Silk Microlens Array

Optics that are capable of merging with biomaterials create a variety of opportunities for sensing disease, for therapeutics, and for augmenting brain-machine interface. The FDA has approved silk devices for sutures and reconstructive surgery. Recently, a silk product made from regenerated silk protein is FDA approved for orthopedic application, as the understanding of structure and processing technologies of silk fibroin has been improved. Here, we report a facile fabrication process to construct silk microlens array. The process includes preparation of regenerated silk solution and casting on a micropatterned poly(dimethylsiloxane) (PDMS) master. Due to the identical surface area of a unit patterned regime, the silk solution exhibits a partial wetting state in the vicinity of the silk solution–PDMS–vapor interface with same contact angle, and after drying, produces consistent radius of curvature within the microlens array. This in turn provides highly uniform focal length, focal spot diameter, and imaging performance of individual lens. Our results provide the foundation for biophotonic microlens adding new capabilities for implantable and degradable devices from regenerated silk protein.

Experimental research methods for CO2 laser cutting of HARDOX400 steel

he laser beam is a source of radiation with concentrated energy. The characteristics of the laser beam (spot energy, focal spot diameter, spot temperature) are aspects theoretically researched in this paper. The intensity of the laser beam transmitted to the surface of the part has a Gaussian shape. A CO2 laser was used in the processing of parts from a HARDOX400 steel sheet with a thickness g = 8mm. The values of the cutting parameters were established by sample tests. An experimental design with 27 observations was analyzed. The width of the cutting slot at the straight profile was measured. Physical quantities derived from the cutting parameters and working parameters used were calculated. Spot energy, cost and interaction time were determined and evaluated using the mathematical model given by GRAPH. The research findings show that the best values of the factors studied converge to average values in minimizing Kerf.

Numerical simulations in support of the design of an ultrasonic device for sub-assembly identification

In this paper, it is shown how numerical simulations can help designing an ultrasonic instrument operating in harsh conditions. To prevent fuel handling errors in sodium cooled fast reactors, the identification of fuel sub-assemblies using ultrasound is being investigated. It is based on the interpretation of a code (aligned notches) engraved on the sub-assembly head using an emitting/receiving ultrasonic sensor. This reading is performed in liquid sodium with high temperature (up to 600°C) transducers. A first experiment in liquid sodium demonstrated the feasibility of this method. The reading quality and robustness depend on various parameters related to the ultrasonic beam (spectral response, focal distance, focal spot size), the code geometry (especially the notches’ dimensions) and geometrical alignments. In order to avoid numerous experiments, two numerical models are developed. The first one is a finite element simulation of the sensor providing its radiated field. This model is validated with the well-known analytic solution of the Rayleigh integral; then it is applied to the sensor used in the sodium experiment. The focal distance and focal spot diameter are close to the expected values. The second simulation, using CIVA software, provides the ultrasonic scan of the code. The result is in good agreement with the sodium experiment and a first comparison with a water experiment shows that this numerical tool is relevant for easily taking into account misalignment and misorientation of the scan.

Role of the Features of Focused Laser Beam at Pulsed Laser Cutting

In this article investigation of the roles of two important factors of focused laser beam, the focal spot diameter and the Rayleigh length as determining variables of the beam quality were made. The equations of these two factors are based on those most commonly used in the literature. The exchange between three different beam quality numbers were shown. It is proven on the basis of the scientific literature, that the beam quality degrades compared to the original data given by the factory of laser. The causes of the beam quality degradation are lens aberrations in the optical path of the given laser, and the shifting of the beam propagation ratio (M2) to higher values. A new equation for estimation of the new, lowest value for M2 factor is presented, based on the comparison of the laser cut material thickness to the depth of focus, which is two times the Rayleigh length.

Reflection of intense laser light from microstructured targets as a potential diagnostic of laser focus and plasma temperature

The spatial-intensity profile of light reflected during the interaction of an intense laser pulse with a microstructured target is investigated experimentally and the potential to apply this as a diagnostic of the interaction physics is explored numerically. Diffraction and speckle patterns are measured in the specularly reflected light in the cases of targets with regular groove and needle-like structures, respectively, highlighting the potential to use this as a diagnostic of the evolving plasma surface. It is shown, via ray-tracing and numerical modelling, that for a laser focal spot diameter smaller than the periodicity of the target structure, the reflected light patterns can potentially be used to diagnose the degree of plasma expansion, and by extension the local plasma temperature, at the focus of the intense laser light. The reflected patterns could also be used to diagnose the size of the laser focal spot during a high-intensity interaction when using a regular structure with known spacing.

Numerical Simulations of Laser-Driven Cratering Experiments into Porous Graphite

We present the results of an experimental campaign conducted on the LULI2000 laser facility. Semi-infinite targets of a commercial grade of porous graphite were submitted to high-power laser irradiation inorder to generate craters. A 15 ns pulse duration was used along with a focal spot diameter of 900 µm to deliver energies up to 750 J. Numerical simulations of these shots have been performed following a specificmethodology which can be divided in three steps. Firstly, the mechanical loading induced by the laser iscalibrated by simulating the same shot on a thin aluminum target of which free surface velocity is measured byPDV and line-VISAR. Secondly, the same shot is performed on a thin graphite target to validate the materialmodel of graphite. Thirdly, the craterization shot on semi-infinite target is simulated. Numerical results arecompared to experimental measurements of craters obtained using an interferometric profilometer.

Laser-induced cratering of a 3DCC material at mesoscale: Experiments and simulations

This study concerns the damaging of a 3-Dimension Carbon/Carbon (3DCC) composite material under dynamic loading. Experiments were performed with a laser facility delivering energies between 13 and 40 J with 100 nanoseconds pulse duration. The focal spot diameter was 250 μm, leading to dynamic pressure up to 10 GPa. The focal spot being smaller than the size of the composite components, it allows us to study the dynamic behaviour of the material at mesoscopic scale. The dynamic process of this cratering is then investigated via 3D numerical simulations, and a Johnson-Holmquist model is proposed. It appears that comparison of simulations with experimental results is useful to identify the dynamic strength of individual components of composite materials.