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This paper presents a laser-based system for a local transformation of the magnetic properties in austenitic stainless steel. The process is applied to linear actuators with an integrated, in-axis position measurement where durability and high precision are needed. The developed system consists of a 400-W, single-mode fiber laser, the focusing optics, and a three-axis actuation system. An important feature is the optical feedback for the adaptive, high-speed (40 kHz) laser power regulation. The experimental results show that the optical feedback effectively compensates for the external disturbances, like an increased roughness and a gradual heat accumulation. The regulation decreases the dispersion of the magnetic signal’s response by more than 100% and shortens the transient time at the beginning of the inscription process from 100 to 15 ms.

Erbium:yttrium aluminum garnet laser cleaning is a promising technique in endodontic treatment. In our in vitro study, we measured the vapor-bubble dynamics in the root canal by using shadow photography. The canal model was made of a plastic cutout placed between two transparent glass plates. An artificial smear layer was applied to the glass to study cleaning efficiency. In our results, no shock waves have been observed, since the pulp-chamber dimensions have been in the same range as the maximum diameter of the vapor bubble. This leads to the conclusion that shock waves are not the main cleaning mechanism within our model. However, the cleaning effects are also visible in the regions significantly below the bubble. Therefore, it can be concluded that fluid flow induced by the bubble’s oscillations contributes significantly to the canal cleaning. We also proposed a simple theoretical model for cleaning efficiency and used it to evaluate the measured data.

The near-field, surface-displacement waveforms in plates are modeled using interwoven concepts of Greenʼs function formalism and streamlined Huygensʼ principle. Greenʼs functions resemble the building blocks of the sought displacement waveform, superimposed and weighted according to the simplified distribution. The approach incorporates an arbitrary circular spatial source distribution and an arbitrary circular spatial sensitivity in the area probed by the sensor. The displacement histories for uniform, Gaussian and annular normal-force source distributions and the uniform spatial sensor sensitivity are calculated, and the corresponding weight distributions are compared. To demonstrate the applicability of the developed scheme, measurements of laser ultrasound induced solely by the radiation pressure are compared with the calculated waveforms. The ultrasound is induced by laser pulse reflection from the mirror-surface of a glass plate. The measurements show excellent agreement not only with respect to various wave-arrivals but also in the shape of each arrival. Their shape depends on the beam profile of the excitation laser pulse and its corresponding spatial normal-force distribution. Valovne oblike pomikov površine plošč smo v bližnjem polju modelirali z uporabo prepletenih konceptov formalizma Greenovih funkcij ter dopolnjenega Huygensovega načela. Greenove funkcije, ki ustrezajo gradnikom iskanih valovnih oblik, so pri tem ustrezno utežene in superponirane glede na njihovo poenostavljeno porazdelitev. Ta pristop vključuje poljubno krožno prostorsko porazdelitev vira in poljubno krožno prostorsko občutljivost senzorja na merilnem območju. Izračunali smo valovne oblike za enakomerno, Gaussovo in kolobarno porazdelitev vira ter za enakomerno občutljivost senzorja, pri čemer smo ustrezne utežene porazdelitve med seboj primerjali. Kot demonstracija uporabnosti razvitega modela smo izračunane valovne oblike primerjali z meritvami laserskega ultrazvoka induciranega zgolj s sevalnim tlakom. Ultrazvok je bil sprožen z laserskim bliskom, ki se je odbil od zrcalne površine steklene plošče. Meritve kažejo na odlično ujemanje z modelom tako pri časih prihoda posameznih valov kot tudi pri njihovih oblikah. Slednje so odvisne od časovnega poteka vpadlega laserskega bliska ter od njegove prostorske porazdelitve.

