high ionization
potential, since ionization saturation hindered its exploitation to
fragile molecules. In this work we show that such limitation can be
overcome by using mid-IR ultrashort driving pulses; as prototypical
molecules we considered hydrocarbons. Clear signatures of the highest
occupied molecular orbital were found in the harmonic spectra generated
in unsaturated aligned hydrocarbons like acetylene, ethylene, allene and
1,3-butadiene. Our findings demonstrate that high-order harmonic
generation spectroscopy can be extended to complex molecular species.
Multiphoton Processes and Attosecond Physics (ICOMP12). 01/2012;
[show abstract][hide abstract] 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.
PLoS ONE 01/2012; 7(11):e50744. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The production of isolated attosecond pulses is nowadays based on the generation of
high harmonics driven by ultrafast and intense laser sources in gases. The generation of such pulses
requires the confinement of the harmonic emission within a single event, thus obtaining a continuous
XUV spectrum. Here we report on the generation of continuous XUV spectra produced by an ultrabroadband
optical parametric amplifier operating in the mid-IR and generating multi-cycle pulses,
thus avoiding the use of few-cycle Ti:sapphire lasers and, thanks to the favorable cutoff scaling law
for mid-IR drivers, paving the way to the production of isolated attosecond pulses well above the
100-eV photon energy.
[show abstract][hide abstract] ABSTRACT: High-order harmonic generation is nowadays a topic of crucial interest
since it allows the production of isolated attosecond pulses. Several
efforts have been made so far for extending the generation of attosecond
bursts beyond the 100 eV spectral region, in order to access to deeper
electronic states in atoms and molecules. Recently, mid-infrared laser
sources have demonstrated to be ideal candidates for pushing the high
harmonic emission up to the soft X-rays. Here we show that it is
possible to obtain continuous harmonic spectra, that are the signature
of single attosecond pulse generation, by properly mixing two laser
pulses, coming from optical parametric amplifiers, with wavelengths of
1.35 and 1.75 μm respectively, with either parallel or perpendicular
polarizations. Our results demonstrate the generation of isolated
attosecond burst driven by mid-infrared laser pulses of a duration
larger than 30 fs.
Multiphoton Processes and Attosecond Physics (ICOMP12). 01/2012;
[show abstract][hide abstract] ABSTRACT: High-order harmonics of ultrashort laser pulses appear in the time domain as a sequence of attosecond bursts of coherent extreme ultraviolet radiation separated by half the optical cycle of the laser field. In order to confine this emission to an isolated attosecond pulse, suitable gating techniques have been proposed and investigated. In this work, we review a few gating techniques used in our laboratories, along with the basic tools for the generation and application of attosecond pulses.
Journal of Physics B Atomic Molecular and Optical Physics 01/2012; 45(7). · 2.03 Impact Factor
[show abstract][hide abstract] ABSTRACT: Imaging of the outermost molecular orbital by high-order harmonic
generation has been limited so far to very simple molecules like
nitrogen, since several difficulties had to be overcome in order to
extend it to more complex species. In this work we show that molecular
imaging can be applied to a triatomic molecule like carbon dioxide,
hence paving the way to the exploitation of such technique to the
imaging of polyatomic species.
Multiphoton Processes and Attosecond Physics (ICOMP12). 01/2012;
[show abstract][hide abstract] ABSTRACT: A two-color (1350+1750 nm) parametric source with passive stabilization of the carrier-envelope phase was exploited for the generation in noble gases of coherent continuous XUV spectra extending beyond 100 eV.
[show abstract][hide abstract] ABSTRACT: Ultrafast birefringence induced by filamentation-based rotational excitation in Nitrogen is exploited to modulate the polarization state of a probe pulse. This modulation is effectively employed for controlling high-order harmonic generation in Argon.
[show abstract][hide abstract] ABSTRACT: High resolution x-ray spectra of plasmas produced by the interaction of Ti:Sa laser pulses (duration from 60 fs to 1 ps, and energy from 15 to 128 mJ) with a solid iron target are investigated. Interestingly, both L-shell and K-shell Fe spectra were simultaneously measured using a focusing spectrometer with spatial resolution. In particular, the L-shell Fe radiation from F-, Ne-, and Na-like ions between ~14-16.3 Å were observed from the first-order reflection with a mica crystal. Simultaneously measured alongside the L-shell radiation was the Fe cold Kalpha lines (~1.94 Å), from eighth-order reflection. Two non-LTE Fe kinetic models have been developed to account for the L-shell radiation from the Fe ions and for the K-shell radiation from low ionization stages emitting the Fe cold Kalpha lines. Preliminary analysis of the simultaneously measured Fe L- and K-shell radiations from changing the time-duration, laser contrast, and focus of the experiments shows varying relative line intensities from different ionization stages. Resulting plasma parameters and their dependence on changing the time-duration, laser contrast, and laser focus will be discussed.
