Surface texturing by pulsed Nd:YAG laser Vilhena, L.M.; Sedlaček, M.; Podgornik, B. ...
Tribology international,
10/2009, Letnik:
42, Številka:
10
Journal Article, Conference Proceeding
Recenzirano
Introducing specific textures on a tribological surface can contribute to friction reduction in sliding contacts. In the present paper, a pulsed Nd:YAG laser emitting at 1064
nm, was used against ...100Cr6 steel samples in order to produce well-defined surface micro-pores, which can act as lubricant reservoirs, micro-hydrodynamic bearings as well as traps for wear debris. Due to the high flexibility of the laser system, structural features such as shape, size, density and depth can be varied easily by changing the laser parameters. To optimize the parameters of the laser surface texturing process, an investigation was performed using different pulse numbers, various pulse energies and two different modes (single- and multi-mode). The microtextures were characterized with optical microscopy, scanning electron microscopy (SEM) and by topography techniques. The relationship between the laser processing parameters and qualitative and quantitative profile of the micro-pores was studied. Tribological testing of laser textured surfaces was performed in a low frequency–long displacement reciprocating sliding wear tester under boundary lubrication and results compared to un-textured case. Tribological comparison of textured, textured and lapped, and untextured surfaces shows only minimal influence of texturing for contact conditions investigated.
We present a fast, displacement-measuring, single-pass, two-detector homodyne quadrature laser interferometer and compare its performance with an arm-compensated, proportional, ...integral-derivative-controlled Michelson interferometer. Special attention is given to the extension of the dynamic range. The wide dynamic range is achieved by an accurate fringe subdivision based on an enhanced ellipse-specific fitting of the scattered Lissajous curve and by increasing the total displacement using the quadrature-detection technique. The common periodic deviations, i.e., the unequal AC amplitudes, the DC offsets, and the lack of quadrature are determined and reduced by data processing based on an ellipse-specific, least-squares fitting to obtain nanometric accuracy. The performance of the described interferometer is demonstrated through the measurement of high-amplitude and high-frequency laser-induced ultrasound.
Pteropods are a group of holoplanktonic gastropods for which global biomass distribution patterns remain poorly described. The aim of this study was to collect and synthesise existing pteropod ...(Gymnosomata, Thecosomata and Pseudothecosomata) abundance and biomass data, in order to evaluate the global distribution of pteropod carbon biomass, with a particular emphasis on temporal and spatial patterns. We collected 25 939 data points from several online databases and 41 scientific articles. These data points corresponded to observations from 15 134 stations, where 93% of observations were of shelled pteropods (Thecosomata) and 7% of non-shelled pteropods (Gymnosomata). The biomass data has been gridded onto a 360 × 180° grid, with a vertical resolution of 33 depth levels. Both the raw data file and the gridded data in NetCDF format can be downloaded from PANGAEA, doi:10.1594/PANGAEA.777387. Data were collected between 1950–2010, with sampling depths ranging from 0–2000 m. Pteropod biomass data was either extracted directly or derived through converting abundance to biomass with pteropod-specific length to carbon biomass conversion algorithms. In the Northern Hemisphere (NH), the data were distributed quite evenly throughout the year, whereas sampling in the Southern Hemisphere (SH) was biased towards winter and summer values. 86% of all biomass values were located in the NH, most (37%) within the latitudinal band of 30–60° N. The range of global biomass values spanned over four orders of magnitude, with mean and median (non-zero) biomass values of 4.6 mg C m−3 (SD = 62.5) and 0.015 mg C m−3, respectively. The highest mean biomass was located in the SH within the 70–80° S latitudinal band (39.71 mg C m−3, SD = 93.00), while the highest median biomass was in the NH, between 40–50° S (0.06 mg C m−3, SD = 79.94). Shelled pteropods constituted a mean global carbonate biomass of 23.17 mg CaCO3 m−3 (based on non-zero records). Total biomass values were lowest in the equatorial regions and equally high at both poles. Pteropods were found at least to depths of 1000 m, with the highest biomass values located in the surface layer (0–10 m) and gradually decreasing with depth, with values in excess of 100 mg C m−3 only found above 200 m depth. Tropical species tended to concentrate at greater depths than temperate or high-latitude species. Global biomass levels in the NH were relatively invariant over the seasonal cycle, but more seasonally variable in the SH. The collected database provides a valuable tool for modellers for the study of marine ecosystem processes and global biogeochemical cycles. By extrapolating regional biomass to a global scale, we established global pteropod biomass to add up to 500 Tg C.
Recent advances in optodynamics Možina, J.; Diaci, J.
Applied physics. B, Lasers and optics,
11/2011, Letnik:
105, Številka:
3
Journal Article
Recenzirano
The term optodynamics has been introduced to describe a wide range of optically induced dynamic phenomena, which play an important role in laser–material processes as well as in laser-assisted ...medical applications. In view of laser material processing, a laser beam is not only considered as a tool, but also as a generator of information about the material’s transformation. The information is retained and conveyed by different kinds of optically induced mechanical motions, such as shock, acoustic and ultrasound waves, and cavitation bubbles. Special emphasis is given to the recent investigations of linear momentum transformation during the laser–material interaction and to the on-line monitoring of laser material processing.