In the study of ultrasound propagation in matter, displacement sensors are indispensable and of these, the most sensitive are piezoelectric sensors. In order to eliminate the intrinsic effects of the sensor from the measurements, the sensor has to be properly calibrated, which means that its transfer function has to be evaluated from a known sensor input signal and a measured sensor output signal. This has usually been done by comparing the sensor response signal to a known input signal, namely, an ultrasonic waveform, which can be theoretically calculated using mathematical models and numerical algorithms. Until now, the point-source-point-sensor model has been primarily used, while ultrasonic waves were induced mechanically either by a dropped ball or a capillary fracture. In this paper, a real-source-real-sensor model is presented. It provides a more faithful waveform construction and it enables the removal of the aperture effect from the calculated sensor transfer function, thus giving correct and universal sensor response characteristics. This was corroborated by high-frequency calibration measurements of the output signal of a Glaser-type conical sensor in two positions on both surfaces of a glass plate, while ultrasonic waves were induced by the radiation pressure of a nanosecond laser pulse. V prispevku je predstavljena kalibracija piezoelektričnega senzorja majhnih pomikov z ultrazvočnimi valovi, ki jih vzbudi svetlobni tlak laserskega bliska na površini steklene plošče. S primerjavo meritev in matematičnega modela širjenja ultrazvoka v trdni snovi je določena frekvenčna karakteristika senzorja pri višjih frekvencah kot doslej. Merjenje majhnih pomikov snovi je nepogrešljivo pri proučevanju širjenja mehanskega valovanja v snovi. Med vsemi senzorji so najbolj občutljivi tisti, ki delujejo z izkoriščanjem piezoelektričnega pojava, in so zato najbolj primerni za merjenje valovanj z majhno amplitudo pomika. Takšni senzorji so tako v uporabi v strojništvu, pri testiranjih ter v razvoju in raziskavah. Uporabljajo se pri meritvah akustične emisije in pri neporušnih preiskavah snovi, v mikroseizmologiji ter pri mnogih drugih aplikacijah ultrazvoka v snovi.

This article presents a new system for 3D foot-shape measurements during walking. It is based on the laser-triangulation, multiple-line-illumination and color-modulation techniques. It consists of a walking stage and four measuring modules that simultaneously acquire the foot shape from the top, bottom and side views. The measuring speed is 30 fps. Custom-developed software makes it possible to analyze the foot's dimensions at an arbitrary cross-section by means of the width, height, girth and section orientation. Six subjects were measured during bare and shod walking, and the bare foot and the outside dimensions of the footwear during the entire stance phase are presented. The relative measurement repeatability of a single subject is 0.5% for bare foot and 1% for shod foot. This means that it is possible to study the differences between various influences on the foot-shape dynamics, such as a bare/shod foot, different loading conditions and the shoe's stiffness condition.

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.

In this paper we report on a theoretical and experimental study of the steady-state response, transient response and efficiency of a thermal management system. We compare two alternative designs based on thermo-electric modules, the role of which is to control the temperature of the laser-diode pumping system for advanced fiber lasers. The performances of a standard pulse-width modulation controller and a variable-voltage controller were tested on a reference thermal management system. An experimental facility and a numerical model were set up, with the system response to various load conditions measured as well as numerically simulated. The results show that the design of the thermal management system based on the variable-voltage controller offers a significant performance advantage over the pulse-width modulation design.

Jedan od bitnih izazova u daljinskoj laserskoj 3D obradi (RL3DP) je postizanje visoke točnosti jer laser radi po rubovima predmeta koji obrađuje. Ovaj rad prikazuje novi RL3DP sustav s automatskom 3D nastavnom funkcionalnošću radi točnog i brzog određivanja prijenosa detektiranih rubova koje obrađuje robot sa 3D skenerom, fiber laserom i izvan aksijalno pozicioniranom kamerom. 3D skeniranje se bazira na laserskoj triangulaciji sa pilotskom laserskom trakom. Eksperimentalni rezultati pokazuju da sustav ima preciznost bolju od 70 μm i 120 μm u bočnom i vertikalnom smjeru u mjernom području od 100 × 100 mm. Vrijeme učenja je 30-puta kraće u odnosu na vizualni postupak. Stoga, takav sustav može značajno smanjiti troškove obrade sa modernim proizvodnim sistemima koji se moraju prilagođavati stalnim promjenama geometrije i funkcionalnosti proizvoda., One of the key challenges in robotic remote laser 3D processing (RL3DP) is to achieve high accuracy for the laser’s working trajectory relative to the features of the workpiece. This paper presents a novel RL3DP system with an automatic 3D teaching functionality for a precise and rapid determination of the working trajectory which comprises a robot manipulator, 3D scanning head, fibre laser and an off-axis positioned camera. The 3D measurement is based on laser triangulation with laser-stripe illumination using the laser’s pilot beam and scanning head. The experimental results show that the system has a precision better than 70 μm and 120 μm along lateral and vertical direction respectively inside the measuring range of 100 × 100 mm. The teaching time is 30-times shorter compared to a visual teaching procedure. Therefore, such a system can lead to large cost reductions for modern production lines that have constant changes to the products’ geometries and functionalities.

