Optical Breakdown Research Articles

Modification of the Cu-Zr bronze surface by exposure to powerful UV laser pulses

The laser pre-treatment of Cu-Zr alloy surface for diffusion welding, which is used in the aerospace industry for joining dissimilar materials, has been investigated. The effect of a nanosecond UV laser pulse on the surface of Cu-Zr alloy samples was studied. It was found that at a pulse energy density E ∼ 0.2-1 J/cm2 pre-ablative microscopic effects of mainly thermal nature were observed in the metal, also there were uplifts of material in the irradiated zone. The surface profile of the sample in the irradiated zone corresponds to the energy distribution of the laser beam. Significant deformations occurred in the crystal structure of the surface layer, and an irreversible configuration of the metal surface was created. At E ≥ 1 J/cm2 an optical breakdown with the formation of a plasma torch and with the appearance of a classical laser crater was observed. The arising erosion of the surface prevented registration of this effect. Microanalysis showed that the concentration of zirconium in the surface layer of the metal after exposure decreased.

Heat Treatment of the Surface of the ChS57 Alloy with Powerful Nanosecond Ultraviolet Laser Pulses

The threshold of optical breakdown of the nickel alloy ChS57 (Inconel) was measured at a wavelength of 0.355 μm with a laser pulse duration of 10 ns. Heat treatment of ChS57 above pulse energy density threshold (1 - 2.5 J/cm2) occurred mainly in the ablative mode with almost no melting. The elemental composition of the surface layer did not change at an irradiation in a fixed spot. When a laser beam moves along the surface of the sample at a speed of 1 mm / s and at pulse energy density of about 0.02 J/cm2, oxygen was detected in the elemental composition (3 – 4 wt. %). However, the proportions of the elemental composition of the alloy remained virtually unchanged. Heat treatment under threshold at pulse energy density ≥ 0.25 J/cm2 revealed a rise of the surface layer with traces of high-temperature plastic deformation in the form of slippage on grain boundaries and crystallographic slip.

Features of optical breakdown of aqueous colloidal solutions of ferric oxide (Fe2O3) nanoparticles occurring on individual or on two closely located nanoparticles

• Optical breakdown in a solution of nanoparticles occurs according to 2 scenarios. • In 78%, breakdown occurs on one nanoparticle (NP), in 22% – on two NPs. • In the case of two NPs, cavitation bubbles with plasma move away from each other at a speed of 3000 m/s. • The motion of flash occurs under the influence of a shock wave from an neighboring breakdown. • Estimated pressure at the shock wave front is 2300 MPa. A streak camera was used to study the dynamics of the development of plasma flashes of the optical breakdown that occurs in aqueous solutions of Fe2O3 nanoparticles. It is shown that optical breakdown can occur according to two scenarios – initiated on single nanoparticle (78%) or on two closely located nanoparticles (22%). When optical breakdown occurs on two nanoparticles, cavitation bubbles move away from each other on 50 μm with velocity of 3000 m/s under the action of shock waves initiated by the optical breakdown on neighboring particles. The estimated pressure at the shock wave front is approximately 2300 MPa.

Comparison of initial pressure distributions in shock wave simulation of optical breakdown on surface

In this work we investigated the velocity of propagation of a shock wave after optical breakdown on the surface, depending on various initial pressure distributions which are simulated in Ansys Fluent. When setting of the shock wave energy of the order of 10 … 20% of the laser pulse energy, results are in satisfactory agreement with experiments. An analysis of the experimental data showed an effect when the velocities of shock waves propagation are comparable but energies of laser pulses differ by two orders of magnitude between each other, which leads to significant deviations from the theory of a point explosion.

Propagation of Shock Wave at the Cavitation Bubble Expansion Stage Induced by a Nanosecond Laser Pulse

Abstract The objective of this paper is to reveal the attenuation characteristics of a shock wave after optical breakdown in water, with laser pulses of 12-ns duration. A high time-resolved shadowgraph method is applied to capture the temporal evolutions of the cavitation bubble wall and shock wave. The experiments are carried out on a single bubble generated far away from the free surface and the rigid walls with laser pulse energies of 22 mJ, 45 mJ, and 60 mJ. The results show that a high, time-resolved, wave front velocity of the shock wave is identified, and the maximum velocity can reach up to around 4000 m/s. An asymmetric shock wave is observed at the very start of the bubble expansion stage, and the process of the sharp attenuation of wave front velocity down to sound velocity is accomplished within 310 ns. The possible relationship of the cavitation bubble and the shock wave is discussed and a prediction model, using the maximum bubble radius and the corresponding time calculated by the Gilmore model, is proposed to calculate the location of the wave front.

