C. Bao-Varela

Fabrication of Metal-on-Glass High-Pitch Adapters Between VLSI Electronics and Semiconductor Sensors by Laser Ablation

High Energy Physics experiments make extensive use of silicon sensors for tracking purposes. The high granularity of the modern detectors makes the connection between the segmented sensor channels and the readout electronics very complex. Furthermore, due to the mismatch between the detector pad pitch and the electronics a direct connection is not possible in most of the cases. A new method for the fabrication of pitch adapters is presented using metal-on-glass technology. In this new method the high-density metal traces are manufactured by means of laser ablation of the metal layer deposited on top of a glass substrate. This new procedure is faster, simpler and cheaper than photolithography for prototyping or low volume production. Different prototypes have been successfully manufactured and tested for electrical conductivity, bondability and metrology. Detectors have been assembled using these pitch adapters and tested in particle beams at CERN.

Polarization gating using cross-polarized wave generation with multicycle lasers to produce isolated attosecond pulses in overdense media

A method to generate a polarization gate for multicycle laser pulses is presented. We study the performance of a pulse with time-dependent polarization to produce a single attosecond pulse after its interaction with an overdense plasma. The polarization gate is generated through the use of cross-polarized wave generation in a single BaF2 crystal combined with a dispersive medium. Numerical simulations demonstrate that using the polarization gate, the number of pulses in the attosecond train can be reduced. With this method a single attosecond pulse can be isolated by filtering the high harmonic orders in the reflected spectrum. The dependence of the ellipticity curve on the dispersion introduced is studied as well as its influence in the size of the polarization gate.

Laser technique for the fabrication of blood vessels-like models for preclinical studies of pathologies under flow conditions

In this work a method for fabricating functionalized preclinical devices is presented. The manufacturing process combines a laser indirect writing technique to fabricate a soda-lime glass master and soft-lithography methods to obtain the final structure in polydimethylsiloxane (PDMS). The roughness of the device is modified in a controlled manner by applying a post-thermal treatment to the master, and thus devices with different roughness values are created. The PDMS devices are fully covered with human umbilical vein cells in a two-step process. In order to determine the most suitable device to perform bioassays, the cell attachment to the channel is evaluated with regards to the walls roughness when flow experiments are carried out.

Spatiotemporal polarization pattern obtained by interference in a single cross-polarized wave-generation crystal

The cross-polarized wave-generation (XPW) nonlinearity has become the standard solution for producing high-contrast pulses in the amplification chain of femtosecond high-power laser systems. These high-contrast pulses are essential for the study of laser–plasma interaction with solid targets, and therefore it is very important to advance our understanding of how XPW works. The BaF2 crystal is the most common solution for implementing this technique, but until now the theoretical models have focused on pulse propagation inside XPW crystals with long focal lengths in order to ensure a clean spatial profile. In this kind of situation, diffraction in the crystal can be neglected. In this paper, we present a 3D model of XPW that includes diffraction and dispersion by solving a nonlinear Schrodinger equation with short focal lengths. The model describes the creation of the orthogonal wave along the crystal, taking into account the spatiotemporal phases of the new contributions and the propagations of the fields inside the crystal. Using this model, we show that pulses with complex polarization in space and time can be produced for certain parameters (low energy and short focal lengths). The origin of these complex structures is described in terms of the interference between different contributions of the orthogonal wave inside the crystal.

Laser Micromachining and Characterization of Metal-on-Glass High Density Pitch Adapters

Pitch adapters (PAs) are passive electronic components widely used to adapt different pitches between silicon strip detectors and readout electronics. This paper presents an optimized process to fabricate high-density PAs using laser ablation of metal-on-glass layers. Minimum pitch sizes of 40 μm for the pads and 25 μm for the conductive traces were achieved. The resolution of the method allowed the cutting of traces as narrow as 15 μm. Different prototypes and small production series have been successfully manufactured and tested for electrical parameters, bondability, and metrology. Ageing tests were also performed to ensure long-term reliability. The production yield reached 80%. Fully functional particle detectors for high-energy physics have been assembled using these PAs, characterized and tested with lasers and radioactive sources.