We report on the successful realization of a contactless, non-perturbing, displacement-measuring system for characterizing the surface roughness of polymer materials used in tribological applications. A single, time-dependent, scalar value, dubbed the collective micro-asperity deformation, is extracted from the normal-displacement measurements of normally loaded polymer samples. The displacement measurements with a sub-nanometer resolution are obtained with a homodyne quadrature laser interferometer. The measured collective micro-asperity deformation is critical for a determination of the real contact area and thus for the realistic contact conditions in tribological applications. The designed measuring system senses both the bulk creep as well as the micro-asperity creep occurring at the roughness peaks. The final results of our experimental measurements are three time-dependent values of the collective micro-asperity deformation for the three selected surface roughnesses. These values can be directly compared to theoretical deformation curves, which can be derived using existing real-contact-area models.

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 bubbleʼs 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 devel- oped 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 bubbleʼs collapse. In this case, the resonance effect increases the mechanical energy of the secondary bubbleʼs 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.

Optodynamic interaction between a laser pulse and the surface of an opaque, solid elastic object produces transient waves that propagate and reverberate within the object. They can be, in general, categorized into three distinctive types which are all formed through different mechanisms: ablation-induced waves, light-pressure-induced waves, and thermoelastic waves. In this paper, out-of-plane displacements of such waves are simulated at the epicentral position on the opposite side of an extended plane-parallel elastic plate. Wave propagation is mathematically described by Greenʼs transfer functions convolved with suitable time profiles of the incoming laser pulses. The simulated size of the circularly symmetric laser-illuminated area on the plate surface is varied to show the limit-to-limit transition of the displacement waveforms: from a 2D point source to an infinite 1D source. Optodinamska interakcija med laserskim bliskom in površino neprozornega trdnega elastičnega predmeta povzroči prehodne valove, ki se širijo in zvenijo znotraj predmeta. V splošnem se jih lahko razdeli na tri značilne vrste, ki se razlikujejo glede na mehanizem nastanka: ablacijsko inducirane valove, valove povzročene s svetlobnim tlakom in termoelastične valove. V tem članku so simulirani izvenravninski pomiki takih valov v epicentralnem položaju na nasprotni površini široke planparalelne elastične plošče. Širjenje valovanja se matematično opiše s konvolucijo Greenove prenosne funkcije z ustreznim časovnim potekom vpadlega laserskega bliska. Pri tem se simulirana velikost vpadnega območja krožno simetričnega laserskega bliska na površini plošče spreminja, s čimer je prikazan prehod valovnih oblik iz ene limite drugo: iz 2D točkastega vira v neskončen 1D vir.

We developed a method that accurately determines an unknown position of the high-intensity laser-pulse-material interaction site on the front side of a plate. It is based on interferometric measurements of a normal displacement at known positions on the plate’s rear side. The displacement is caused by reflections of various pulsed-laser-induced mechanical waves. We have superseded the long-established time-of-flight approach with the improved, triple-echo method. To accurately locate the origin of the laser-induced ultrasound on the plate with a known thickness, we only need to detect the arrivals of the first three consecutive mode unconverted waves. Our method works without knowing the propagation velocities of various ultrasonic waves and additionally solves some time-related drawbacks of the conventional time-of-flight approach. The relative uncertainty of the measured source-receiver separations obtained with the presented method is less than 0.01.

Marking plain surfaces using laser ablation is widely used in a serial production. However, during a laser marking of small laminated surfaces, a problem arises as a consequence of the gaps between the laminations; this tends to decrease the efficiency of the process. Therefore, a real-time measuring method that can be implemented in an industrial system for laser processing is required. In this contribution, we describe an optodynamic method for the on-line characterization of pulsed-laser marking of a laminated surface. The processing-laser beam generates an optodynamic response, i.e., the shock waves, which then spread into the surrounding gas. By using a laser-beam-deflection probe, the analysis of the obtained signals indirectly enables the real-time monitoring of the surface structure. Evaluation of the results obtained by our on-line measuring method is made by two techniques: non-destructive microscopy with extended depth of field and destructive cross-section measurements with optical microscopy. The performed experiments demonstrate that the established experimental system can simultaneously detect the changes in the laser-marking process. Furthermore, it can provide the position and the size of a gap as well as the orientation and the inclination of the samples.

