Miroslav Liška

Thin Film Colorimetric Interferometry

Measurement technique for the study of very thin lubrication films down to one nanometer in a point contact between a steel ball and a transparent disc is used to explore the relationship between central and minimum film thickness and rolling speed at the interface between elastohydrodynamic and boundary lubrication for a series of lubricating fluids. This technique based on the colorimetric interferometry combines powerful film thickness mapping capabilities with high accuracy. It was confirmed that both hexadecane and mineral base oil obey the linear relationship between log central and minimum film thickness and log rolling speed predicted by elastohydrodynamic theory down to approximately one nanometer. Conversely, squalane and additive-treated mineral base oil showed film thickness enhancement at slow speeds caused by boundary layers formation within the lubricant film. Obtained experimental data was used for the determination of pressure-viscosity coefficients of test fluids. The measurement technique also enabled us to produce information about the influence of boundary layers on film thickness shape. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Seattle, Washington, October 1–4, 2000

Quantitative laser-induced breakdown spectroscopy analysis of calcified tissue samples

Ž. We report on the application of laser-induced breakdown spectroscopy LIBS to the analysis of important minerals and the accumulation of potentially toxic elements in calcified tissue, to trace e.g. the influence of environmental exposure, and other medical or biological factors. This theme was exemplified for quantitative Ž detection and mapping of Al, Pb and Sr in representative samples, including teeth first teeth of infants, second teeth .Ž

Optical trapping of Rayleigh particles using a Gaussian standing wave

Abstract We suggest a modification of a single beam optical trap which enables more effective axial trapping of nanoparticles. We employed interference of an incident wave and the wave which is reflected by the bottom of the trapping cell to create a standing wave trap. The scattering force is strongly suppressed for a highly reflective surface in this configuration and consequently the axial force is represented only by the axial gradient force. The main advantage of the standing wave set-up is that it produces a much stronger axial gradient force than the single beam trap, even without high N.A. focusing optics. The trap is less than four times deeper than the single beam one produced by a laser of the same power so that smaller particles could be trapped in the vicinity of an array of stable positions separated by λ/2 along the beam axis. Even the axial trap stiffness is several orders higher than in the single beam trap.

An Automatic System for Real-Time Evaluation of EHD Film Thickness and Shape Based on the Colorimetric Interferometry

This paper presents an automatic system for the real-time evaluation of elastohydrodynamic (EHD) film thickness and shape that incorporates an advanced experimental apparatus controlled by a computer with an extensive interferogram processing software. This software coordinates the data acquisition and instrument control and also provides real-time data processing and displaying. Film thickness evaluation technique based on the colorimetric interferometry successfully overcomes limitations of conventional optical interferometry. Colorimetric interferometry combining conventional chromatic interferometry with image processing and differential colorimetry gives instantaneous detailed information on EHD film thickness and shape for various regimes. This approach makes it possible to determine film thickness in the range of 1 to 800 nm with a resolution of about 1 nm. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Toronto, Ontario, Canada, Octob...

Simplified description of optical forces acting on a nanoparticle in the Gaussian standing wave

We study the axial force acting on dielectric spherical particles smaller than the trapping wavelength that are placed in the Gaussian standing wave. We derive analytical formulas for immersed particles with relative refractive indices close to unity and compare them with the numerical results obtained by generalized Lorenz-Mie theory (GLMT). We show that the axial optical force depends periodically on the particle size and that the equilibrium position of the particle alternates between the standing-wave antinodes and nodes. For certain particle sizes, gradient forces from the neighboring antinodes cancel each other and disable particle confinement. Using the GLMT we compare maximum axial trapping forces provided by the Gaussian standing-wave trap (SWT) and single-beam trap (SBT) as a function of particle size, refractive index, and beam waist size. We show that the SWT produces axial forces at least ten times stronger and permits particle confinement in a wider range of refractive indices and beam waists compared with those of the SBT.

Theoretical comparison of optical traps created by standing wave and single beam

Abstract We used generalised Lorenz–Mie scattering theory (GLMT) to compare submicron-sized particle optical trapping in a single focused beam and a standing wave. We focus especially on the study of maximal axial trapping force, minimal laser power necessary for confinement, axial trap position, and axial trap stiffness in dependency on trapped sphere radius, refractive index, and Gaussian beam waist size. In the single beam trap (SBT), the range of refractive indices which enable stable trapping depends strongly on the beam waist size (it grows with decreasing waist). On the contrary to the SBT, there are certain sphere sizes (non-trapping radii) that disable sphere confinement in standing wave trap (SWT) for arbitrary value of refractive index. For other sphere radii we show that the SWT enables confinement of high refractive index particle in wider laser beams and provides axial trap stiffness and maximal axial trapping force at least by two orders and one order bigger than in SBT, respectively.

