Dewetting acrylic polymer films with water/propylene carbonate/surfactant mixtures - implications for cultural heritage conservation

The removal of hydrophobic polymer films from surfaces is one of the top priorities of modern conservation science. Nanostructured fluids containing water, good solvents for polymers, either immiscible or partially miscible with water, and surfactants have been used in the last decade to achieve controlled removal. The dewetting of the polymer film is often an essential step to achieve efficient removal; however, the role of the surfactant throughout the process is yet to be fully understood. We report on the dewetting of a methacrylate/acrylate copolymer film induced by a ternary mixture of water, propylene carbonate (PC) and C_9-11E₆, a nonionic alcohol ethoxylate surfactant. The fluid microstructure was characterised through small angle X-ray scattering and the interactions between the film and water, water/PC and water/PC/C_9-11E₆, were monitored through confocal laser-scanning microscopy (CLSM) and analised both from a thermodynamic and a kinetic point of view. The presence of a surfactant is a prerequisite to induce dewetting of μm-thick films at room temperature, but it is not a thermodynamic driver. The amphiphile lowers the interfacial energy between the phases and favors the loss of adhesion of the polymer on glass, decreasing, in turn, the activation energy barrier, which can be overcome by the thermal fluctuations of polymer film stability, initiating the dewetting process.

Note: Real-time monitoring via second-harmonic interferometry of a flow gas cell for laser wakefield acceleration

The use of a gas cell as a target for laser wakefield acceleration (LWFA) offers the possibility to obtain stable and manageable laser-plasma interaction process, a mandatory condition for practical applications of this emerging technique, especially in multi-stage accelerators. In order to obtain full control of the gas particle number density in the interaction region, thus allowing for a long term stable and manageable LWFA, real-time monitoring is necessary. In fact, the ideal gas law cannot be used to estimate the particle density inside the flow cell based on the preset backing pressure and the room temperature because the gas flow depends on several factors like tubing, regulators, and valves in the gas supply system, as well as vacuum chamber volume and vacuum pump speed/throughput. Here, second-harmonic interferometry is applied to measure the particle number density inside a flow gas cell designed for LWFA. The results demonstrate that real-time monitoring is achieved and that using low backing pressure gas (<1 bar) and different cell orifice diameters (<2 mm) it is possible to finely tune the number density up to the 10(19) cm(-3) range well suited for LWFA.

Investigation on target normal sheath acceleration through measurements of ions energy distribution

An experimental campaign aiming at investigating the ion acceleration mechanisms through laser-matter interaction in femtosecond domain has been carried out at the Intense Laser Irradiation Laboratory facility with a laser intensity of up to 2 × 10(19) W/cm(2). A Thomson parabola spectrometer was used to obtain the spectra of the ions of the different species accelerated. Here, we show the energy spectra of light-ions and we discuss their dependence on structural characteristics of the target and the role of surface and target bulk in the acceleration process.

Note: strain sensitivity comparison between fiber Bragg gratings inscribed on 125 and 80 micron cladding diameter fibers, case study on the solidification monitoring of a photo-curable resin

The influence of fiber Bragg grating diameter when measuring strain is investigated and quantified. Two fiber Bragg gratings with bare cladding diameter of 125 μm and 80 μm are produced by excimer laser irradiation through a phase mask, and are used to simultaneously monitor the Bragg wavelength shift due to the strain produced by the solidification of a photo-curable resin during light exposure. It is found that the ratio of the measured strains in the two fiber Bragg gratings is close to the inverse ratio of the fiber's cladding diameter. These results represent a direct simultaneous comparison between 125 μm and 80 μm diameter fiber Bragg grating strain sensors, and demonstrate the feasibility of strain measurements in photo-curable resins using bare 80 μm cladding diameter fiber Bragg gratings with an increased sensitivity and spatial resolution compared with standard 125 μm diameter fiber Bragg gratings.

Towards excimer-laser-based stereolithography: a rapid process to fabricate rigid biodegradable photopolymer scaffolds

We demonstrate high-resolution photocross-linking of biodegradable poly(propylene fumarate) (PPF) and diethyl fumarate (DEF) using UV excimer laser photocuring at 308 nm. The curing depth can be tuned in a micrometre range by adjusting the total energy dose (total fluence). Young's moduli of the scaffolds are found to be a few gigapascal, high enough to support bone formation. The results presented here demonstrate that the proposed technique is an excellent tool for the fabrication of stiff and biocompatible structures on a micrometre scale with defined patterns of high resolution in all three spatial dimensions. Using UV laser photocuring at 308 nm will significantly improve the speed of rapid prototyping of biocompatible and biodegradable polymer scaffolds and enables its production in a few seconds, providing high lateral and horizontal resolution. This short timescale is indeed a tremendous asset that will enable a more efficient translation of technology to clinical applications. Preliminary cell tests proved that PPF : DEF scaffolds produced by excimer laser photocuring are biocompatible and, therefore, are promising candidates to be applied in tissue engineering and regenerative medicine.

