Pulse duration dependent optical nonlinearities of Bi2Se3 thin films.

Topological insulators, such as the Bi2Se3 material, exhibit significant optical nonlinearities. This work investigates the impact of the pulse duration on the nonlinear optical responses of Bi2Se3 layers. Scanning electron microscopy studies have been performed to reveal the crystalline structure of the samples. The nonlinear optical performance has been investigated for a wide range of pulse durations, from 400 fs to 10 ps, using 1030 nm laser excitation. The nonlinear absorption coefficients recorded in this study range from -1.45 x10-7 m/W to -4.86 x10-7 m/W. The influence of two different mechanisms on optical nonlinearities was observed and discussed. Identical experimental conditions have been employed throughout the studies allowing a direct comparison of the results.

A randomized controlled trial evaluating the short-term efficacy of a single-administration intramuscular injection with the fixed combination of thiocolchicoside-diclofenac versus diclofenac monotherapy in patients with acute moderate-to-severe low back pain.

BACKGROUND: Non-specific acute low back pain (LBP) is a common health problem that may be accompanied by muscle spasm and decreased mobility. The combination of non-steroidal anti-inflammatory drugs and muscle relaxants represents an advantageous therapeutic option, however, available data on their combined use are conflicting. This prospective, randomized, single-blind, two-parallel-group trial assessed the efficacy of a single intramuscular (IM) injection of the fixed-dose combination (FDC) diclofenac (75 mg)-thiocolchicoside (4 mg/4 ml) product (test treatment) compared to diclofenac (75 mg/3 ml) alone (reference treatment) for the symptomatic relief of acute LBP. Tolerability and safety were also assessed as secondary variables. METHODS: One hundred thirty-four patients were enrolled (safety population) and randomly allocated to the combination or single-agent regimen. Pain intensity and muscle spasm, assessed respectively by the patient-reported visual analogue scale and investigator-performed finger-to-floor distance test, were determined prior to the injection as well as 1 and 3 h post-injection in 123 patients (per-protocol population). The patients were blinded to treatment. Safety was assessed up to 24 h post-injection. RESULTS: The test treatment was superior in both alleviating the pain intensity and reducing the finger-to-floor distance at both 1 (p < 0.01 and p = 0.023 respectively) and 3 h post-injection (p < 0.01). A higher percentage of patients experienced > 30% reduction in pain intensity at 1 and 3 h with the test treatment (p = 0.037 and p < 0.01 respectively). The corresponding VAS (SD) scores for the test treatment group were at baseline, 1 and 3 h post-injection 72.03 (± 11.72), 45.37 (± 16.28) and 31.56 (± 15.08) respectively and for the reference treatment group 65.20 (± 12.16), 48.98 (± 18.76) and 44.52 (± 17.33) respectively. No adverse effects were reported with the combination treatment, whereas two patients treated with diclofenac reported dizziness. CONCLUSIONS: The FDC treatment is an effective and well-tolerated option for the symptomatic treatment of LBP. Clinical and patient-reported assessments confirmed that a single IM injection of FDC diclofenac-thiocolchicoside was more effective than diclofenac alone in conferring rapid and sustained improvement in mobility and pain intensity. TRIAL REGISTRATION: EudraCT No: 2017-004530-29 Available at https://eudract.ema.europa.eu/ Registered 04 Dec 2017.

(Super)gelators derived from push-pull chromophores: synthesis, gelling properties and second harmonic generation.

The present work takes advantage of the self-assembly process occurring along organogelation, to organize Second Harmonic Generation (SHG) active chromophores. To do so, three push-pull chromophores endowed with a dodecyl urea chain were synthesized and characterized. Their organogelating properties were studied in a wide range of solvents. Despite similar architectures, these derivatives exhibit very different gelling properties, from supergelation to the absence of gelling ability. The utilization of the Hansen solubility parameters allows for observing clear relationships between the gelled solvents and critical gelation concentrations. By evaporating the solvents from the organogels, xerogel materials were prepared and systematically studied by means of optical and electron microscopy as well as SHG microscopy. These studies demonstrate the critical role of the solvent over material structuring and allow generalizing the approach exploiting organogelation as a structuring tool to spontaneously organize push-pull chromophores into SHG-active materials.

Promoting Spontaneous Second Harmonic Generation through Organogelation.

An organogelator based on the Disperse Red nonlinear optical chromophore was synthesized according to a simple and efficient three-step procedure. The supramolecular gel organization leads to xerogels which display a spontaneous second harmonic generation (SHG) response without any need for preprocessing, and this SHG activity appears to be stable over several months. These findings, based on an intrinsic structural approach, are supported by favorable intermolecular supramolecular interactions, which promote a locally non-centrosymmetric NLO-active organization. This is in sharp contrast with most materials designed for SHG purposes, which generally require the use of expensive or heavy-to-handle external techniques for managing the dipoles' alignment.

