Design and fabrication of polymeric micro-optical components using excimer laser ablation

Abstract

Numerical simulation was used to predict the profile of a three-dimensional aspherical microlens and a microprism array. Based on the simulated results, the desired micro-optical lens profile was obtained using excimer laser ablated polyimide. The simulation method applied to excimer laser ablation can significantly reduce the quantity of microablation experiments. Ablated microstructures with surface roughness R _a < 20 nm were successfully achieved for micro-optical components. The excimer laser ablation parameters included laser fluence, shot number, workstation velocity, and repetition rate. Numerical simulation can be applied to predict various profiles of microlens and microprism arrays with different dimensions, the desired geometries being formed by laser ablation.     

Sample preconcentration using ion-exchange polymer film for laser ablation sampling inductively coupled plasma atomic emission spectrometry

An efficient sample pretreatment/introduction technique for the inductively coupled plasma atomic emission spectrometry (ICP-AES) using ion exchange for analyte preconcentration and matrix separation and laser ablation sampling for sample introduction has been developed. Ammonium pyrrolidine dithiocarbamate (APDC)-polystyrene films are coated on glass plates for analyte preconcentration. Repetitive laser ablation sampling of the polymer film removes the ion-exchanged metal ions from the polymer film as fine particles for sample introduction into the ICP. After immersing the sample probe in a sample solution for 5 min, the ICP emission intensity for laser ablation of the polymer film is a few times larger than that after solution nebulization. The sample probe removes only a small fraction of the sample solution and, therefore, in principle, does not disturb the original solution significantly. Single-pulse laser ablation of the polymer film shows that the ion-exchanged metal ion concentration in the film reduces exponentially with the depth of the polymer film. Ion exchange to the polymer film is probably limited by the rate of metal ion diffusion into the film. Calibration curves for Cu, Hg, Pb, and Zn show linear dynamic range of ～1-2 orders of magnitude. The linear dynamic range for Cu increases to >3 orders of magnitude when using Pb as an internal standard. RSD of the ICP emission intensity is ～8%.     

High precision axial coordinate readout for an axial 3-D PET detector module using a wave length shifter strip matrix

We describe a novel method to extract the axial coordinate from a matrix of long axially oriented crystals, which is based on wavelength shifting (WLS) plastic strips. The method allows building compact 3-D axial gamma detector modules for PET scanners with excellent 3-D spatial, timing and energy resolution while keeping the number of readout channels reasonably low. A voxel resolution of about 10 mm³ is expected. We assess the performance of the method in two independent ways, using classical PMTs and G-APDs to read out the LYSO (LSO) scintillation crystals and the WLS strips. We observe yields in excess of 35 photoelectrons from the strips for a 511 keV gamma and reconstruct the axial coordinate with a precision of about 2.5 mm (FWHM).     

Overestimated diffusion coefficients for the prediction of worst case migration from PET: application to recycled PET and to functional barriers assessment

This paper defines parameters that can be used to predict worst‐case migration from recycled PET bottles, with and without a functional barrier. Starting with a set of diffusion coefficients determined in well‐defined experimental conditions (temperature, presence or not of a solvent, with and without swelling effect), empirical equations for the diffusion coefficient of a migrant or a pollutant in PET at 40°C are given as a function of its molecular weight. An equation is also derived for migration from PET into water. Surrogates representative of worst‐case migrants are identified and are discussed in terms of molecular weight, structure and interaction with the PET matrix. In the second part of the paper, the empirical equations have been used to simulate the migration from monolayer bottles and from multilayer bottles with different geometries of functional barrier, as a function of the pollutants' molecular weight. Since the diffusion coefficients are overestimated, the calculated migration is also overestimated, which provides a margin of safety. The advantage of the functional barrier technology is compared to the direct food contact route, as a function of food contact time. In the last part of the paper, the effect of testing temperature is investigated. Based on a literature survey, the activation energy of pollutants is shown to increase roughly with their molecular weights. A worst‐case activation energy of 80 kJ/mol is proposed, allowing extrapolation of migration data from a higher temperature (values calculated at 40°C or determined at 60°C) to room temperature. The possible use of this activation energy to design tests for functional barriers is discussed. Copyright © 2004 John Wiley & Sons, Ltd.     

Deposition of polymer bilayer configuration by pulsed laser ablation and its use for study of polymer-polymer interface

Thin films of polyphenylene sulphide (PPS) and polyethylene (PE) polymers have been deposited in a bilayer configuration using pulsed excimer laser ablation. Such bilayer specimens have been annealed at different temperatures, up to a maximum of 120°C, and for different time intervals, up to a maximum of 110 min, to investigate the evolution of the interface. By employing the technique of spectroscopic ellipsometry, the nature and the degree of thermally induced polymeric transport across the interface are brought out.