172 research outputs found
Self-reconstructing all-optical poling in polymer fibers
Self-sustained all-optical poling second-harmonic generation (SHG) experiments are conducted in single-core and multicore dye-doped poly(methyl methacrylate) optical fibers. By tuning the polarization of the fundamental beam, the SHG signal is degraded and is reconstructed spontaneously up to its initial level. We found a new situation in which the photo-induced self-organization of azo polymers creates a well-ordered periodic structure
Nonlinear effetcts in dye-doped polymer optical fibres for optical communication
We review experimental studies of nonlinear optics in large-core dye doped plastic optical fibres. In particular second-order nonlinearity in all-optical poled optical fiber is promising for application to electro-optic switching, second-harmonic generation, and frequency conversion
Stable frequency doubling by all-optical poling in dye-doped polymer optical fibers
We present experimental studies of all-optical poling (AOP) in large-core dye-doped poly(methyl methacrylate) plastic optical fibers. We show that the confinement of light within the fiber core permits us to reach the upper limit of second harmonic generation achievable by AOP using repeated trans-cis isomerization. Quantification of the output power indicates self-seeding that can counteract relaxation of the orientation during readout of the induced nonlinearity
Multiphoton absorption in amyloid protein fibres
Fibrillization of peptides leads to the formation of amyloid fibres, which, when in large aggregates, are responsible for diseases such as Alzheimer's and Parkinson's. Here, we show that amyloids have strong nonlinear optical absorption, which is not present in native non-fibrillized protein. Z-scan and pump-probe experiments indicate that insulin and lysozyme β-amyloids, as well as α-synuclein fibres, exhibit either two-photon, three-photon or higher multiphoton absorption processes, depending on the wavelength of light. We propose that the enhanced multiphoton absorption is due to a cooperative mechanism involving through-space dipolar coupling between excited states of aromatic amino acids densely packed in the fibrous structures. This finding will provide the opportunity to develop nonlinear optical techniques to detect and study amyloid structures and also suggests that new protein-based materials with sizable multiphoton absorption could be designed for specific applications in nanotechnology, photonics and optoelectronics
Gallium transformation under femtosecond laser excitation: Phase coexistence and incomplete melting
The reversible phase transition induced by femtosecond laser excitation of
Gallium has been studied by measuring the dielectric function at 775 nm with ~
200 fs temporal resolution. The real and imaginary parts of the transient
dielectric function were calculated from absolute reflectivity of Gallium layer
measured at two different angles of incidence, using Fresnel formulas. The
time-dependent electron-phonon effective collision frequency, the heat
conduction coefficient and the volume fraction of a new phase were restored
directly from the experimental data, and the time and space dependent electron
and lattice temperatures in the layer undergoing phase transition were
reconstructed without ad hoc assumptions. We converted the temporal dependence
of the electron-phonon collision rate into the temperature dependence, and
demonstrated, for the first time, that the electron-phonon collision rate has a
non-linear character. This temperature dependence converges into the known
equilibrium function during the cooling stage. The maximum fraction of a new
phase in the laser-excited Gallium layer reached only 60% even when the
deposited energy was two times the equilibrium enthalpy of melting. We have
also demonstrated that the phase transition pace and a fraction of the
transformed material depended strongly on the thickness of the laser-excited
Gallium layer, which was of the order of several tens of nanometers for the
whole range of the pump laser fluencies up to the damage threshold. The
kinetics of the phase transformation after the laser excitation can be
understood on the basis of the classical theory of the first-order phase
transition while the duration of non-thermal stage appears to be comparable to
the sub-picosecond pulse length.Comment: 28 pages, including 9 figs. Submitted to Phys. Rev. B 14 March 200
Nonlinear absorption and nonlinear refraction: Maximizing the merit factors
Both nonlinear absorption and nonlinear refraction are effects that are potentially useful for a plethora of applications in photonics, nanophotonics and biophotonics. Despite substantial attention given to these phenomena by researchers studying the merits of disparate systems such as organic materials, hybrid materials, metal-containing molecules and nanostructures, it is virtually impossible to compare the results obtained on different materials when varying parameters of the light beams and different techniques are employed. We have attempted to address the problem by studying the properties of various systems in a systematic way, within a wide range of wavelengths, and including the regions of onephoton, two-photon and three-photon absorption. The objects of our studies have been typical nonlinear chromophores, such as π-conjugated molecules, oligomers and polymers, organometallics and coordination complexes containing transition metals, organometallic dendrimers, small metal-containing clusters, and nanoparticles of various kinds, including semiconductor quantum dots, plasmonic particles and rare-earth doped nanocrystals. We discuss herein procedures to quantify the nonlinear response of all of these systems, by defining and comparing the merit factors relevant for various applications