Strength of the laser–tissue interaction varies even within a single tattoo because of the inhomogeneous distribution of the tattoo pigment embedded in the skin. A monitoring system is therefore developed for simultaneous monitoring of the laser tattoo removal process based on acoustical and optical techniques. A laser-beam-deflection probe is used for measuring the acoustical signals accompanying the breakdown, and a CCD camera captures the level and the spatial distribution of the plasma radiation. Using these methods we examine the degree of excitation-pulse absorption within the pigment and the degree of the structural changes of the skin. A Nd:YAG laser with a top-hat beam profile, designed for tattoo removal, is used as the excitation source in our experiments. Special attention is given to structural changes in the skin, which depend on the applied fluence. Tattoo removal with multiple pulses is also analyzed. Experiments are made in vitro (skin phantoms) and ex vivo (marking tattoos on the pig skin). The presented results are important for the understanding and optimization of the process used in medical therapies.

We present two-dimensional measurements of the laser-induced plasma development and shock wave evolution in air. The breakdown is induced by a Q-switched Nd:YAG laser (λ=1064 nm) with a pulse duration of 4 ns. To study these fast laser-induced phenomena, we have developed a high-speed, two frame shadowgraph method. It enables 2D visualization of a laser-induced event in two time instances, which are delayed by an arbitrary time interval in the range from 300 ps to 30 ns. The established method is based on 30 ps, green (λ=532 nm), and linearly polarized laser pulse, which is split into two orthogonally polarized illumination pulses for direct and delayed illumination of the breakdown area. Exploiting polarization of the probe pulses, we capture two temporally and spatially separated frames with two CCD cameras. Special attention is given to the subsequent data processing, especially to the minimization of the systematic error due to alignment of both images, and to the determination of 2D velocity distribution from the captured image pairs.

In this paper the results of research about the influences of the incident angle, the measurement distance and object colour and reflectivity on the number of acquired points while using a laser-triangulation scanner on CNC-machines, are presented. The number of points is an essential parameter of a successful 3D surface reconstructio, although it is rarely considered as a subject of research. In this research we identified the scanning parameters to acquire a sufficient number of points for any surface reconstruction. The causes of the results are also identified and could be considered when creating automatic-measurement strategies for CNC-machines. Finally,, the equation for an estimation of the number of acquired points in the optimal area of measuring parameters for the case example is also introduced.

We report on a reduced-complexity laser-diode-seeded master-oscillator-power-amplifier setup of a continuous wave fiber laser, with a single-stage ytterbium doped photonic crystal fiber amplifier. The laser is capable of generating up to 7.5 W single-transverse-mode, narrow-linewidth, polarized output suitable for second harmonic generation. The approach used possesses a further power scaling potential.

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.

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.

We present a novel method for rapid and flexible laser marking and engraving of tilted, curved and freeform work-piece surfaces. The method is based on integrating a three-dimensional (3D) laser measurement system into a 3D laser marking system. We use the same laser source and optics for measurement and processing with a minimum of additional hardware components. A low power CW laser regime is used to measure the 3D shape of a work-piece surface while a high-peak power-pulsed laser regime is used for processing. The acquired 3D surface data are used to determine the 3D trajectory of the processing beam focus. Neither the 3D shape of the work-piece nor its orientation needs to be known in advance as long as the processed surface lies within the working range of the 3D laser processing system. This eliminates the need for exact work-piece positioning before processing and substantially improves processing flexibility (allowing, e.g. variations in work-piece shape or/and orientation from mark to mark). This paper discusses key issues concerning an implementation of the method and presents typical examples of markings and engravings, which demonstrate the advantages of the method with respect to the existing industrial 2D and 3D laser marking and engraving methods. The method can also be applied to flexible laser structuring and microprocessing of curved surfaces.

Introducing specific textures on a tribological surface can contribute to friction reduction in sliding contacts. Well defined micro-dimples can act as lubricant reservoirs capable of feeding lubricant directly into the contact and initiating micro elasto-hydrodynamic lubrication, as well as traps for wear debris. A lot of experimental work has been already carried out, but it is mostly based on trial and error approach when defining optimum textures for a given application.

This article examines the influence of incident angle, object colour and measurement distance on the computer numerically controlled laser scanning process. To determine the physical background of these influences, the operation of the triangulation sensor, the surface reflection and the colour properties of the measured object were analysed. The various influences and their physical background are explained by using a test-measurement setup, which makes it possible to investigate a specific influencing factor. The article concludes with several guidelines that should be followed in order to obtain better measurement results.