Laser plasma etching of electronic materials on the example of diamond and sapphire

The work addresses the issues of laser plasma etching of electronic materials on the example of the separation of diamond and sapphire plates into crystals. The developed method is based on a physical phenomenon – an optical breakdown in specially selected gas environments in which plasma is set on fire and plasma etching of sub-base materials (plates) with the for-mation of volatile products of chemical reactions and their evacuation by vacuum system. The work was carried out in the range of working pressures of 110-3–110-1 Torr. Fluoride sys-tems were used as work environments: (SF6/O2; CClF3/O2; F2, etc.) and pure oxygen (O2). Both the system – fluoride and oxygen "work" well. The oxygen system is preferable for eco-nomic and environmental reasons.

Synergistic effect of picosecond optical and nanosecond electrical pulses on dielectric breakdown in aqueous solutions

The combined effect of short (picosecond) optical and (nanosecond) electrical pulses on dielectric breakdown is investigated both theoretically and experimentally. It was demonstrated that nanosecond electrical pulses (nsEPs), being applied simultaneously with picosecond optical pulses, reduce the threshold for optical breakdown. Experimental results are discussed with respect to an extended model for opto-electrical-induced breakdown. The newly unveiled effect is expected to play a significant role in spatially confined electroporation and further advances in laser-ablation-based processes while also allowing for measurements of ambipolar diffusion constants.

Case Report: Investigation of the Time Evolution of Optical Breakdown Plasma During Irradiation of Aqueous Solutions of Fe Nanoparticles

The time sweeps of images of optical breakdown plasma flashes under irradiation of aqueous solutions of Fe nanoparticles with Nd: YAG laser radiation (λ = 1,064 nm, τ = 10 ns, ν = 10 kHz, ε = 2 mJ) are studied. It is shown that the sizes of plasma flares, the plasma glow intensity, and the time to reach the maximum intensity are concentrated around certain values. So, for example, the values of 30 μm are most typical for the maximum size of flares. The maximum luminescence is usually reached in 3–4 ns. It is found that at initial stage of optical breakdown process the water-vapor boundary moves at typical speed of 11 km/s and have maximum and minimum values at 15 and 4 km/s respectively. It is assumed in this work that such a distribution may be associated with the initiation of breakdown on nanoparticles located in different places of the laser radiation waist.

Femtosecond-Laser Assisted Surgery of the Eye: Overview and Impact of the Low-Energy Concept.

This article provides an overview of both established and innovative applications of femtosecond (fs)-laser-assisted surgical techniques in ophthalmology. Fs-laser technology is unique because it allows cutting tissue at very high precision inside the eye. Fs lasers are mainly used for surgery of the human cornea and lens. New areas of application in ophthalmology are on the horizon. The latest improvement is the high pulse frequency, low-energy concept; by enlarging the numerical aperture of the focusing optics, the pulse energy threshold for optical breakdown decreases, and cutting with practically no side effects is enabled.

Visualization of volumetric defects and dynamic processes in crystals by digital IR-holography.

The observation and study of defects of single-crystal multicomponent optical material is necessary to determine the qualitative characteristics and optical properties of a material and to diagnose its manufacturing procedures. This paper utilizes the digital IR-holography to measure the geometrical parameters, shape, and location of defects as well as to characterize them. The paper illustrates the examples of physical, chemical, and optical inhomogeneities. Also, the paper presents the results of the study of dynamic processes in optical elements under the influence of laser radiation with high power density. The possibility of using the digital holographic technology to determine the dynamics of optical breakdown in the ZnGeP2 single crystal is illustrated, namely, to estimate the speed and time of breakdown development, which can be used to interpret the mechanisms of breakdown development.

Electric-field-induced second-harmonic generation using high-intensity femtosecond laser pulses over the observable optical breakdown threshold.

We investigated the performance of electric-field-induced second-harmonic generation (E-FISHG) by spectroscopic measurement using high-intensity femtosecond laser pulses. The second-harmonic intensity increased quadratically versus the applied electric field, as expected from the theory, up to 15 kV/cm with the laser energy up to 2.5 mJ, which is ∼5 times higher than the observable optical breakdown threshold. In addition, when the laser energy was 2.8 mJ, ∼80 times signal intensity at 0.23 mJ was obtained. These results suggest that the electric-field measurement by E-FISHG with high-intensity second harmonics is expected by using high-intensity laser pulses above the observable optical breakdown threshold. Spectroscopic measurement shows no E-FISHG of white light generated by self-phase modulation in laser-induced filament.