Temporal and spatial characterization of a pulsed gas jet by a compact high-speed high-sensitivity second-harmonic interferometer

A compact modular high-speed high-sensitivity second-harmonic interferometer is used to characterize a pulsed gas jet. The temporal evolution of the line-integrated gas density is measured with a resolution of 1 μs revealing detailed information on its dynamics. The actual radial gas density distribution in the jet is obtained applying the Abel's inversion method. The sensitivity of the interferometer is 1 mrad, and its robustness, compactness and modularity make the instrument suitable for practical application. Possible use of the instrument in monitoring cluster formation, and phase-dispersion microscopy is discussed.

Dynamic formation of a hot field reversed configuration with improved confinement by supersonic merging of two colliding high-β compact toroids

A hot stable field-reversed configuration (FRC) has been produced in the C-2 experiment by colliding and merging two high-β plasmoids preformed by the dynamic version of field-reversed θ-pinch technology. The merging process exhibits the highest poloidal flux amplification obtained in a magnetic confinement system (over tenfold increase). Most of the kinetic energy is converted into thermal energy with total temperature (T{i}+T{e}) exceeding 0.5 keV. The final FRC state exhibits a record FRC lifetime with flux confinement approaching classical values. These findings should have significant implications for fusion research and the physics of magnetic reconnection.

Electron density measurements of a field-reversed configuration plasma using a novel compact ultrastable second-harmonic interferometer

A compact high-sensitivity second-harmonic interferometer for line-integrated electron density measurements on a large plasma machine is presented. The device is based on a fiber coupled near-infrared continuous-wave Nd:YAG laser and is remotely controlled. The performances of the instrument are tested on the Irvine field-reversed configuration machine, and a sensitivity of few 10(14) cm(-2) in measuring line integrated electron density is demonstrated with a time resolution of a few microseconds. The interferometer is self calibrated, has an impressive stability, and it does not require any further alignment after proper installation. These features make this device a real turn-key system suitable for electron density measurement in large plasma machines.

Spectral redshift in harmonic generation from plasma dynamics in the laser focus

High-precision spectral measurements on the 9th harmonic generated in xenon gas are compared with calculations of the plasma dynamics resulting from multiphoton ionization in the laser focus. For the regime of 300 ps pulses and above-saturation intensities a novel mechanism producing redshifts in the harmonics is uncovered and explained. Ions play a double role: the nonlinear susceptibility of the ions is decisive for the harmonic intensity, while their mutual repulsion and the associated increase of the index of refraction is identified as the cause of the redshift.

High-order harmonic generation yielding tunable extreme-ultraviolet radiation of high spectral purity

Production of extreme-ultraviolet radiation by high-order harmonic generation is demonstrated to yield unprecedented spectral purity of lambda/Delta lambda=2.5 x 10(5) at wavelengths covering the entire range 40-100 nm. Tunability and sub-cm(-1) bandwidth of the harmonics are demonstrated in recordings of the He (1s4p) and Ar (3p(5)3d') resonance lines at 52.2 and 86.6 nm. Frequency shift of the harmonics due to chirp-induced phenomena are investigated and found to be small, resulting in a frequency accuracy of about 5 x 10(-7) in the domain of extreme-ultraviolet radiation.

[Validity of some urinary tests considered singly or in combination in the study of renal effects of cadmium]

A number of indicators of renal effect (N-acetyl-glucosaminidase, retinol binding protein, beta-2-microglobulin, albuminuria) were measured in 42 cadmium-exposed workers divided into 3 subgroups on the basis of the results of the last 10 years' biological monitoring (less than 3, 3-10, greater than 10 micrograms/l). An increase in the first three indicators was observed, particularly in the third subgroup, which, however, due to the wide dispersion of the values, was not statistically significant by the Kruskal-Wallis test. Taking the indicators singly, the marked increase in RBP and beta-2-microglobulin in the heavily exposed subjects was confirmed, along with an increasing sensitivity for NAG, while albuminuria levels were unchanged. Assessment of the "degree of association" of the altered tests demonstrated that the number and type of "association" varies between the subgroups in relation to the exposure conditions: in the first group there were no associations between the altered tests, whereas there were 2 duplicates in the second and 2 duplicates, 2 triplicates and 3 quadruplicates in the heavily exposed group. In the study of the renal effects of cadmium, it is therefore advisable to use several indicators and assess their behaviour both singly and combined, and also analyse the altered tests on the basis of the number and type of "association".