We present a method that enables an automated assessment of the geometrical dimensions of power transmission belts and the detection of surface defects and small deviations from the ideal shape that are difficult to detect with a visual inspection. The method is based on the acquisition of belt surface profiles using a laser triangulation and automated profile assessment based on a custom-developed algorithm. The algorithm uses a novel approach to profile segmentation, featuring a template that defines the expected profile shape in advance and so, allows a faster implementation of the algorithm. It enables an automated calculation of the basic geometrical dimensions, which define the profile shape in the technical drawing and are important for online quality control in the production line. A macrolanguage was developed for a rapid and flexible definition of the mathematical operations used in the calculation of the profile's dimensions and thus, an adaptation to the requirements of a particular application. We demonstrate the use of the automatic belt profile geometry assessment on randomly chosen samples.

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.

An indirect laser-induced method for selective removal of large copper areas from a printed circuit board is theoretically and experimentally investigated. The results show that the threshold condition for the process involves phase transition of the epoxy-based substrate resin. Optimal parameters for maximizing process speed are found and discussed.

We present an optodynamic measurement of a laser-induced cavitation bubble and its oscillations based on a scanning technique using a laser beam-deflection probe. The deflection of the beam was detected with a fast quadrant photodiode which was built into the optical probe. The applied experimental setup enabled us to carry out one- or two-dimensional scanning of the cavitation bubble, automatic control of the experiment, data acquisition and data processing. Shadow photography was used as a comparative method during the experiments.

We present a new method for monitoring of the laser micro-drilling process. The method is based on detection of acoustic waves in air above the processed sample using a laser beam deflection probe (LBDP). We present an augmentation of the experimental set-up by means of a digital micrographic system which enables the acquisition of images of the plasma plume and of the hole cross-section during a drilling sequence. Comparing the acquired images with the detected LBDP signals, we examine the drilling process from a new perspective.

Recently, we developed an optodynamic experimental technique that makes it possible to measure the linear momentum obtained by a metal target sample in the shape of a rod during a nanosecond laser pulse interaction in the ablative regime. The height of the rod’s rear end axial step-like displacement, caused by the first reflection of the laser-generated ultrasonic wave, is proportional to the linear momentum acquired by the rod. In comparison with commonly used ballistic methods, we can determine the acquired momentum on a much shorter time scale corresponding to the wave transition time, from the front to the rear end of the rod. Using this method we investigated the ambient air pressure dependence on the formation of linear momentum over a laser intensity range, from the ablation threshold to values about ten times higher. Steel rods of various diameters were used to demonstrate the effect of an expanding blast wave which delivers additional momentum to the target, when the laser beam on the target surface is smaller than the target itself. The typical value of the acquired target momentum is on the order of μN s and 10 μN s/J for the momentum coupling coefficient.

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.

Shadow photography and laser-induced breakdown spectroscopy (LIBS) are studied as methods for monitoring the selective removal of thin (i.e., under 100 [micro]m) layers by laser ablation. We used a laser pulse of 5 ns and 16 mJ at 1064 nm to ablate an 18-[micro]m-thin copper layer from the fiberglass substrate. On the basis of shadowgraphs of the laser-induced shock waves, we measured the optodynamic energy-conversion efficiency, defined as the ratio between the mechanical energy of the shock wave and the excitation-pulse energy. Our results show that this efficiency is significantly higher for the laser pulse-copper interaction than for the interaction between the excitation pulse and the substrate. LIBS was simultaneously employed in our experimental setup. The optical emission from the plasma plume was collected by using a spectrograph and recorded with a streak camera. We show that advancing of laser ablation through the copper layer and reaching of the substrate can be estimated by tracking the spectral region between 370 and 500 nm. Therefore, the presented results confirm that LIBS method enables an on-line monitoring needed for selective removal of thin layers by laser.

A Nd:YAG laser photodisruption is a well-established tool for intraocular surgery, such as treatment of posterior capsule opacification that affects the visual function. During the intraocular procedure, called laser capsulotomy, the excitation pulse is focused several times just behind the posterior capsule and intraocular lens to create the central opening in the opacified capsule. We built an in vitro experiment to (1) clarify the influence of the distance between the intraocular lens and the posterior capsule on the total pulse energy required for the capsulotomy, and (2) investigate the main mechanisms responsible for the posterior capsule opening. In our in vitro model, different distances between the solid boundary (imitating an intraocular lens) and the membrane (imitating the posterior capsule) simulate different types of posterior capsule opacification. Our results show that procedure efficiency decreases by decreasing distance between the lens and the capsule. We also explain that for smaller distances between the pulse focus and the membrane, plasma and shock wave are responsible for the capsule disruption. Here, a risk of collateral damage significantly increases. On contrary, the membrane and the bubble jet disrupt the membrane, when pulse focus is moved away and the risk of intraocular lens damage decreases. However, the membrane disruption is not very effective, if it is placed near the solid boundary that inhibits the membrane jet.

