Influence of water environment on holmium laser ablation performance for hard tissues

This study clarifies the ablation differences in air and in water for hard biological tissues, which are irradiated by fiber-guided long-pulsed holmium lasers. High-speed photography is used to record the dynamic characteristics of ablation plumes and vaporization bubbles induced by pulsed holmium lasers. The ablation morphologies and depth of hard tissues are quantitatively measured by optical coherence microscopy. Explosive vaporization effects in water play a positive role in the contact ablation process and are directly responsible for significant ablation enhancement. Furthermore, water layer depth can also contribute to ablation performance. Under the same laser parameters for fiber-tissue contact ablation in air and water, ablation performances are comparable for a single-laser pulse, but for more laser pulses the ablation performances in water are better than those in air. Comprehensive knowledge of ablation differences under various environments is important, especially in medical procedures that are performed in a liquid environment.     

Interaction of holmium laser radiation and cortical bone: ablation and thermal damage in a turbid medium

The ablation of cortical bone by holmium laser radiation is described by experimental values of the ablation rate, the depth of tissue damage, and the tissue temperature. An ablation model is presented on the basis of photon diffusion in a turbid medium. When this model is compared with experimental results for the ablation rate, the penetration depth is determined. The expansion of the laser-induced heat can be explained by a point heat source located in a distance beneath the surface equal to the ablation depth. The accumulation of heat as a function of the repetition rate of the laser leads to a limitation of the repetition rate. In order to avoid traumatic heat accumulation, a maximum repetition rate should not be exceeded.     

Femtosecond pulsed laser ablation and deposition of titanium carbide

In this work we have evaporated a titanium carbide target by an Nd:glass laser with 250 fs pulse duration. The plasma produced from the ablation has been characterized by Intensified Coupled Charge Device (ICCD) fast imaging, optical emission spectroscopy and quadrupole mass spectrometry, while X-ray Diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDX), X-ray Photoelectron Spectroscopy (XPS) and Scanning and Transmission Electron Microscopy have been used to study the deposited film morphology and composition. The plume shape and front velocity are very similar to those found in other systems and are typical of femtosecond ablation. In particular the front velocity is 1.1 × 10⁷ cm s^− 1 at a laser fluence of 1.9 J cm^− 2, while the value of the cosine exponent is 4.5 in the same conditions. In the TiC system a delayed emission, found by ICCD imaging and emission spectroscopy, is also present. In fact, although the emission involved in the “traditional” plume ends after about 1 μs, the target is still hot and gives origin to another emission, expanding with a velocity that is about two orders of magnitude lower compared to that of the traditional plume (2.2 × 10⁴ cm s^− 1 at a laser fluence of 1.9 J cm^− 2).The results of the analysis of both the gaseous plume and the deposited films seem to indicate that in the case of TiC system the presence of a large number of particles ejected from the target is responsible for the formation of the films. XPS and EDX data indicate that the stoichiometry of the target is preserved in the films, while XRD analysis shows that the films are amorphous in structure.     

Laser-fiber system for ablation of intraocular tissue using the fourth harmonic of a pulsed Nd:YAG laser

We report on a method for delivering high fluence pulsed 266 nm laser radiation to the target tissue via an optical fiber. The fourth harmonic of a Nd:YAG laser was concentrated using a hollow glass taper and launched into an optical fiber. Fluences of up to 2 J/cm(2) were routinely output at the tapered optical fiber tip. The maximum fluence generated before failure of the optical fiber was between 3.5 and 8 J/cm(2). Ablation of ocular tissue was demonstrated using fluences of 1.0 and 0.4 J/cm(2). The delivery system has the potential for use in intraocular surgical procedures.     

Determination of the optical-breakdown threshold under irradiation of condensed inclusions by pulsed laser radiation

On the basis of the thermal approach, a mathematical model of the optical breakdown on condensed inclusions exposed to pulsed laser radiation is developed. As individual stages of the process, we consider the particle heating and evaporation, the formation of a vapor aureole and its ionization, as well as the propagation of shock waves in the space surrounding the particle. The threshold characteristics of the laser-beam parameters sufficient for initiating an optical breakdown on metal and dielectric particles, as well as on dielectric liquid drops are determined. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 6, pp. 106–117, November–December, 2005.     

Effect of aging on copper nanoparticles synthesized by pulsed laser ablation in water: structural and optical characterizations

Effect of aging on copper nanoparticles synthesized by pulsed laser ablation of copper plate in water was studied. By characterization studies of the aged nanoparticles, it is found that copper nanoparticles converted into Cu@Cu₂O nanostructure. The synthesized nanomaterial is characterized with UV-Visible absorption, transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman and photoluminescence (PL) spectroscopic techniques. TEM image shows that the aged nanoparticles get assembled into cactus like structure and are spherical in shape with average diameter 7 nm and dispersion 2 nm. XRD and FTIR spectrum confirm the formation of Cu@Cu₂O in the aged sample. Raman spectrum also confirms the presence of Cu₂O nanoparticles. PL spectrum of the aged nanoparticles shows a direct allowed transition with bandgap energy of 2·24 eV. The mechanism for synthesis of core-shell nanoparticles and formation of self-assembly of nanoparticles is also discussed.     