Three-dimensional hybrid optoacoustic imaging of the laser-induced plasma and deposited energy density under optical breakdown in water

We report on a hybrid optoacoustic method aimed to retrieve the three-dimensional spatial distributions of the plasma electron density and the deposited energy density in the region of plasma formation under optical breakdown in condensed medium. The spatial distribution of the plasma electron density obtained by the proposed method with the accuracy of 3×1018 cm−3 gives the qualitative characterization of the laser pulse propagation in the region of plasma formation. The spatial distribution of the deposited energy density retrieved by the proposed method with the accuracy of 14 J/cm3 provides the quantitative description of the laser impact on the bulk of the medium. The method is based on photoacoustic imaging and shadowgraphy techniques, which have the spatial resolution of 2 μm and 10 μm, respectively. The proposed method can be applied both in the area of technological applications, such as micromachining of transparent materials, and in the field of the fundamental science of laser–matter interaction.

Reflecting petawatt lasers off relativistic plasma mirrors: a realistic path to the Schwinger limit

Abstract The quantum vacuum plays a central role in physics. Quantum electrodynamics (QED) predicts that the properties of the fermionic quantum vacuum can be probed by extremely large electromagnetic fields. The typical field amplitudes required correspond to the onset of the ‘optical breakdown’ of this vacuum, expected at light intensities >4.7×1029 W/cm2. Approaching this ‘Schwinger limit’ would enable testing of major but still unverified predictions of QED. Yet, the Schwinger limit is seven orders of magnitude above the present record in light intensity achieved by high-power lasers. To close this considerable gap, a promising paradigm consists of reflecting these laser beams off a mirror in relativistic motion, to induce a Doppler effect that compresses the light pulse in time down to the attosecond range and converts it to shorter wavelengths, which can then be focused much more tightly than the initial laser light. However, this faces a major experimental hurdle: how to generate such relativistic mirrors? In this article, we explain how this challenge could nowadays be tackled by using so-called ‘relativistic plasma mirrors’. We argue that approaching the Schwinger limit in the coming years by applying this scheme to the latest generation of petawatt-class lasers is a challenging but realistic objective.

Влияние технологии постростовой обработки на порог оптического пробоя монокристалла ZnGeP2

The threshold of optical breakdown of a ZnGeP2 single crystal manufactured by LOK LLC, Russia, was determined, which was W0d =1.8 J / cm2, and the threshold of optical breakdown of a crystal manufactured by Harbin Institute of Technology, China, was also measured, which was W0d =2.1 J/cm2 (at a wavelength of 2,097 microns of laser radiation and a pulse repetition frequency of 10 kHz with a pulse duration of 35 ns).The effect of post-processing of ZnGeP2 single crystals (polishing of working surfaces )is investigated, application of antireflection interference coatings) to the threshold of optical breakdown of the surface of these crystals. It is established that the presence of silicon conglomerates in the interference antireflection coating leads to a decrease in the optical breakdown threshold.

Recent Research and Development Status of Relaxed Optics and Laser Technology: A Review

It is shown that for laser technologies it was necessary to create a new branch of physics: Relaxed Optics (synthesis of methods of the physical optics, quantum electronics, physical chemistry, physics of irreversible phenomena in unitary system). It is allowed to explain complex chain processes of interaction light and matter. Possible applications of Relaxed Optical methods for the modeling of the laser-induced processes phenomena, including laser implantation (surface and subsurface processes), laser-induced optical breakdown (volume processes) and laser annealing of radiation and other defects in solid, are discussed. Perspectives of using these methods for the creation of new laser technologies, including creation new types of optoelectronic devices (heterostructures, diffraction lattices, etc.), resolution the problems of metallurgy, material science, painting, architecture and a building, are analyzed.

Photothermal therapy with silver nanoplates in HeLa cells studied by in situ fluorescence microscopy.

Photothermal therapy (PTT) is a noninvasive treatment for cancer relying on the incorporation of NIR-light absorbing nanomaterials into cells, which upon illumination release heat causing thermally induced cell death. We prove that irradiation of aqueous suspensions of poly(vinylpyrrolidone)-coated silver nanoplates (PVPAgNP) or PVPAgNP in HeLa cells with red or NIR lasers causes a sizeable photothermal effect, which in cells can be visualized with the temperature sensing fluorophore Rhodamine B (RhB) using spinning disk confocal fluorescence microscopy or fluorescence lifetime imaging. Upon red-light irradiation of cells that were incubated with both, RhB and PVPAgNP at concentrations with no adverse effects on cell viability, a substantial heat release is detected. Initiation of cell death by photothermal effect is observed by positive signals of fluorescent markers for early and late apoptosis. Surprisingly, a new nanomaterial-assisted cell killing mode is operating when PVPAgNP-loaded HeLa cells are excited with moderate powers of fs-pulsed NIR light. Small roundish areas are generated with bright and fast (<1 ns) decaying emission, which expand fast and destroy the whole cell in seconds. This characteristic emission is assigned to efficient optical breakdown initiation around the strongly absorbing PVPAgNP leading to plasma formation that spreads fast through the cell.

