Study of Through-Hole Micro-Drilling in Sapphire by Means of Pulsed Bessel Beams

Ultrashort Bessel beams have been used in this work to study the response of a 430-m-thick monocrystalline sapphire sample to laser–matter interaction when injecting the beam orthogonally through the whole sample thickness. We show that with a 12 Bessel beam cone angle, we are able to internally modify the material and generate tailorable elongated microstructures while preventing the formation of surface cracks, even in the picosecond regime, contrary to what was previously reported in the literature. On the other hand, by means of Bessel beam machining combined with a trepanning technique where very high energy pulses are needed, we were able to generate 100 m diameter through-holes, eventually with negligible cracks and very low taper angles thanks to an optimization achieved by using a 60-m-thick layer of Kapton Polyimide removable tape

Fabrication of conductive micro electrodes in diamond bulk using pulsed Bessel beams

High-quality, in-bulk conductive graphitic microelectrodes are fabricated perpendicular to the surface of a 500 μm thick monocrystalline CVD diamond sample using pulsed Bessel beams. With a 12o cone angle beam, different pulse parameters are explored to optimize the graphitic wires which are written without sample translation. The quality of the electrodes and their electrical and structural properties have been analysed through currentvoltage characterization and micro-Raman spectroscopy. We have found that higher pulse duration favours better conductivity while pulse energy has an optimum value for the same. This trend is confirmed by the presence and the different amounts of graphitic-like sp2 bonded carbon revealed by the micro-Raman spectra in different configurations. Using suitable writing parameters, we are able to create electrodes with the resistivity of 0.04 Ω cm, which, to the best of our knowledge, is one of the lowest values ever reported in literature in the case of graphitic-like wires fabricated through laser micromachining

Evaluation of microscale crystallinity modification induced by laser writing on Mn3O4 thin films

Defining microstructures and managing local crystallinity allow the implementation of several functionalities in thin film technology. The use of ultrashort Bessel beams for bulk crystallinity modification has garnered considerable attention as a versatile technique for semiconductor materials, dielectrics, or metal oxide substrates. The aim of this work is the quantitative evaluation of the crystalline changes induced by ultrafast laser micromachining on manganese oxide thin films using micro-Raman spectroscopy. Pulsed Bessel beams featured by a 1 micrometer-sized central core are used to define structures with high spatial precision. The dispersion relation of Mn3O4 optical phonons is determined by considering the conjunction between X-ray diffraction characterization and the phonon localization model. The asymmetries in Raman spectra indicate phonon localization and enable a quantitative tool to determine the crystallite size at micrometer resolution. The results indicate that laser-writing is effective in modifying the low-crystallinity films locally, increasing crystallite sizes from ~8 nm up to 12 nm, and thus highlighting an interesting approach to evaluate laser-induced structural modifications on metal oxide thin films.Comment: 27 page

Study of Through-Hole Micro-Drilling in Sapphire by Means of Pulsed Bessel Beams

Ultrashort Bessel beams have been used in this work to study the response of a 430-\u3bcm-thick monocrystalline sapphire sample to laser\u2013matter interaction when injecting the beam orthogonally through the whole sample thickness. We show that with a 12\u25e6 Bessel beam cone angle, we are able to internally modify the material and generate tailorable elongated microstructures while preventing the formation of surface cracks, even in the picosecond regime, contrary to what was previously reported in the literature. On the other hand, by means of Bessel beam machining combined with a trepanning technique where very high energy pulses are needed, we were able to generate 100 \u3bcm diameter through-holes, eventually with negligible cracks and very low taper angles thanks to an optimization achieved by using a 60-\u3bcm-thick layer of Kapton Polyimide removable tape

Experimental investigations and finite element analysis of milling of Inconel 718 alloy

Super-alloys encompass great challenges in machinability. One such alloy of much interest in applications is Inconel 718. Its increased hardness, low thermal diffusivity and high temperature strength make it desirable for applications, at the same time rendering its machining a demanding task. Extensive studies have been performed on machinability of Inconel 718, from the turning process stand-point. However, there is found to be a comparative dearth of work on the milling process. Taking into account the versatility of end-milling within the family of milling processes and the research gap, we found that a parametric optimization (aimed at minimum machining forces) of end-milling would be a meaningful effort. An experiment was conducted to study conditions that would help us achieve the same. In our further quest for optimization, chip morphology studies using SEM occupied a special place. Bearing in mind immense prediction capabilities of computer simulations based on FEA available today, we attempted process replication of the experimental work. The significant cutting forces were chosen as the benchmark factor for this purpose and proper attention was given to validation of the FEM created. Such FEM holds promise of being resourceful to drive up efficiency, with consequent spill-over to the production line

Laser micromachining of diamond: A viable photonic and optofluidic platform

We describe how the ultrafast laser micromachining technique applied with different writing methods can be used for the creation of various building blocks essential for the realization of a photonic and optofluidic diamond platform. Waveguides, NV centers, conductive wires, microchannels and microholes can be obtained thanks to laser microfabrication with suitable pulse parameters, making use not only of standard Gaussian laser beams but also of non-diffracting Bessel beams, the latter especially in all those cases where single pass high aspect-ratio microstructures or ablated areas are needed