Coumarin-Containing Polymers for High Density Non-Linear Optical Data Storage.

Optical data storage was performed with various thin polymer films containing coumarin-based derivatives and by using femtosecond laser pulses as well as two-photon absorption processes. Exploring the photodimerization attribute of coumarin derivatives and using appropriate irradiation wavelengths, recording/erasing processes could be carried out in the same area. Second harmonic generation microscopy was used to read the stored information.

Crystalline arrays of pairs of molecular rotors: correlated motion, rotational barriers, and space-inversion symmetry breaking due to conformational mutations.

The rod-like molecule bis((4-(4-pyridyl)ethynyl)bicyclo[2.2.2]oct-1-yl)buta-1,3-diyne, 1, contains two 1,4-bis(ethynyl)bicyclo[2.2.2]octane (BCO) chiral rotators linked by a diyne fragment and self-assembles in a one-dimensional, monoclinic C2/c centrosymmetric structure where two equilibrium positions with large occupancy imbalance (88% versus 12%) are identified on a single rotor site. Combining variable-temperature (70-300 K) proton spin-lattice relaxation, (1)H T1(-1), at two different (1)H Larmor frequencies (55 and 210 MHz) and DFT calculations of rotational barriers, we were able to assign two types of Brownian rotators with different activation energies, 1.85 and 6.1 kcal mol(-1), to the two (1)H spin-lattice relaxation processes on the single rotor site. On the basis of DFT calculations, the low-energy process has been assigned to adjacent rotors in a well-correlated synchronous motion, whereas the high-energy process is the manifestation of an abrupt change in their kinematics once two blades of adjacent rotors are seen to rub together. Although crystals of 1 should be second harmonic inactive, a large second-order optical response is recorded when the electric field oscillates in a direction parallel to the unique rotor axle director. We conclude that conformational mutations by torsional interconversion of the three blades of the BCO units break space-inversion symmetry in sequences of mutamers in dynamic equilibrium in the crystal in domains at a mesoscopic scale comparable with the wavelength of light used. A control experiment was performed with a crystalline film of a similar tetrayne molecule, 1,4-bis(3-((trimethylsilyl)ethynyl)bicyclo[1.1.1]pent-1-yl)buta-1,3-diyne, whose bicyclopentane units can rotate but are achiral and produce no second-order optical response.

Image storage in coumarin-based copolymer thin films by photoinduced dimerization.

We report a technique to encode grayscale digital images in thin films composed of copolymers containing coumarins. A nonlinear microscopy setup was implemented and two nonlinear optical processes were used to store and read information. A third-order process (two-photon absorption) was used to photoinduce a controlled dimer-to-monomer ratio within a defined tiny volume in the material, which corresponds to each recorded bit of data. Moreover, a second-order process (second-harmonic generation) was used to read the stored information, which has been found to be highly dependent upon the monomer-to-dimer ratio.

Nonlinear absorption reversing between an electroactive ligand and its metal complexes.

We present the nonlinear absorption investigation of an electroactive ligand and two ruthenium and iron metal complexes under 532 nm, 30 ps laser excitation, by the "open aperture" Z-scan technique. Significant nonlinear optical parameters have in all cases been measured, while the nonlinear attribute has been found to change from saturable to reverse saturable absorption between the initial ligand and its complexes.

Reversible two-photon optical data storage in coumarin-based copolymers.

A functionalized polymer film allowing for a complete and straightforward second-harmonic generation (SHG)-assisted high-contrast writing-reading-erasing-writing sequence is proposed. The whole process is supported by the reversible photoinduced dimerization of a coumarin chromophore and enables efficient optical data storage that can be detected only by SHG imaging.

Giant ultrafast optical nonlinearities of annealed Sb2Te3 layers.

The optimization of thin Sb2Te3 films in order to obtain giant ultrafast optical nonlinearities is reported. The ultrafast nonlinearities of the thin film layers are studied by the Z-scan technique. Giant saturable absorption is obtained, which is the highest ever reported, by means of the Z-scan technique.

Second- and third-order nonlinearities of novel push-pull azobenzene polymers.

In this work, the second- and third-order nonlinear optical response of spin-deposited thin films of three different push-pull side chain azobenzene polymers is investigated by the second- and third-harmonic Maker fringes techniques using 30 ps laser pulses at a fundamental wavelength of 1064 nm. Measurements were carried out before and after aligning the chromophores by corona poling of the films, while different polarization configurations have been utilized. Strong dependence of the response upon the structure of the systems has been found, which is related to the different charge transfer within the molecules. The reported findings are compared with already published results.