When an erbium-laser pulse is directed into water through a small-diameter fiber tip (FT), the absorption of the laser energy superheats the water and its boiling induces a vapor bubble. We present ...the influence of different FT geometries and pulse parameters on the vapor-bubble dynamics. In our investigation, we use a free-running erbium: yttrium aluminum garnet (Er:YAG) (
) laser that was designed for laser dentistry. Its pulse is directed into the water through FTs with a flat and conical geometry. Our results show that in the case of the conical FT, a spherical bubble is induced, while a channel-like bubble develops for the flat FT. The ratio between the mechanical energy of the liquid medium and the pulse energy, which we call the optodynamic energy-conversion efficiency, is examined using shadow photography. The results indicate that this efficiency is significantly larger when a conical FT is used and it increases with increasing pulse energy and decreasing pulse duration. The spherical bubbles are compared with the Rayleigh model in order to present the influence of the pulse duration on the dynamics of the bubble's expansion.
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.
•Modeling using Green’s function formalism and streamlined Huygens’ principle.•The model incorporates spatial distributions of source and sensor sensitivity.•A statistically simplified area-to-area ...ultrasound transfer function was developed.•Uniform, Gaussian and annular source ultrasonic waveforms are simulated.•Thus-simulated waveforms match the measurements more closely than the point model.
The near-field, surface-displacement waveforms in plates are modeled using interwoven concepts of Green’s function formalism and streamlined Huygens’ principle. Green’s 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.
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 Green’s 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.
We use an optodynamic model to study the interaction of pulsed laser radiation of different duration with mono- and polydisperse dimers and trimers of plasmonic nanoparticles as resonant domains of ...colloid Ag multiparticle aggregates. A comparative analysis of the influence of pulse duration on the kinetic characteristics of domains accompanied by the change in their local structure was carried out taking into account the intensity of incident radiation. The obtained results explain the reasons for laser photochromic reactions in materials containing colloidal aggregates of plasmonic nanoparticles.
This paper describes an analysis of pulsed lasers micro-drilling of different metals. Study focuses to an optodynamic phenomenon which appears as thermal effects induced by laser light pulses and ...leads to dynamic process manifested as ultrasonic shock waves propagating into the sample material. The shock waves are detected by a non-contact optical method by using arm compensated Michelson. Monitoring of the main parameters of the micro drilling such as material ablation rate and efficiency was realized by analysis of the optodynamic signals. The process is characterized by decreasing ablation rate that leads to the finite hole depth. The experimental part of study comprehends a comparison between various metals. In order to describe decreasing ablation rate a theoretical model based on the energy balance is proposed. It considers the energy/heat transfer from the laser beam to the material and predicts a decreasing drilling rate with an increasing number of successive laser pulses. According to the proposed model, the finite depth of the hole appears as a consequence of the increasing surface area through which the energy of the laser beam is conducted away to the material around the processed area. Decreasing ablation rate and the finite hole depth predicted by model were in good agreement with the experimental results.
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.
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