A lack of reproducible and practical methods to assess venous leg ulcer healing is a major problem encountered by investigators evaluating various treatments. We aimed to compare a new laser-based three-dimensional (3D) measuring device with computer planimetry with photography for the assessment of venous leg ulcers, and to estimate the reliability of measurements by the methods. Sixty measurements of perimeter and area of 15 venous leg ulcers, < 10 cm in diameter (eight patients; six females; mean age 71 years; range 52-90 years), were made with both methods. Two independent investigators performed the measurements at the first visit and 2-4 weeks later. The precision and accuracy of the methods were determined and compared. The accuracies for computer planimetry with photography in comparison with the laser-based 3D measuring method were 8.4% for perimeter and 16.0% for area measurements. The precisions of ulcer area and perimeter measurements did not differ significantly between the two methods (p=0.993 and 0.201, respectively). The main advantage of the laser-based measuring method is the 3D ulcer measurement with a precision of 7.5%, which also takes into account distortions created by the limb convexity. The system is accurate, inexpensive, user-friendly, and appropriate for everyday practice.

Conversion of light to thermal and mechanical energy in the vicinity of the water–air interface was studied experimentally. The focus of an IR pulsed laser was moved in steps in vertical direction from the position inside the water upwards to the position slightly above the surface, in the air. The generated optodynamic waves were detected by probe beam deflection. Two probe beams were used simultaneously, both laying parallel to the surface, one inside the water and the other one in the air. The analysis and comparison of the waveforms captured in the two media provide information about the position and size of the optodynamic source relative to the interface, indicating the relative efficiency of thermal energy conversion that takes place in the vicinity of the interface both in the air and inside the water. Three positions of the optodynamic source can be determined from the waveforms: in the air, at the interface and inside the water.

Laser induced breakdown in water represents an abrupt high intensity photoacoustic phenomenon. The pressure front that appears at its site represents an ultrasonic shock wave spreading into surrounding water. At the same time the cavitation bubble develops. The effect of both is particularly important in ocular microsurgery, where Q-switched lasers are used to vaporize the tissue in procedures such as posterior capsulotomy. Formation of the cavitation bubble and the propagation of the sound wave were analyzed by an optodynamic experimental set-up. It is based on two-dimensional scanning technique using a beam deflection probe. From the beam deflection probe signals the time of flights for both the sound wave and the cavitation bubble were determined. By using Hugoniot curves and the two-dimensional time of flight data field the pressure amplitude in the front was estimated. Simultaneously the expansion of the cavitation bubble was also analyzed and its energy was determined.

Background The main purpose of this research was to develop a new method for differentiating between scoliotic and healthy subjects by analysing the curvatures of their spines in the cranio-caudal view. Methods The study included 247 subjects with physiological curvatures of the spine and 28 subjects with clinically confirmed scoliosis. The curvature of the spine was determined by a computer analysis of the surface of the back, measured with a non-invasive, 3D, laser-triangulation system. The determined spinal curve was represented in the transversal plane, which is perpendicular to the line segment that was defined by the initial point and the end point of the spinal curve. This was achieved using a rotation matrix. The distances between the extreme points in the antero-posterior (AP) and left-right (LR) views were calculated in relation to the length of the spine as well as the quotient of these two values LR/AP. All the measured parameters were compared between the scoliotic and control groups using the Student’s t-Test in case of normal data and Kruskal-Wallis test in case of non-normal data. Besides, a comprehensive diagram representing the distances between the extreme points in the AP and LR views was introduced, which clearly demonstrated the direction and the size of the thoracic and lumbar spinal curvatures for each individual subject. Results While the distances between the extreme points of the spine in the AP view were found to differ only slightly between the groups (p = 0.1), the distances between the LR extreme points were found to be significantly greater in the scoliosis group, compared to the control group (p

Optodynamics treats optical manipulation as a superposition of time-developing wave motion induced by a light-matter interaction. When an opaque solid object is manipulated by a pulse of light, various types of mechanical waves are launched from the illuminated surface: ablation-induced waves (AIWs) resulting from material recoil, thermoelastic waves (TEWs), and the light-pressure-induced waves (LIWs) emanating exclusively due to radiation pressure. The manipulated object’s boundaries experience staircase-like displacements with discrete steps caused either by AIWs or LIWs each time these waves are reflected from the interfaces. On the contrary, TEWs cannot translate the center of mass of the manipulated object, but their presence can be inferred from the transient, bi-polar displacements around the equilibrium position.