Exceptionally large two- and three-photon absorption cross-sections by OPV organometalation
Oligo(p-phenylenevinylene)s (OPVs) containing up to 8 PV units and end-functionalized by ruthenium alkynyl groups have been prepared and their nonlinear absorption properties assessed using the Z-scan technique and employing low repetition rate femtosecond pulses. Exceptionally large two-photon absorption (ca. 12 500 GM at 725 nm) and three-photon absorption cross sections (ca. 1.6 × 10⁻⁷⁶ cm⁶s² at 1100 nm) are found for the 8PV-containing example, highlighting the potential of an “organometalation” approach to NLO-efficient organic materialsWe thank the Australian Research Council (ARC), the National
Natural Science Foundation of China (51432006), the Chinese
Government Ministry of Education, the Chinese Government State
Administration of Foreign Experts Affairs (111 Project: B13025), and
the National Science Centre of Poland (grant 2013/10/A/ST4/00114)
for financial support. M. P. C. thanks the ARC for an Australian
Research Fellowship and C. Q. thanks CONICYT (Chile) for a Chile
PhD Scholarship Abroad
Low-loss waveguides in ultrafast laser-deposited As(2)S(3) chalcogenide films
This paper was published in Journal of the Optical Society of America B and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/abstract.cfm?URI=josab-20-9-1844. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.A. Zakery, Y. Ruan, A. V. Rode, M. Samoc, and B. Luther-Davie
Evolution of Linear Absorption and Nonlinear Optical Properties in V-Shaped Ruthenium(II)-Based Chromophores
In this article, we describe a series of complexes with electron-rich cis-{Ru^(II)(NH_3)_4}^(2+) centers coordinated to two pyridyl ligands bearing N-methyl/arylpyridinium electron-acceptor groups. These V-shaped dipolar species are new, extended members of a class of chromophores first reported by us (Coe, B. J. et al. J. Am. Chem. Soc. 2005, 127, 4845−4859). They have been isolated as their PF_6− salts and characterized by using various techniques including ^1H NMR and electronic absorption spectroscopies and cyclic voltammetry. Reversible Ru^(III/II) waves show that the new complexes are potentially redox-switchable chromophores. Single crystal X-ray structures have been obtained for four complex salts; three of these crystallize noncentrosymmetrically, but with the individual molecular dipoles aligned largely antiparallel. Very large molecular first hyperpolarizabilities β have been determined by using hyper-Rayleigh scattering (HRS) with an 800 nm laser and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d → π^* metal-to-ligand charge-transfer (MLCT) and π → π^* intraligand charge-transfer (ILCT) bands. The latter measurements afford total nonresonant β_0 responses as high as ca. 600 × 10^(−30) esu. These pseudo-C_(2v) chromophores show two substantial components of the β tensor, β_(zzz) and β_(zyy), although the relative significance of these varies with the physical method applied. According to HRS, β_(zzz) dominates in all cases, whereas the Stark analyses indicate that β_(zyy) is dominant in the shorter chromophores, but β_(zzz) and β_(zyy) are similar for the extended species. In contrast, finite field calculations predict that β_(zyy) is always the major component. Time-dependent density functional theory calculations predict increasing ILCT character for the nominally MLCT transitions and accompanying blue-shifts of the visible absorptions, as the ligand π-systems are extended. Such unusual behavior has also been observed with related 1D complexes (Coe, B. J. et al. J. Am. Chem. Soc. 2004, 126, 3880−3891)
Fingerprints of Through-Bond and Through-Space Exciton and Charge π-Electron Delocalization in Linearly Extended [2.2]Paracyclophanes
New stilbenoid and
thiophenic compounds terminally functionalized
with donor–donor, acceptor–acceptor, or donor–acceptor
moieties and possessing a central [2.2]paracyclophane unit have been
prepared, and their properties interpreted in terms of through-bond
and through space π-electron delocalization (i.e., π-conjugations).
Based on photophysical data, their excited-state properties have been
described with a focus on the participation of the central [2.2]paracyclophane
in competition with through-bond conjugation in the side arms. To
this end, two-photon and one-photon absorption and emission spectroscopy,
as a function of temperature, solvent polarity, and pressure in the
solid state have been recorded. Furthermore, charge delocalization
through the [2.2]paracyclophane in the neutral state and in the oxidized
species (radical cations, dications and radical trications) has been
investigated, allowing the elucidation of the vibrational Raman fingerprint
of through-space charge delocalization. Thus, a complementary approach
to both “intermolecular” excitation and charge delocalizations
in [2.2]paracyclophane molecules is shown which can serve as models
of charge and exciton migration in organic semiconductors
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