In this investigation, we used high-speed shadow photography to observe fast optodynamic phenomena such as shock waves and the ablation of flat metal surfaces. These phenomena were induced in air by ...a Q-switched Nd:YAG laser (
λ
= 1,064 nm) with a pulse duration of 4 ns and an excitation pulse energy between 10 and 55 mJ. For a good spatial resolution of the shadowgraphs, we used short illumination pulses (30 ps) from a frequency-doubled Nd:YAG laser (
λ
= 532 nm). Using the shadowgraphs of the shock wave expansion into a half-space, we measured the optodynamic energy conversion efficiency, defined as the ratio between the mechanical energy of the shock wave and the excitation pulse energy. This efficiency increases with an increasing excitation pulse energy. We also present the characteristic shadowgraphs of the ablation of a black-painted metal surface, where the macroscopic material particles are clearly visible. They follow the shock wave and eventually overtake it. As a result, the shape of the shock wave, which normally expands concentrically into the half-space, has an altered form. The presented results reveal the phenomenon of the laser ablation of coated metal surfaces.
Real-time 3D visualization of the breathing displacements can be a useful diagnostic tool in order to immediately observe the most active regions on the thoraco-abdominal surface. The developed ...method is capable of separating non-relevant torso movement and deformations from the deformations that are solely related to breathing. This makes it possible to visualize only the breathing displacements. The system is based on the structured laser triangulation principle, with simultaneous spatial and color data acquisition of the thoraco-abdominal region. Based on the tracking of the attached passive markers, the torso movement and deformation is compensated using rigid and non-rigid transformation models on the three-dimensional (3D) data. The total time of 3D data processing together with visualization equals 20 ms per cycle.In vitro verification of the rigid movement extraction was performed using the iterative closest point algorithm as a reference. Furthermore, a volumetric evaluation on a live subject was performed to establish the accuracy of the rigid and non-rigid model. The root mean square deviation between the measured and the reference volumes shows an error of ±0.08 dm(3) for rigid movement extraction. Similarly, the error was calculated to be ±0.02 dm(3) for torsional deformation extraction and ±0.11 dm(3) for lateral bending deformation extraction. The results confirm that during the torso movement and deformation, the proposed method is sufficiently accurate to visualize only the displacements related to breathing. The method can be used, for example, during the breathing exercise on an indoor bicycle or a treadmill.
For quality control in high volume manufacturing of thin layers and for tracking of physical and chemical processes, ellipsometry is a common measurement technology. For such kinds of applications we ...present a novel approach of fast ellipsometric measurements. Instead of a conventional setup that uses a standard photo-elastic modulator, we use a 92 kHz Single Crystal Photo-Elastic Modulator (SCPEM), which is a LiTaO3 crystal with a size of 28 × 9 × 4 mm. This small, simple, and cost-effective solution also offers the advantage of direct control of the retardation via the current amplitude, which is important for repeatability of the measurements. Instead of a Lock-In Amplifier, an automated digital processing based on a fast analog to digital converter controlled by a highly flexible Field Programmable Gate Array is used. This and the extremely compact and efficient polarization modulation allow fast ellipsometric testing where the upper limit of measurement rates is mainly limited by the desired accuracy and repeatability of the measurements. The standard deviation that is related to the repeatability +/-0.002° for dielectric layers can be easily reached.
The transmittance of a transparent plate is theoretically and experimentally investigated, taking into account Fabry–Perot effects due to Fresnel reflections of a Gaussian beam on the boundaries of a ...plate. On the basis of these theoretical and experimental predictions, we present the application of a variable laser attenuator based on a thin transparent plate and a temperature regulation. Here, the absorption of the laser energy in the plate should be as low as possible, and its transmittance is changed by the interference due to the different thicknesses and refractive indices for the different temperatures of the plate. Therefore, such an attenuator can be used for a broad range of wavelengths and high-energy laser applications.
We present a new optodynamic experimental technique to measure the linear momentum obtained by a rod during a nanosecond laser pulse ablation of the rod’s front face on the basis of the displacement ...due to an ultrasonic wave reflection at its rear end. With the help of a simple theory, we explained the step-like motion of the rod’s free end. This theory conforms well with the general shape of the measured displacement history curve. The acquired momentum can be directly estimated by measuring the height of a step from the step-like motion of the rod’s end. Measurements based on an arm-compensated Michelson interferometer also enabled us to follow the attenuation of an ultrasonic wave and so to determine the characteristic attenuation time. This quantity plays a major role in the transfer of linear momentum from within the initial ultrasonic wave to the final net uniform motion of the specimen.
We examine the effects of the synchronized delivery of multiple Er:YAG-laser pulses during vapor-bubble oscillations into water. For this purpose, we used a laser beam transmission probe that enables ...monitoring of the bubble’s dynamics from a single shot. To overcome the main drawbacks of this technique, we propose and develop an appropriate and robust calibration by simultaneous employment of shadow photography. By using the developed experimental method, we show that the resonance effect is obtained when the second laser pulse is delivered at the end or slightly after the first bubble’s collapse. In this case, the resonance effect increases the mechanical energy of the secondary bubble’s oscillations and prolongs their duration. The presented laser method for synchronized delivery of Er:YAG-laser pulses during bubble oscillations has great potential for further improvement of laser endodontic treatment, especially upon their safety and efficiency.
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