Bioceramics with porous microstructure has attracted intense attention in tissue engineering due to tissue growth facilitation in the human body. In the present work, a novel manufacturing process for producing hydroxyapatite (HA) aerogels with a high density shell inspired by human bone microstructure is proposed for bone tissue engineering applications. This method combines laser processing and traditional freeze casting, in which HA aerogel is prepared by freeze casting and aqueous suspension prior to laser processing of the aerogel surface with a focused CO 2 laser beam that forms a dense layer on top of the porous microstructure. Using the proposed method, HA aerogel with dense shell was successfully prepared with a microstructure similar to human bone. The effect of laser process parameters on the surface, cross-sectional morphology and microstructure was investigated in order to obtain optimum parameters and has a better understanding of the process. Low laser energy resulted in a fragile thin surface with defects and cracks due to the thermal stress induced by the laser processing. However, increasing the laser power generated a thicker dense layer on the surface, free of defects. The range of 40–45 W laser power, 5 mm/s scanning speed, spot size of 1 mm, and 50% overlap in laser scanning the surface yielded the best surface morphology and microstructure in our experiments.

Fresnel zone plates (FZPs) have been gaining a significant attention by industry due to their compact design and light weight. Different fabrication methods have been reported and used for their manufacture but they are relatively expensive. This research proposes a new low-cost one-step fabrication method that utilizes nanosecond laser selective oxidation of titanium coatings on glass substrates and thus to form titanium dioxide (TiO 2 ) nanoscale films with different thicknesses by controlling the laser fluence and the scanning speed. In this way, phase-shifting FZPs were manufactured, where the TiO 2 thin-films acted as a phase shifter for the reflected light, while the gain in phase depended on the film thickness. A model was created to analyze the performance of such FZPs based on the scalar theory. Finally, phase-shifting FZPs were fabricated for different operating wavelengths by varying the film thickness and a measurement setup was built to compare experimental and theoretical results. A good agreement between these results was achieved, and an FZP efficiency of 5.5% to 20.9% was obtained when varying the wavelength and the oxide thicknesses of the zones.

Reliability aspects are crucial for the success of every technology in industrial application. Regarding interconnect devices, several methods are applied to evaluate reliability of conductor paths like accelerated environmental tests. Especially, molded interconnect devices (MID), which enable numerous applications with three-dimensional (3D) circuitry on 3D shaped injection-molded thermoplastic parts are often under particular stress, e.g., as component of a housing. In this study, a new test method for evaluating the flexural fatigue strength of conductor paths produced by the laser-based LPKF-LDS ® technology is presented. For characterization of test samples, a test bench for flexural fatigue test was built up. A result of the flexural fatigue test is a characteristic Woehler curve of the metal layer system. Applying this new test method, essential influencing parameters on the reliability of MID under mechanical load can be identified. So, the metal layer system as well as the geometric parameters of the metal layer is crucial for the performance. Furthermore, test specimens are tested under different types of mechanical load, i.e., tensile stress and compressive stress. For a holistic view on reliability of MID, experimental results are discussed and supported by simulations. An important finding of the study is the advantage of nickel-free layer systems in contrast to the Cu/Ni/Au layer system, which is often used in MID technology.

Laser microprocessing is a very attractive option for a growing number of industrial applications due to its intrinsic characteristics, such as high flexibility and process control and also capabilities for noncontact processing of a wide range of materials. However, there are some constrains that limit the applications of this technology, i.e., taper angles on sidewalls, edge quality, geometrical accuracy, and achievable aspect ratios of produced structures. To address these process limitations, a new method for two-side laser processing is proposed in this research. The method is described with a special focus on key enabling technologies for achieving high accuracy and repeatability in two-side laser drilling. The pilot implementation of the proposed processing configuration and technologies is discussed together with an in situ, on-machine inspection procedure to verify the achievable positional and geometrical accuracy. It is demonstrated that alignment accuracy better than 10 μ m is achievable using this pilot two-side laser processing platform. In addition, the morphology of holes with circular and square cross sections produced with one-side laser drilling and the proposed method was compared in regard to achievable aspect ratios and holes' dimensional and geometrical accuracy and thus to make conclusions about its capabilities.

This paper reports the development of an original design of chip breaker in a metal-matrix polycrystalline diamond (MMPCD) insert brazed into a milling tool. The research entailed finite element (FE) design, laser simulation, laser fabrication, and machining tests. FE analysis was performed to evaluate the effectiveness of different designs of chip breaker, under specified conditions when milling aluminum alloy (Al A356). Then, the ablation performance of an MMPCD workpiece was characterized by ablating single trenches under different conditions. The profiles of the generated trenches were analyzed and fed into a simulation tool to examine the resultant thickness of ablated layers for different process conditions, and to predict the obtainable shape when ablating multilayers. Next, the geometry of the designated chip breaker was sliced into a number of layers to be ablated sequentially. Different ablation scenarios were experimentally investigated to identify the optimum processing conditions. The results showed that an ns laser utilized in a controllable manner successfully produced the necessary three-dimensional feature of an intricate chip breaker with high surface quality (Ra in the submicron range), tight dimensional accuracy (maximum dimensional error was less than 4%), and in an acceptable processing time (≈51 s). Finally, two different inserts brazed in milling tools, with and without the chip breaker, were tested in real milling trials. Superior performance of the insert with chip breaker was demonstrated by the curled chips formed and the significant reduction of obtained surface roughness compared to the surface produced by the insert without chip breaker.

The manufacture of micro–nano structures in transparent dielectrics is becoming increasingly important due to the applications in medical and biological sciences. The femtosecond pulsed laser, with its selectivity, high precision, and three-dimensional direct writing nature, is an ideal tool for this processing technology. In this paper, an improved model for the prediction of ablation crater shape and fluence threshold in femtosecond laser processing of fused silica is presented, in which self-trapping excitons and electrons' relaxation are involved to depict ionization process, Thornber's and Keldysh's models are employed to estimate ionization rate precisely, and a novel ablation criterion is proposed to judge ablation. Moreover, the relationship between the ablation fluence threshold and laser pulse duration is investigated with three different extrapolation methods. The results indicate that no matter which extrapolation method is employed, the ablation fluence thresholds predicted by the presented model agree with the published data.

We report on periodic, homogeneous nanoripples fabricated on stainless steel (SS), copper (Cu), and aluminum (Al) substrates using an ytterbium pulsed femtosecond laser. These structures called laser induced periodic surface structures (LIPSS) are processed at a relatively high-speed and over large areas. This paper investigates the effect of LIPSS on a wettability behavior of SS, Cu, and Al surfaces. It is shown that nanoripples significantly influenced the wettability character of these metals turning them from hydrophilic to hydrophobic behavior.

Laser surface melting is being increasingly used as a method of surface polishing steels and other alloys, but understanding the effect of this process on the microstructure and properties is still incomplete. This work experimentally explores several basic questions about how the surface microstructure and properties of S7 tool steel change during a pulsed laser micromelting (PLμM) process. Evaluations of the microstructure and hardness suggest that diffusion-controlled processes such as melt homogenization and surface back-tempering are relevant during rapid microscale laser melting and that the laser parameters and process planning contribute to determining the final surface hardness. The results also suggest that some influence can be exerted over the final hardness obtained from laser surface melting by changing the processing parameters.