Journal of Physics B Atomic Molecular and Optical Physics 01/2011; 44(6). · 2.03 Impact Factor
[show abstract][hide abstract] ABSTRACT: The emission of coherent XUV radiation from atomic or molecular gases exposed to intense infrared laser pulses, known as high harmonic generation, is of paramount interest in atomic and molecular physics as well as in attosecond science. The emitted radiation contains a wealth of information about the structure of its generating medium, which inspired vigorous efforts to tomographically image the valence orbital of atoms and molecules. The orbital retrieval is nevertheless seriously hindered by the complexity of the harmonic emission process, as recently demonstrated by several theoretical and experimental works. Here we present a novel approach for molecular orbital tomography that contributes to overcome those difficulties, opening intriguing perspectives on coherent XUV imaging of complex species by high-order harmonic generation.
[show abstract][hide abstract] ABSTRACT: We experimentally demonstrate a new technique for
the temporal gating of high-order harmonic generation, based
on the mixing of two mid-infrared laser pulses coming from optical
parametric amplifiers, at wavelengths of 1.35 and 1.75 μm,
respectively. Both parallel and perpendicular configurations of
the polarization directions were investigated. Results obtained
in xenon and argon show continuous spectra with a significant
cutoff extension, up to 160 eV. These outcomes demonstrate
the possibility of extending the two-color gating technique for
the generation of isolated attosecond bursts to a mid-infrared
laser source and are, to our knowledge, the first experimental
demonstration of the gating on a single half-cycle of high-order
harmonics driven by laser pulses longer than 30 fs.
[show abstract][hide abstract] ABSTRACT: Based on the Magneto-Optical Kerr Effect (MOKE), we have developed an experimental set-up that allows us to fully characterize the magnetization dynamics in thin magnetic films by measuring all three real space components of the magnetization vector M. By means of the pump-probe technique it is possible to extract the time dependence of each individual projection with sub-picosecond resolution. This method has been exploited to investigate the temporal evolution of the magnetization (modulus and orientation) induced by an ultrashort laser pulse in thin epitaxial iron films.According to our results, we deduced that the initial, sub-picosecond demagnetization is established at the electronic level through electron-magnon excitations. The subsequent dynamics is characterized by a precessional motion on the 100 ps time scale, around an effective, time-dependent magnetic field. Following the full dynamics of M, the temporal evolution of the magneto-crystalline anisotropy constant can be unambiguously determined, providing the experimental evidence that the precession is triggered by the rapid, optically-induced misalignment between the magnetization vector and the effective magnetic field.These results suggest a possible pathway toward the ultrarapid switching of the magnetization.
[show abstract][hide abstract] ABSTRACT: We have demonstrated the ability of few-cycle midinfrared intense laser pulses to produce extended harmonic spectra ( ≥ 45 eV) suitable for high harmonic spectroscopy in aligned hydrocarbons with ionization potentials in the range 9.07–11.52 eV. Modulations in the spectra measured with different alignment angles show signatures of the molecular structure. These results pave the way for the extension of high harmonic spectroscopy to complex biomolecules.
[show abstract][hide abstract] ABSTRACT: We report on the generation of ultra-broadband laser pulses in the near and mid-infrared by Optical Parametric Amplifiers (OPAs). The wide tunability is obtained by using three different OPA configurations with pulse durations down to two optical cycles.
Optical Communication (ECOC), 2010 36th European Conference and Exhibition on; 10/2010
[show abstract][hide abstract] ABSTRACT: We have quantitatively characterized the real-space components of the magnetization vector M in thin epitaxial Fe(001)/MgO(001) films through an experimental set-up based on the magneto-optical Kerr effect. The capabilities of the method permit to investigate the magnetization reversal under the effect of an applied field directly on the real-space trajectories of M , providing a straightforward interpretation of the magnetization switching mechanisms in terms of magnetic anisotropies and domains formation. Using the pump-probe technique we also studied the three-dimensional precession dynamics of the magnetization vector triggered by a femtosecond laser pulse, revealing how the anisotropy fields (magnetocrystalline and shape) affect the observed features of the precessional dynamics, i.e., the frequency and the amplitude of motion. Our quantitative approach permits a deeper understanding of the basic mechanisms underlying spin dynamics and it can be successfully applied to a large class of magnetic thin layers.
Journal of Applied Physics 10/2010; · 2.21 Impact Factor
[show abstract][hide abstract] ABSTRACT: High resolution X-ray spectra of plasmas produced by the interaction of Ti:Sa laser pulses (duration from 60 fs to 1 ps, and energy from 15 mJ to 128 mJ) with a solid Fe target are investigated experimentally and theoretically. Interestingly, both L-shell and K-shell Fe spectra were simultaneously measured while changing the time-duration of the laser experiments. In particular, the L-shell Fe radiation from F-, Ne-, and Na-like ions between ~14–16.3 Å were observed from the first order reflection with a mica crystal. Simultaneously measured alongside the L-shell radiation was the Fe cold Kα lines (~1.94 Å), from 8th order reflection. Two non-LTE Fe kinetic models have been developed to account for the L-shell radiation from the Fe ions and for the K-shell radiation from the low ionization stages emitting the Fe cold Kα lines. Preliminary analysis of the simultaneously measured Fe L- and K-shell radiations from changing the time-duration of the experiments shows varying relative line intensities from different ionization stages. Resulting plasma parameters as well as the opacity of the strongest resonance line, 3C, and their dependence on changing the time-duration will be discussed.
Journal of Physics Conference Series 09/2010; 244(4):042004.