Index of content:
Volume 28, Issue 4, November 2016
- Technical Articles
Conical microspike morphology formation and control on various metal surfaces using femtosecond laser pulse28(2016); http://dx.doi.org/10.2351/1.4954839View Description Hide Description
Formation of conical microspikes on various metal surfaces (316L stainless steel, Ti-6Al-4V, and Al5754) under femtosecond irradiation at high repetition rate is reported. Two types of microcone morphologies formed at these high repetition rates under high and low-fluence conditions were clearly distinguished. At low fluence (near the ablation thresholds), conical spikes with high aspect ratio and nonuniform distribution forms through random evolution. At high fluence, semiuniform conical spikes are formed through a simultaneous progressive evolution procedure with increasing the number of scans. Experimental results are presented showing the progression of random microspike formation to uniform microspikes as fluence increases and show how scan-speed affects the size of the spikes. Also, extraordinary absorption coefficient is measured for nonuniform conical spike covered 316L stainless steel formed under near threshold condition.
28(2016); http://dx.doi.org/10.2351/1.4954930View Description Hide Description
The photobiological safety of optical radiation emitted by image projectors, particularly of laser illuminated projectors (LIP), is addressed by the recently published product safety standard IEC 62471-5 [Photobiological Safety of Lamps and Lamp Systems—Part 5: Image Projectors (IEC, 2015)]. According to IEC 62471-5, the accessible emission is determined at a distance of 1 m from the projection lens. A classification framework is used to categorize projectors into risk groups (RG), indicating the degree of risk from potential optical radiation hazards to the eye and skin, ranging from the exempt risk group (RG0) to risk group 3 (RG3). According to IEC 62471-5, the highest classification permitted for consumer products is RG2. In this paper, a risk analysis for exposure to the emission of LIP classified as RG2, at distances less than 1 m is provided. The analysis shows that the risk for retinal injury associated with RG2 LIP or conventional projectors at distances less than 1 m can be considered as very low to negligible.
Multiple-beam laser patterning on aluminum oxide, zirconium oxide, and hydroxyapatite ceramic materials using a microlens array28(2016); http://dx.doi.org/10.2351/1.4955158View Description Hide Description
Microlens array patterning (MLAP) is a fabrication technology capable to generate simultaneously several thousands of features using a single laser beam. This is done by illuminating a microlens array (MLA) with a laser beam, consisting of several lenses with micrometer sizes which are arranged periodically. In this way, the resulting geometry on the irradiated material depends on the geometrical arrangement of the MLA. In this study, a nanosecond pulsed ultraviolet-laser is used for MLAP of aluminum oxide, zirconium oxide, and hydroxyapatite using an MLA with 150 μm lens pitch. It is shown that depending on the number of laser pulses and laser fluences, the pattern depth can be increased from less than one micrometer up to tens of micrometer. Different pattern geometries are also obtained by translating the ceramic material with X and Y stages. The MLAP speed is calculated and compared to direct laser writing using galvanometric scanning mirrors.
Effect of various dispersing agents on the stability of silver microparticle dispersion and the formulation of uniform silver film by laser melting28(2016); http://dx.doi.org/10.2351/1.4955011View Description Hide Description
We report on the substitution of silver nanoparticles' inks by silver microparticle dispersions as a material for the production of printable silver tracks by laser melting. This approach is promising, because it helps to reduce the production costs of such silver tracks. Though silver dispersions used as materials for laser melting mostly contain polyvinylpyrrolidone as a stabilizer, which results in the appearance of an undesired balling effect of silver during laser melting, the authors test stabilizers differing in molecular weight and functionality. The resulting differences in colloidal and physicochemical properties are investigated and related to the final silver layer quality.
28(2016); http://dx.doi.org/10.2351/1.4958971View Description Hide Description
In this work, Co–Cr–Mo powder is used to form laser clads on a γ-TiAl substrate. The oxidation behavior of Co-Cr-Mo alloys in air at 900 °C for 10 and 480 h has been studied. The results show that the uniform, fine, and defect-free microstructure of Co-Cr-Mo coating was prepared by laser cladding. The clad coating consisted of γ-Co (fcc), ε-Co (hcp), and Cr23C6. The specific mass gain as a function with the number of cycle plot was parabolic, which indicated that diffusion has controlled the oxidation process. At short time (10 h), the oxide scale formed on the surface was composed mainly of Cr2O3. With the increase in the duration of oxidation from 10 to 480 h, the thickness of the oxide film increased from about 1–1.5 to 6–6.5 μm. The analyses of oxide scale formed after long time (480 h) showed that layer II composed of CoCr2O4 formed on the Cr2O3 (layer I). When the thickness of the Cr2O3 layer increased, the defects such as porosity and microchannels were formed in oxide scale. Cobalt diffused from these defects to surface and with increasing the oxidation time, CoCr2O4 formed and covered the surface of oxide scale.