Picosecond laser machined designed patterns with anti-ice effect

Micromachining using ultra short laser pulses (USLP) has evolved over the past years as a versatile tool for introducing functional features in surfaces at a micrometric and even at a sub wavelength scale. Being able to control the surface topography at this level provides a method to change the wetting behavior of a great number of materials. In most cases, when a surface has a natural tendency to be wetted (high surface energy), increasing its roughness will increase the spreading of water over it, and when it is naturally hydrophobic this roughness can dramatically enhance the water repellency. In this study, anti-ice properties of water repellent laser machined materials are investigated. Therefore, a stainless steel substrate (AISI 304L) has been textured with regular hatched patterns, using UV and green laser pulses of 6.7ps. In order to decrease the surface energy, a thin hydrophobic\ud coating has been applied on top of these structures. Super-hydrophobic state has been reached for many of the samples, and small hysteresis values have been measured to confirm the socalled, self-cleaning, or “lotus effect” properties of the engineered surfaces

Determination of Trace Silicone Contamination on Composites by Quantitative XPS and LIBS

Surface treatment and surface characterization techniques are critical to ensure that adherends are chemically activated and free of contaminants prior to adhesive bonding. Silicone contamination from mold-release agents and other sources can interfere with interfacial bonding, decreasing the durability and performance of bonded composite structures. Tools and methods are needed that can be used in a production environment to reliably detect low levels of contaminants in a rapid, simple, and cost-effective manner to improve bond reliability. In this work, surface characterization of carbon fiber reinforced polymer (CFRP) composites was performed using laser induced breakdown spectroscopy (LIBS) and the results were compared with those obtained from X-ray photoelectron spectroscopy (XPS). The objective was to investigate the ability to quantify the surface species measured by LIBS since it offers many advantages over XPS in terms of ease of use, sample preparation, and real-time results. The as-processed CFRP panels had trace surface silicone contamination from the fabrication process, the source of which was not investigated. The composites were laser treated at select average laser power levels, resulting in varying levels of contamination reduction. The Si atomic percentage measurements using XPS were conducted both before and after laser ablation. The XPS results were compared with those obtained from LIBS to assess the reliability of each technique for surface contaminant characterization. The results showed an excellent correlation in Si atomic concentration between the two techniques

Anisotropic conjugated polymer chain conformation tailors the energy migration in nanofibers

Conjugated polymers are complex multi-chromophore systems, with emission properties strongly dependent on the electronic energy transfer through active sub-units. Although the packing of the conjugated chains in the solid state is known to be a key factor to tailor the electronic energy transfer and the resulting optical properties, most of the current solution-based processing methods do not allow for effectively controlling the molecular order, thus making the full unveiling of energy transfer mechanisms very complex. Here we report on conjugated polymer fibers with tailored internal molecular order, leading to a significant enhancement of the emission quantum yield. Steady state and femtosecond time-resolved polarized spectroscopies evidence that excitation is directed toward those chromophores oriented along the fiber axis, on a typical timescale of picoseconds. These aligned and more extended chromophores, resulting from the high stretching rate and electric field applied during the fiber spinning process, lead to improved emission properties. Conjugated polymer fibers are relevant to develop optoelectronic plastic devices with enhanced and anisotropic properties.Comment: 43 pages, 15 figures, 1 table in Journal of the American Chemical Society, (2016

ULTRA SHORT PULSE LASER SURFACE MODIFICATION

ABSTRAC

High Gain Solid-State Amplifiers for Picosecond Pulses

We review solid-state laser amplifiers for generation of intense picosecond pulses, in various regimes from single shot to repetition rates of GHz. Such laser sources are becoming increasingly attractive for many industrial and scientific applications. In particular, we have exploited the technology of side-pumped grazing-incidence bounce amplifiers. Such amplifiers yield very high gain per pass, up to several thousands, and offer excellent beam quality preservation owing to the total reflection leading to left-right inversion. This technology allows the realization of compact, efficient and modular amplifiers, significantly simpler than, for example, cavity-based regenerative schemes. Starting from robust, low-power diode-pumped solid-state oscillators, using programmable pulse-pickers one can select either a single pulse or a properly shaped pulse train for further amplification and compensation of envelope distortions due to gain saturation. For single pulse amplification it is preferred to start with a relatively low-repetition-rate oscillator (< 100 MHz). Picosecond fiber oscillators are most promising in this respect. Using quasi-cw diode arrays as the pump source of Nd:YVO4 slab amplifier, starting from ≈ 1 nJ, 10-ps pulse seed, amplified pulse energy as high as 200 μJ at 1 kHz can be obtained. Efficient harmonic and traveling-wave parametric generation are readily achieved with such high pulse peak powers. Some other applications require instead the amplification of pulse trains, that can be conveniently extracted and amplified from a low-power oscillator at the desired repetition rate. For example, starting from a 20-mW, 5-GHz picosecond oscillator we amplified trains of few thousands of pulses up to 2 mJ with three slab amplifiers (as much as 300 mJ were achieved with two additional Nd:YAG flash-lamp-pumped post-amplifiers). Such pulse trains are very effective for synchronous pumping of optical parametric oscillators, lowering significantly their threshold with respect to the traveling-wave geometry. When multi-MHz picosecond pulses are required, cw diode arrays are chosen as pump sources for the slab amplifiers. An 8-W, 8-ps laser system has been demonstrated starting from a 50-mW cw oscillator, at 150 MHz. Owing to the effective gain shaping of the tightly pumped amplifier, no significant thermal distortion were detected, allowing nearly diffraction limited operation. Although high power picosecond oscillators have been demonstrated lately, this result is interesting since it suggests an alternative way for power-scaling of picosecond sources without pushing delicate intracavity components (such as semiconductor saturable absorbers) to the damage limit. Numerical models of the amplifiers and their dynamics are also reviewed. The effects of amplified spontaneous emission are discussed, as well as the most effective methods for its suppression

Effects of Different Laser Pulse Regimes (Nanosecond, Picosecond and Femtosecond) on the Ablation of Materials for Production of Nanoparticles in Liquid Solution

Ultra-short laser pulse interaction with materials has received much attention from researchers in micro- and nanomachining, especially for the generation of nanoparticles in liquid environments, because of the straightforward method and direct application for organic solvents. In addition, the colloidal nanoparticles produced by laser ablation have very high purity—they are free from surfactants and reaction products or by-products. In this chapter, nanosecond, picosecond and femtosecond laser pulse durations are compared in laser material processing. Due to the unique properties of the short and ultra-short laser pulse durations in material processing, they are more apparent in the production of precision material processing and generation of nanoparticles in liquid environments