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Reports on the femtosecond time resolved photoinduced transmission studies on nanodrytalline dihexylsexithiophene films with long range structural order. Explanation on the lack of radiative recombination in the solid phase with the formation of two nonradiative excitations, dark excitons and charge transfer states; Experimental setup for pump-probe measurements.

Abstract: Ultrafast exciton dynamics is measured in films of functionalized single wall carbon nanotubes embedded in PMMA with time resolution down to sub-10-fs. Ultrafast bleaching decay and photoinduced absorption formation (depending on probe wavelength) are observed and assigned to decay of the second (or higher) exciton into the first exciton. The time constant of the relaxation process is ≈40fs. The origin of the phenomenon is discussed within the one-dimensional semiconductor picture. [Copyright &y& Elsevier]

We study the enhanced charge generation from higher excited states in a conjugated polymer via a modification of transient differential transmission spectroscopy. The first excited state S1 is reexcited via a second laser pulse towards a higher state Sn. The relaxation dynamics of Sn as well as the kinetics of the states created from Sn is revealed by a broad-band probe pulse.The push and probe durations below 20 fs allow the time-resolution of the Sn relaxation and enables us to identify the two main contributions to enhanced charge generation from Sn, energy migration and vibrational relaxation. [Copyright &y& Elsevier]

We probe the photoconductive response to optical re-excitation of photoexcitations in a four-member oligophenylenevinylene in a sandwich LED configuration. Re-excitation of the singlet exciton leads to an enhancement of photocurrent (PC). Only excitons in the vicinity of the aluminum electrode give rise to PCs. Also charged photoexcitations can be re-excited to form mobile charge carriers. We show that an increase of PC is only observed during the ultrashort period of geminate recombination, due to optically induced enhancement of the escape probability of the charged pairs. [Copyright &y& Elsevier]

Excited-state dynamics of four carotenoids with different chain length (neurosporene, lycopene, C44 and C50) in solution has been measured with sub-20 fs temporal resolution. After photoexcitation from the ground 11Ag− state (S0) to the optically allowed 11Bu+ state (S2), we observe ultrafast internal conversion to the lower-lying forbidden 21Ag− state (S1) taking place in a few hundred femtoseconds, followed by ground-state recovery within a few picoseconds. As the chain length (n) is increased from n=9 (neurosporene) to n=15 (C50), we observe an increase of both the S2→S1 and S1→S0 conversion rates, attributed to a decrease of the energy gap with conjugation length. [Copyright &y& Elsevier]

Here we report a detailed study of organic light-emitting diodes based on poly(9,9-dioctylfluorene) (PFO), to investigate polaron generation, due to field induced singlet dissociation, and their subsequent recombination. We find that initially free polarons coalesce into intermediate pairs of both singlets and triplets multiplicity which subsequently decay into the neutral state. There is indication that the efficiency of singlet formation (β=0.7) is much higher than expected from simple state degeneracy arguments (β=0.25). [Copyright &y& Elsevier]

We present the first direct evidence of the presence of an intermediate singlet excited state (S[subx]) mediating the internal conversion from S[sub2] to S[sub1] in carotenoids. The S[sub2] to S[subx] transition is extremely fast and is completed within approximately 50 femtoseconds. These results require a reassessment of the energy transfer pathways from carotenoids to chlorophylls in the primary step of photosynthesis. [ABSTRACT FROM AUTHOR]

Abstract. Many fundamental processes of radiation-matter interaction, which take place on the ultra-short time scale, can now be directly investigated by using few-optical-cycles light pulses with duration < 10 fs. We discuss two techniques for generating such pulses: broad-band parametric amplification, which allows the generation of pulses in the visible range suitable for spectroscopy, and compression of high-energy light pulses in a hollow fiber. As an example of application in time-resolved spectroscopy we report results of pump-probe experiments in a prototypical conjugated molecule, namely sexithiophene. The new laser sources, due to their characteristics of peak power and coherence, also allow the exploration of new fields of experimental physics, such as extreme nonlinear optics. We focus on high-order harmonics, showing that a high-energy bunch of photons, up to the X-ray-energy region, with coherence typical of laser radiation and time duration comparable to or shorter than the exciting pulses, can be generated. [ABSTRACT FROM AUTHOR]