We treat the light-matter interaction due to radiation pressure in one dimension using the fundamental, nonrelativistic conservation principles of energy and momentum. Additionally, we assume that the center of mass-energy maintains the same uniform motion if the interaction takes place or not. Since we handle solids as elastic objects, the results are consistent with the principle of causality and agree with recent experimental observations. We analyze the problem of reflection of a light pulse from a fully-reflective mirror and show that its reflection gives rise to an elastic wave with a measurable amplitude and a correct Doppler shift of the reflected pulse. We also analyze the problem of light pulse transmission into an anti-reflection coated, non-dispersive and lossless dielectric, where an elastic wave may as well be accompanied by a mechanical wave escorting the light pulse. We show that the Balazs rigid box thought experiment can be also realized in elastic dielectrics where some of the energy of the incident light is transferred to the wave motion. It follows from our approach that the electromagnetic momentum of the light pulse in the dielectric acquires Abraham’s form only when a single type of the mechanical waves accompanies the interaction.

During the interaction of a laser pulse with the surface of a solid object, the object always gains momentum. The delivered force impulse is manifested as propulsion. Initially, the motion of the object is composed of elastic waves that carry and redistribute the acquired momentum as they propagate and reflect within the solid. Even though only ablation- and light-pressure-induced mechanical waves are involved in propulsion, they are always accompanied by the ubiquitous thermoelastic waves. This paper describes 1D elastodynamics of pulsed optical manipulation and presents two diametrical experimental observations of elastic waves generated in the confined ablation and in the radiation pressure regime.

A practical optodynamic study was performed to determine the usability of different lengths of laser pulses for the generation of ultrasonic transients in a solid material. The aim of the study was to evaluate the possibility of a dual use for a laser pulse—for laser material processing, on the one hand, and for the ultrasonic wave generation on the other—with both processes being combined on the same production line. The propagation of the laser-generated ultrasonic waves is evaluated by detecting and measuring with a PID-controlled stabilized interferometer. Thus, both systems provided the basic tools, the generation and detection of ultrasonic waves, for an ultrasonic, laser-based, non-destructive material evaluation. The ultrasonic transients generated by ‘classical’ nanosecond laser pulses were compared with the transients generated by industrial laser pulses with a duration of a few tenths of a microsecond. The experimental results are compared with the results of a time-of-flight analysis that also involved part of a mode-conversion analysis for both regimes in a layered material structure. The differences between the two waveforms were assessed in terms of their visibility, wavelength and resolution. The limit values were calculated and estimated for the laser-pulse parameters, when such pulses are intended for use in an ultrasonic, laser-based, non-destructive evaluation. The possibility of using an industrial marking laser for laser ultrasound generation is thus demonstrated.

The present paper reports a new setup for acquisition of shape data for weldpieces during pulsed laser welding. The setup is based on illumination of the weldpiece surface by laser light, which is structured as multiple light planes, and acquisition of the image of the illuminated surface by a digital camera. The position of the optical system is fixed relative to the measured weldpiece. The acquired image is fed into a personal computer where it is processed to obtain the three-dimensional shape of the part of the weldpiece surface that was imaged by the camera. A setup that allows up to 20 shape measurements per second was developed based on this principle. The setup was applied to examine distortion of weldpieces during laser welding of low carbon thin steel sheets. According to the results the setup allows a rapid and accurate temporally and spatially resolved evaluation of weldpiece distortion.

In recent years, a large number of linear and nonlinear laser-based diagnostic techniques for detection of pollutions in different environments have been developed. Applications of laser spectroscopy constitute a vast field, which is difficult to cover comprehensively in a review. Due to that here are presented only a few spectroscopic methods, chosen to illustrate the power of applied laser spectroscopy in environmental pollution investigation. The paper also gives a brief presentation of main laser spectroscopy methods.

This paper deals with a laser-cleaning process for removing a layer of paint. The effects of each individual laser pulse were monitored by a three-probe system. Ultrasonic signals from the rear surface of the substrate were obtained using an arm compensated Michelson interferometer, the optoacoustic waves in the surrounding air were detected using a laser beam deflection probe and the shape of the growing crater was measured using a laser anamorph profilometer. Two different cleaning lasers were used: an Excimer and a Nd:YAG laser. Typical parameters of the optodynamic signals versus the laser-pulse number are presented. A linear correlation between the quantity of ablated material and the integral of the ultrasonic signals was found together with an exponential relationship between the time-of-flight of the optoacoustic signals and the decoating rate.