Single-pulse laser-induced breakdown spectroscopy of samples submerged in water using a single-fibre light delivery system

Abstract Using a novel laser-induced breakdown spectroscopy set-up, accurate quantitative analysis of samples submerged in liquids has been demonstrated. The measurements were conducted using a single-fibre plus plastic tube assembly of 20 m length. This delivered the ablation laser light pulse and a buffer gas flow to the sample surface, and collected the light emitted by the micro-plasma for analysis. No distil optics were used at the sample end of the fibre. Argon, nitrogen and compressed air were used as buffer gases; while the rare gas resulted in slightly better signal-to-noise ratios, most analytical measurements were carried out with nitrogen for convenience and to provide comparability with in-air measurements. Detection limits and reproducibility were comparable to those achieved for the same samples placed in standard ambient air, with all other experimental conditions unchanged. In standard steel samples, detection limits of 310±45, 325±48 and 455±55 ppm for Cr, Mn and Si, respectively, could be achieved. Pattern recognition algorithms were used to identify, for classification, spectra of specimen submerged in turbid and non-transparent liquids.

Differential colorimetry: tool for evaluation of chromatic interference patterns

One of the oldest and simplest techniques for the determining the thickness of a thin transparent film is based on the evaluation of the interference colors produced by the film. Though its accuracy is limited and the technique itself has been superseded by many advanced techniques, it still plays an irreplaceable role in observing moving thin fluid lubricant films. A computer-aided system for the reconstructing the shape of a thin fluid film from chromatic interference fringes is presented conceptually, and parts of the system are demonstrated. Quasistatic fluid films were generated in an experimental apparatus operating as a twolayer Fizeau interferometer. Chromatic patterns produced by the Tolansky method were photographed and digitized. The CIELAB color difference equation was used for comparing interferograms with the digital color chart to determine the film thickness. Three-dimensional mesh surface plots of the film shape with high thickness resolution were generated using techniques of image processing and computer graphics. The limitations and accuracy of the proposed system are discussed, and its validity was checked by observing a lubricant’s ability to create a coherent film under various conditions.

Laser ablation for mineral analysis in the human body: integration of LIFS with LIBS

Trace mineral analysis of the body is invaluable in biology, medicine and dentistry when considering the role of mineral nutrition and metabolism in the context of maintaining human health. The presence of key elements in the body, such as boron, calcium, chromium, copper, iron, silicon and zinc are known to be of vital importance, but are often found to be present in inadequate quantity. In sharp contrast, the accumulation of other elements, such as aluminum, cadmium, lead and mercury is less favorable, since frequently these metals are already toxic at extremely low concentration levels, interfering with essential chemical processing of vitamins and minerals. Here we report on the application of laser-induced breakdown spectroscopy and laser-induced fluorescence spectroscopy to the analysis of important minerals and toxic elements within the body. Samples from different parts of the body have been studied, including specimens of skin tissue, finger nails and teeth. It is particularly noteworthy that specific sample preparation was not needed for any of these laser spectroscopic measurements, but that specimens could be used as taken from the source.

Experimental Study of Lubricant Film Thickness Behavior in the Vicinity of Real Asperities Passing through Lubricated Contact

This article presents an experimental study of the influence of real surface micro-geometry on the film thickness in a circular elastohydrodynamic (EHD) contact formed between a real, random, rough surface of steel ball and smooth glass disk. Phase shifting interferometry was used to measure in situ initial undeformed rough surface profiles, whereas thin film colorimetric interferometry provided accurate information about micro-EHD film thickness behavior over a wide range of rolling speeds. Two real roughness features were studied in detail—a 56-nm-high ridge and a 90-nm-deep groove, both transversely oriented to the direction of surface motion. It was shown that the ridge is heavily deformed in a loaded contact and its height increases with increasing rolling speed. The asperity tip film thickness behavior is quite similar to the contact average film thickness when the film thickness is higher than the undeformed ridge height. However, below this limit the film is thicker than what the EHD theory predicts. For the groove, a local reduction in film thickness at the leading edge was observed. When the groove is passing through the EHD conjunction, it maintains its undeformed shape. The behavior of both roughness features studied shows good agreement with previous experimental observations conducted using an artificially produced ridge and groove.