The driving force of a charge density wave (CDW) transition in quasi-two dimensional systems is still debated, while being crucial in understanding electronic correlation in such materials. Here we use femtosecond time- and angle-resolved photoemission spectroscopy combined with computational methods to investigate the coherent lattice dynamics of a prototypical CDW system. The photo-induced temporal evolution of the periodic lattice distortion associated with the amplitude mode reveals the dynamics of the free energy functional governing the order parameter. Our approach establishes that optically-induced screening rather than CDW melting at the electronic level leads to a transiently modified potential which explains the anharmonic behaviour of the amplitude mode and discloses the structural origin of the symmetry-breaking phase transition. The charge density wave (CDW) formation mechanisms in 2D and quasi-2D systems are still highly debated. Here, the authors combine time-resolved ARPES and ab initio calculations to map the free energy functional in the prototypical CDW compound 1T-TaSe2 concluding that the CDW state is driven by structural rather than electronic instabilities. [ABSTRACT FROM AUTHOR]

Presents a comprehensive theoretical and experimental study on cascaded second-order nonlinearity mode locking, a passive mode-locking technique. Functions of the mode-locking technique; Conversion of the nonlinear phase shift the originates in the nonlinear crystal; Analysis of the effects of group velocity mismatch and the limitations.

We present a modification of transient differential transmission spectroscopy, where the first excited state S1 is re-excited via a second laser pulse towards a higher lying state Sn. The dynamics of the relaxation of this state Sn as well as the kinetics of the states created from Sn is revealed by a broad-band probe pulse.We find an enhanced charge carrier generation from a higher lying excited state Sn. The push and probe durations below 20 fs allow the time resolution of the ultrafast relaxation of the Sn state and enables us to identify the two main contributions to enhanced charge generation from Sn, energy migration towards quenching sites and exciton dissociation during vibrational relaxation. [Copyright &y& Elsevier]

The transient photoinduced transmission of quinquethiophene-S,S-dioxide in solution is reported. Stimulated emission is observed in the viscous solvent, but quenched in polar and nonpolar low viscosity solvents. The lifetime of the photoexcited state changes of more than one order of magnitude depending on the solvent properties, pointing out conformational effects. Low-energy coherent transient is observed and assigned to real time conformational dynamics. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents the transverse effects in a Nd:YVO[sub 4] microchip solid-state laser due to gain-guiding. Role of transverse modulation of the gain profile and detuning in controlling spatial and spectral properties; Function of the pump beam dimension; Use of the Maxwell-Bloch equations to interpret laser behavior.

Describes the passive mode-locking of a cw diode-pumped Nd:YAG laser using the nonlinear mirror technique. Composition of the nonlinear mirror; Production of nearly transform-limited pulses by the laser; Ability of the mode-locking to self-start under optimized conditions.

Non‐linear excitation microscopy offers several advantages for in‐vivo imaging compared to conventional confocal techniques. However, tissue penetration can still be an issue due to scattering and spherical aberrations induced on focused beams by the tissue. The use of low numerical aperture objectives to pass through the outer layers of the skin, together with high dioptric power microlenses implanted in‐vivo close to the observation volume, can be beneficial to the reduction of optical aberrations. Here, Fibroblast cell culture plano‐convex microlenses to be used for non‐linear imaging of biological tissue are developed and tested. The microlenses can be used as single lenses or multiplexed in an array. A thorough test of the lenses wavefront is reported together with the modulation transfer function and wavefront profile. Magnified fluorescence images can be retrieved through the microlenses coupled to commercial confocal and two‐photon excitation scanning microscopes. The signal‐to‐noise ratio of the images is not substantially affected by the use of the microlenses and the magnification can be adjusted by changing the relative position of the microlens array to the microscope objective and the immersion medium. These results are opening the way to the application of implanted micro‐optics for optical in‐vivo inspection of biological processes. [ABSTRACT FROM AUTHOR]

