D. Bäuerle

Laser-induced surface patterning by means of microspheres

A regular lattice of SiO2 microspheres on a quartz support is used as a microlens array for laser-induced surface patterning of polyimide foils.

Rapid in-situ analysis of liquid steel by laser-induced breakdown spectroscopy☆

Abstract Laser-induced breakdown spectroscopy (LIBS) denotes a technique where a pulsed laser beam is used to ablate small amounts of the target material. The characteristic optical emission line intensities of the excited species in the laser-generated plasma allow a quantitative chemical analysis of the target material. LIBS is a fast, non-contact method allowing large working distances between the sample under investigation and the detection system. These properties make LIBS applicable to process control in metallurgy. We describe an apparatus designed for rapid in-situ analysis of solid and molten metals at variable distances of up to 1.5 m. A variable lens system allows compensation for varying positions of the liquid steel surface. The LIBS signal is guided by a fiber optic bundle of 12-m length to the spectrometer. Analysis of an elements concentration takes 7 s. Laboratory experiments using an induction furnace showed that the addition of admixtures to liquid steel results in rapid response of the system. Results including the in-situ monitoring of Cr, Cu, Mn and Ni within certain concentration ranges are presented (Cr: 0.11–13.8 wt.%; Cu: 0.044–0.54 wt.%; Mn: 1.38–2.5 wt.%; Ni: 0.049–5.92 wt.%).

Ar+ laser induced chemical vapor deposition of Si from SiH4

For the first time polycrystalline silicon has been grown by using the visible light of an Ar+ laser for pyrolytical decomposition of SiH4. With a laser irradiance of 3600 W/mm2 a deposition rate of 30 μm/s was obtained. The temperature dependence of the deposition rate was investigated. The kinetically controlled regime is characterized by an activation energy of 44±4 kcal/mole.

Adhesion and proliferation of human endothelial cells on photochemically modified polytetrafluoroethylene

We studied the adhesion and proliferation of human endothelial cells on photochemically modified polytetrafluoroethylene samples. The polymer surfaces were modified by exposure to the ultraviolet light of a Xe(2)(*)-excimer lamp at a wavelength of 172 nm in an ammonia atmosphere. Treatment times were between 10 and 20 min. The endothelial cell density was determined 1, 3 and 8 days after seeding by image analysis. Surface modification of the samples resulted in a significant increase in the number of adhering cells and in the formation of a confluent cell layer after 3-8 days. The results were comparable than those obtained on polystyrene Petri dishes, which are used as standard substrates in cell cultivation. Thus modified PTFE appears to be a promising material for the fabrication of artificial vascular prostheses coated with endothelial cells.

Influence of the beam spot size on ablation rates in pulsed‐laser processing

Ablation rates in pulsed‐laser processing depend heavily on the laser beam spot size. This has been observed for the first time for a number of different materials. Detailed investigations on this effect, performed by means of XeCl excimer‐laser radiation and the example of LiNbO3, are reported in this letter. With this material, the ablation rate at constant fluence saturates at laser beam spot sizes of 2w≳80 μm and increases by about a factor of 3 when 2w is decreased to 24 μm. The effect is interpreted as being due to changes in the material transport which depend on the size of the region being processed.

Laser induced chemical vapor deposition of carbon

Initial results on laser‐induced chemical vapor deposition using the visible radiation of an Ar+ laser are presented. Due to the smaller wavelength of Ar+ laser radiation in comparison to the infrared radiation of a CO2 laser used in earlier experiments, much finer patterns could be produced. The influence of laser irradiance on the deposition rate and widths of patterns was investigated.

Laser-induced formation and surface processing of High-Temperature superconductors

The use of lasers in the formation and surface processing of high-temperature superconductors (HTS) is reviewed. Presently, thin film fabrication by reactive laser sputtering, and surface patterning by laser-induced reduction/metallization and ablation are the most promising applications. The great majority of the investigations have been performed for Y-Ba-Cu-O.

Crystal structure and superconductivity in REBaSrCu3Ox

Abstract The preparation, crystal structure and physical properties of REBaSrCu 3 O x compounds have been studied (Re≡La, Pr, Nd, Sm, Eu, Gd, Dy, Y, Ho, Er, Tm, or Lu). These compounds are found to be superconducting with a transition temperature within the range 54 K ≤ T c ≤86 K, except for RE = Pr, which is semiconducting. The maximum transition temperature is observed with RE=Gd and Dy where the lattice structure changes from tetragonal to orthorhombic.

Particulates on pulsed-laser deposited YBaCuO films

Abstract Different types of particulates observed on high temperature superconducting YBaCuO films prepared by pulsed-laser deposition on MgO substrates are investigated as a function of deposition parameters and classified according to their size, shape, and chemical composition. Among the parameters studied in detail are the oxygen pressure, the substrate temperature, the laser energy, fluence, spot size, and the number of pulses. The interrelations between the different particulates, the ablation and deposition rates, the shape of the visible plasma plume, and the film properties have been investigated.

Excimer‐laser‐induced etching of ceramic PbTi1−xZrxO3

The etching of ceramic PbTi1−xZrxO3 (PZT) by XeCl excimer laser radiation has been investigated. In air, the threshold fluence for etching was about 2 J/cm2. At fluences of 10 J/cm2, etch rates of 0.1 μm/pulse were observed. The geometry of etched structures can readily be defined by choosing suitable experimental conditions, suggesting potential applications of this process to the production of devices.