Generation of shock waves during a dry laser-cleaning process was examined with the probe-beam-deflection technique. Our experimental set-up allows measurement of a density gradient and a time of flight of the generated optoacoustic waves. With analysis of the measured signals we observed supersonic propagation velocities, density profiles matching the shock-wave profile, and reasonable agreement between the shock-wave theory and measured data. Furthermore, we inspected the mechanisms for the generation of these optoacoustic waves. For the clean surface a rapid thermoelastic surface expansion is the main generation mechanism, creating only weak shock waves; however, during the dry laser cleaning the ejected contaminants generate relatively strong shock waves. This difference is easily observed with our experimental set-up, thus enabling the on-line monitoring of the laser-cleaning process.

Background The main objective of the present method was to automatically obtain a spatial curve of the thoracic and lumbar spine based on a 3D shape measurement of a human torso with developed scoliosis. Manual determination of the spine curve, which was based on palpation of the thoracic and lumbar spinous processes, was found to be an appropriate way to validate the method. Therefore a new, noninvasive, optical 3D method for human torso evaluation in medical practice is introduced. Methods Twenty-four patients with confirmed clinical diagnosis of scoliosis were scanned using a specially developed 3D laser profilometer. The measuring principle of the system is based on laser triangulation with one-laser-plane illumination. The measurement took approximately 10 seconds at 700 mm of the longitudinal translation along the back. The single point measurement accuracy was 0.1 mm. Computer analysis of the measured surface returned two 3D curves. The first curve was determined by manual marking (manual curve), and the second was determined by detecting surface curvature extremes (automatic curve). The manual and automatic curve comparison was given as the root mean square deviation (RMSD) for each patient. The intra-operator study involved assessing 20 successive measurements of the same person, and the inter-operator study involved assessing measurements from 8 operators. Results The results obtained for the 24 patients showed that the typical RMSD between the manual and automatic curve was 5.0 mm in the frontal plane and 1.0 mm in the sagittal plane, which is a good result compared with palpatory accuracy (9.8 mm). The intra-operator repeatability of the presented method in the frontal and sagittal planes was 0.45 mm and 0.06 mm, respectively. The inter-operator repeatability assessment shows that that the presented method is invariant to the operator of the computer program with the presented method. Conclusions The main novelty of the presented paper is the development of a new, non-contact method that provides a quick, precise and non-invasive way to determine the spatial spine curve for patients with developed scoliosis and the validation of the presented method using the palpation of the spinous processes, where no harmful ionizing radiation is present.

A new method for rapid and accurate acquisition of the shape of an electrode indentation in a workpiece during resistance spot welding (RSW) is presented. The method is based on illumination of the indentation with structured laser light and detection of the image of the illuminated object using a charge coupled device camera. The image from the camera is digitised using a frame grabber and fed into a personal computer where it is processed and analysed. This paper presents the basic principles of the method and discusses the image processing algorithms developed to measure the indentation shape characteristics, such as diameter, depth, and volume. Results from an application of the method to study electrode wear during RSW of zinc coated steel are also presented.

Laser cleaning is an optodynamic process in which the optically induced removal of a liquid or a solid contaminant from a substrate is accompanied by a optoacoustic wave in the surrounding air. In our experiments we used both dry and steam laser-cleaning techniques for various samples. Optoacoustic wave, produced by the abrupt heating and detachment of the contaminants, was observed with a probe-beam deflection technique. We determined two characteristic parameters of the optoacoustic wave: the amplitude and the time-of-flight of the acoustic signal. With an analysis of these waves we also determined possible generating mechanisms. The decrease of the amplitude and the velocity of propagation, which approaches sonic speed, of the consecutive waves indicate that the dynamics during the laser-cleaning process is progressively weakened. The cleaning process is over when both the parameters reach a constant value, so with measuring optoacoustic waves the progress of the cleaning process could be observed on-line.

An analytical model is presented that describes the bending process following the absorption of a Gaussian laser pulse by the surface of a moderately thick metal plate. The model is based on the constitutive equations of thermoelastoplasticity and therefore fundamentally describes this optodynamic process. Assuming relatively short laser pulses, Green's function is used as an approximation for the real plate temperature. The plate is assumed to be made of elastic, linearly hardening material.