Aim: The purpose of this study is to identify factors associated with diagnostic stability of Bipolar Mood Disorder (BMD) with statistical and clinical interest. Methods: Retrospective cohort study, in which the medical records of 916 individuals admitted to Coimbra University Hospital, between 1989 and 2008 with first diagnostic of BMD, were analysed for the following characteristics: age, gender, occupation, educational level, age at first diagnostic, number and types of hospital admissions, presence of suicide attempts, pharmacological treatments, time between first diagnostic and the new one (Schizophrenia, Delusional Disorder or Dementia), type of cognitive impairment, assessment examinations (TC-CE and EEG) and presence of co-morbidities. The analysed sample was divided in two groups: one that kept the first diagnostic (BMD) and another that later received a different diagnostic. Diagnostic criteria according to International Classification of Diseases- 10th edition. Results: 4,7% of the total sample received a different diagnostic in a posterior assessment: 41,9% Schizophrenia, 4,7% Delusional Disorder and 53,5% Dementia. The factors were analyzed with traditional statistical methods and Mann-Whitney''s test. The authors found five main factors with statistical significance between the two groups, namely, age, age at first diagnostic, total number of admissions and number of admissions for maniac episodes, and educational level. Conclusions: The aim of the study was achieved. In clinical practice the reported characteristics must receive a special attention in patient''s assessment, in order to verify the diagnostic stability and eventual evolution to another diagnostic. [Copyright &y& Elsevier]

Deals with a study which aimed to evaluate the relative risk of developing ESRD in three generations of a cohort of 110 patients with biopsy-proven IgAN. Methodology used in the study; Results and conclusion.

Abstract. We report on a sub-10-fs optical parametric amplifier in the visible, using noncollinear phase matching in beta-barium borate, with a pulse compressor made exclusively of chirped dielectric mirrors. We employ mirrors of novel design, providing negative group delay dispersion for bandwidths of over 200 THz, up to the blue-green spectral region. The resulting setup, compact, easy to operate and reliable, is an ideal tool for ultrafast spectroscopy with extremely high time resolution. We use these pulses to observe in the time domain coherent oscillations in organic molecules with period as short as 16 fs. [ABSTRACT FROM AUTHOR]

Aim Selected patients with haemorrhoidal prolapse undergoing double stapled anopexy with the procedure for prolapse and haemorrhoids (PPH03) were studied. Method Between March 2007 and March 2010, 235 patients referred with haemorrhoids were included in the study. Patients with obstructed defaecation were excluded. At surgery intraoperative evaluation for double stapled anopexy was carried out based on the criteria of prolapse occupying half or more of the anal circumference and redundant prolapsed tissue determined by the circular anal dilator. Patients fulfilling these criteria were submitted for double stapled anopexy with the PPH03 stapler. All clinical and operative data were recorded in a prospectively maintained database. Results Among the 142 patients with haemorrhoidal prolapse having surgery 91 had a single and 51 a double stapled technique. The mean operative time was 34.8 min with no major or minor intraoperative complications. Recurrence at 48 months was 1.9% and the mean satisfaction score was 8.9. Conclusion The double stapled PPH03 technique in selected cases was as safe and effective as a single stapling technique with a lower incidence of recurrence over a medium-term follow-up. [ABSTRACT FROM AUTHOR]