Film formation during pulsed laser ablation of nickel-palladium composite targets

The films of Pd, Ni, and a Ni-Pd alloy have been obtained by pulsed laser ablation of Ni-Pd composite targets and characterized by electron diffraction, transmission electron microscopy, and vibrating-sample magnetometry techniques. It is established that a nonmagnetic metastable hexagonal phase is formed in Ni and Ni-Pd films. Upon annealing, these films acquire an equilibrium cubic structure and exhibit hysteresis during the magnetization reversal. The dependence of the solid-solution lattice constant on the concentration exhibits a positive deviation from Vegard’s law, which is characteristic of alloys with concave liquidus curves.     

Carbon nitride films deposited by reactive sputtering and pulsed laser ablation

Carbon nitride films were deposited by reactive sputtering process and by pulsed laser ablation process with substrate bias. By applying the RF bias, it enables the ion irradiation on to the depositing film surface continuously. ECR plasma source was used for reactive sputtering. Nd:YAG laser (λ=532 nm, 210 mJ) was used to ablate a graphite target in the nitrogen atmosphere. The film properties were examined by XPS, Raman, nanoindentation measurement, and FE-SEM. It was shown that the films deposited by reactive sputtering had smooth surface and its hardness of approximately 30 GPa. However, the films deposited by pulsed laser ablation had uneven surface and low hardness. Both processes, the atomic composition ratio of N/C and sp³ bonding ratio increased with ion bombardment energy up to 100-150 eV, and level off above it. The maximum atomic composition ratio of N/C was 0.35 for reactive sputtering and 0.24 for laser ablation.     

Conversion-characteristic nonlinearity for periodic pulsed laser radiation acting on microwire bolometers

Expressions are derived for the normalized conversion coefficients for a thin- wire bolometer acted on by high-intensity periodic laser pulses, which relate the resistance change and the area under the cooling curve to the energy incident per unit length, the pulse repetition frequency, and the nonuniformity in the energy distribution along the bolometer. Results are given for a platinum bolometer and a wavelength of 10.6 m. A method is given for eliminating the systematic error due to the conversion nonlinearity.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 30–32, September, 1993.     

Nanocrystalline silicon films formed under the impact of pulsed excimer laser radiation on polyimide substrates

Polycrystalline silicon films on polyimide substrates were obtained by a method based on the crystallization of amorphous films under the impact of nanosecond pulses of excimer laser radiation. Characteristics of the film structure were studied by methods of Raman scattering and high-resolution electron microscopy. For the laser crystallization regimes employed, nanocrystalline silicon films with an average grain size of 5 nm were obtained. The results are of interest for the development of large-scale microelectronic devices (active thin-film transistor matrices) on cheap flexible substrates.     

Simulation of the process of sintering of spherical powders under the effect of pulsed laser radiation

Numerical simulation is performed of the process of sintering of a charge of two layers of spherical particles under the effect of pulsed and pulse-periodic laser radiation of wavelength λ = 1.06 μm and duration of 1–5 ms. __________ Translated from Teplofizika Vysokikh Temperatur, Vol. 44, No. 1, 2006, pp. 148–152. Original Russian Text Copyright ? 2006 by M. V. Petrushina, E. L. Pogudo, and Yu. A. Chivel’.     

Monte Carlo simulation of pulsed laser ablation into an ambient gas

Laser ablation from one- and two-component targets into a diluted gas background is simulated by combined direct simulation-test particle Monte Carlo method. The spatial and velocity distributions of particles deposited at the plane substrate are calculated. The approach developed has allowed us to consider the influence of the collisions both among the ablated particles and between the ablated and ambient gas particles on the uniformity of film stoichiometry. It is found that the increase of the background gas pressure results in the more uniform distribution of the stoichiometrical ratio of the deposited particles with different masses.     

Nanoparticles of antimony sulfide by pulsed laser ablation in liquid media

In the present article, antimony sulfide nanoparticles have been synthesized by pulsed laser ablation of an antimony sulfide pellet in distilled water and isopropyl alcohol. The target was irradiated by 1064 and 532 nm from a pulsed Nd:YAG laser operated at 10 Hz and pulse width of 10 ns at room temperature. Analysis of the morphology, crystalline phase and elemental composition were done using transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The optical band gap energies of these colloidal nanoparticles were evaluated from UV–Visible absorption spectra. It was observed that the morphology, size, and optical properties of the antimony sulfide nanoparticles depend on the wavelength of the laser and the liquid media.