Fabrication of high-density pitch adapters by laser ablation

High Energy Physics experiments make extensive use of micro-strip silicon sensors for tracking purposes. However, the high granularity of the modern detectors makes the connection between the segmented sensor channels and the readout electronics very complex. Enhancing the complexity, a direct connection is not possible in most of the cases due to the mismatch between the detector pad pitch and the electronics. A new method based on laser technology is presented for the fabrication of pitch adapters. In this new method the high-density metal traces are manufactured by means of laser ablation of the metal layer deposited on top of a substrate. Glass, Kapton and Silicon substrates were metal coated and tested for the fabrication of pitch adapters. Finally, a metal-on-glass prototype has been successfully manufactured and tested for electrical conductivity, bondability and metrology. Detectors have been assembled using this pitch adapters design and tested in particle beams at CERN.

Laser based fabrication of preclinical devices for fluidic experiments

Since some pathologies, such as cardiovascular or tumour diseases, have become some of the main causes of morbidity worldwide, a huge interest in the development of preclinical devices for their study has aroused during the past years. Their fabrication is a key factor for the study of these illnesses and it is directly linked with their pathological knowledge, early diagnosis and improvement of treatment.

The USC-OSA-EPS section activities in optics

The USC-OSA Student Chapter and USC-EPS Young Minds Section is a group financed by The Optical Society (OSA) and the European Physical Society (EPS). It is formed by PhD and degree students from the Universidade de Santiago de Compostela (USC) and one supervisor of the Faculty of Physics. Its main goal is to promote and diffuse Optics in the society. For this purpose, the group carries out several activities in the academic and non-academic community. The group is also committed to the professional development of our members and motivates the exposition of our work into the scientific community.

Fabrication and characterization of a cell electrostimulator device combining physical vapor deposition and laser ablation

In this work we present the process of fabrication and optimization of a prototype of a cell electrostimulator device for medical application combining physical vapor deposition and laser ablation. The fabrication of the first prototype begins with a deposition of a thin layer of 200 nm of aluminium on a borosilicate glass substrate using physical vapor deposition (PVD). In the second stage the geometry design of the electrostimulator is made in a CAD-like software available in a Nd:YVO4 Rofin Power line 20E, operating at the fundamental wavelength of 1064 nm and 20 ns pulse width. Choosing the proper laser parameters the negative of the electrostimulator desing is ablated. After that the glass is assembled between two polycarbonate sheets and a thick sheet of polydimethylsiloxane (PDMS). The PDMS sheet has a round hole in where cells are placed. There is also included a thin soda-lime silicate glass (100 μm) between the electrostimulator and the PMDS to prevent the cells for being in contact with the electric circuit. In order to control the electrical signal applied to the electrostimulator is used a digital I/O device from National Instruments (USB-6501) which provides 5 V at the output monitored by a software programmed in LabVIEW. Finally, the optical and electrical characterization of the cell electrostimulator device is presented.

Sol-Gel Glass Coating Synthesis for Different Applications: Active Gradient-Index Materials, Microlens Arrays and Biocompatible Channels

The intent of this chapter is to review the use of sol-gel processing of silica and silica-titania optical coatings in recent research by the authors in three different areas: the synthesis of active gradient-index (GRIN) materials by multilayer deposition of erbiumand ytterbiumdoped silica-titania films, the improvement of the optical and morphological qualities of microlens arrays fabricated by laser ablation and the functionalization of polydimethylsiloxane (PDMS) channel preclinical devices. Through the use of sol-gel, layers with specific properties can be produced. In this regard, undoped and erbiumand ytterbium-doped SiO 2 -TiO 2 films have been produced and characterized using atomic force microscopy (surface topography evaluation) and spectral ellipsometry (determination of optical constants, thickness and porosity of the films). In a second application, a silica sol has been synthesized to coat microlens arrays fabricated by laser ablation. The deposited layer reduces the surface roughness of the microlens array, which yields the improvement of the contrast and the homogeneity of the foci. Finally, PDMS channels fabricated with laser technologies and soft-lithography methods are coated with a sol-gel-derived silica film to avoid the degradation of the material with organic solvents, and their biocompatibility is studied.