Purpose: The objective of this study was to evaluate the mid-term results of a new technique for the arthroscopic repair of MPFL after an acute patellar dislocation (APD). Materials: The series included 17 patients (11 men and 6 women) with a first episode of acute patellar dislocation; treated over a period of 6 years. Re-dislocation, subjective symptoms and functional limitations were evaluated at an average follow-up of 2.2 years (1-5.5). The patients were evaluated with the Lysholm and the Kujala scoring systems. Results: At follow-up, no re-dislocation was reported. Only one patient referred an episode of patellar instability, without a distinct dislocation. The postoperative median Lysholm score was 90 (72-100). The median Kujala score was 92 (75-100). Fourteen out of 17 patients were able to return to sports at the same level as before. Conclusion: When the MPFL is avulsed from the patella, the proposed technique has the advantage of restoring tension of the ligament through reattachment at the patellar border with two trans-patellar sutures. The full-arthroscopic approach has the advantage of being less invasive and having a shorter recovery time. [ABSTRACT FROM AUTHOR]

Abstract: A photoinduced decrease of refractive index has been demonstrated in SiO2:SnO2 (15mol%) optical-grade glass ceramic, exposed to a 780nm wavelength, focused femtosecond laser radiation at 1kHz repetition rate. Exposition have been performed translating the sample perpendicularly to the laser beam at a constant velocity of 17μm/s, with energies ranging between 2 and 5μJ per pulse. The samples were fabricated by the sol–gel method, from 85mol% tetraetoxysilane and 15mol% dibutyl tin-diacetate, adding water to a solution of the precursors. Xerogel was produced by slowly evaporating the solvent for 2 weeks at 35°C. The final material was obtained heating in O2 the xerogel samples by a thermal ramp (4°C/h) up to 1050°C. Samples were then cut from the blocks with a diamond saw to 10×10×1mm3 and all the faces polished. A negative variation of the refractive index has been demonstrated in the irradiated zone (−3×10−4) measured by the prism coupling technique. Multimode waveguides at 633nm have been obtained exploiting a positive refractive index change at the boundaries of the irradiated zone. Raman spectra have been measured showing several broad bands centered at about 430, 800 and 1100cm−1, and with two peaks at 490 and 610cm−1, when exciting at 488nm. Strong red luminescence has also been observed when exciting at 633nm suggesting the creation of non-bridging oxygen defects in the silica-based glass. We proposed that the negative refractive index change in the irradiated zone is due to the amorphization of the nanocrystals, while further investigation is needed to fully understand the origin of the positive index change at the boundaries. [Copyright &y& Elsevier]

Photoinduced non-thermal phase transitions are new paradigms of exotic non-equilibrium physics of strongly correlated materials. An ultrashort optical pulse can drive the system to a new order through complex microscopic interactions that do not occur in the equilibrium state. Ultrafast spectroscopies are unique tools to reveal the underlying mechanisms of such transitions which lead to transient phases of matter. Yet, their individual specificities often do not provide an exhaustive picture of the physical problem. One effective solution to enhance their performance is the integration of different ultrafast techniques. This provides an opportunity to simultaneously probe physical phenomena from different perspectives while maintaining the same experimental conditions. In this context, we performed complementary experiments by combining time-resolved reflectivity and time and angle-resolved photoemission spectroscopy. We demonstrate the advantage of this combined approach by investigating the complex charge density wave (CDW) phase in 1T-TiSe2. Specifically, we show the key role of lattice degrees of freedom to establish and stabilize the CDW in this material. [ABSTRACT FROM AUTHOR]

Display technology requires full red, green, and blue electroluminescence colors in polymer light emitting diodes. For the realization of blue emission poly(fluorene)s (PFs) are possibly the most attractive class of materials. The color stability of poly(fluorene)s is, however, relatively poor. Introducing bulky side chains, such as oligo-phenyl dendrons is a promising method for improving the color stability of these materials.The present study deals with the photophysics of a dendronically substituted poly(fluorene) derivative. The excited state properties are investigated by means of photoinduced absorption (PA) techniques at either quasi steady-state conditions or with femtosecond time resolution. [Copyright &y& Elsevier]