Propagation of laser-generated shock waves in metals: 3D axisymmetric simulations compared to experiments

This work aims at demonstrating the ability of an acoustic linear code to model the propagation of a shock wave created by a laser impact over a metallic surface. In this process, a high pressure surface level is reached using a ns laser pulse that heats the surface of the material and generates a dense plasma expansion. The pressure reaches few GPa so shock waves are generated and propagate into the bulk of the material. Currently, shock wave propagation is modeled using continuity equations and an ad hoc equation of state for the illuminated material, very limiting because it is numerically intensive. Here, we propose to model the shock wave bulk propagation using a linear acoustic code. A nonlinear surface pressure term, resulting from the laser–matter interaction, is used as a boundary condition. The applied numerical scheme is based on the Virieux scheme, including a fourth order finite difference discretization of the linearized elastomechanical equations. The role of longitudinal and transverse waves and their origins are highlighted. The importance of considering 3D geometries is pointed out. Simulations are finally confronted with experimental results obtained with the Hephaistos Laserlab facility (energy up to 14 J at 532 nm wavelength laser; pulse duration: 7 ns). Illuminations up to the optical breakdown in water are easily achieved with laser focal spots of 5 mm width. Excellent agreement between experiments and simulations is observed for several sets of experimental parameters for titanium, a material of high elastic limit, while limitations are founded for aluminum. The code is available in the MetaData.

Analysis of Acoustic Signals During the Optical Breakdown of Aqueous Solutions of Fe Nanoparticles

The study investigates the spectra of acoustic signals generating during the optical breakdown of colloidal solutions of iron nanoparticles. A characteristic form of the acoustic spectrum has been experimentally established, a distinctive feature of which is the presence of signals from an expanding and collapsing gas bubble. It is shown that the amplitude and area of these acoustic signals depend on the concentration of nanoparticles in the irradiated colloid. The effect of the concentration of nanoparticles on the bubble lifetime corresponding to the time interval between the acoustic spectrum signals corresponding to the birth and cavitation of a gas bubble has been studied.

Water Decomposition Occurring During Laser Breakdown of Aqueous Solutions Containing Individual Gold, Zirconium, Molybdenum, Iron or Nickel Nanoparticles

Generation rates of hydrogen peroxide (H2O2), hydroxyl radicals (•OH), molecular hydrogen (H2), and molecular oxygen (O2) forming during the optical breakdown of aqueous colloidal solutions containing Au, Mo, Zr, Fe, and Ni nanoparticles have been studied. It is shown that the processes occurring during the dissociation of water molecules under the influence of laser breakdown plasma and leading to the formation of various chemical products depend on the material of the nanoparticles present in the colloid. It was found that the highest rates of generation of water decomposition products are observed in aqueous colloidal solutions of Fe and Ni nanoparticles. The use of Au nanoparticles leads to the lowest generation rate. In general, the materials from which the nanoparticles are made, depending on the efficiency of the formation of water decomposition products, are arranged as follows: Ni&amp;gt; Fe&amp;gt; Mo&amp;gt; Zr&amp;gt; Au.

Hypersonic Imaging and Emission Spectroscopy of Hydrogen and Cyanide Following Laser-Induced Optical Breakdown

This work communicates the connection of measured shadowgraphs from optically induced air breakdown with emission spectroscopy in selected gas mixtures. Laser-induced optical breakdown is generated using 850 and 170 mJ, 6 ns pulses at a wavelength of 1064 nm, the shadowgraphs are recorded using time-delayed 5 ns pulses at a wavelength of 532 nm and a digital camera, and emission spectra are recorded for typically a dozen of discrete time-delays from optical breakdown by employing an intensified charge-coupled device. The symmetry of the breakdown event can be viewed as close-to spherical symmetry for time-delays of several 100 ns. Spectroscopic analysis explores well-above hypersonic expansion dynamics using primarily the diatomic molecule cyanide and atomic hydrogen emission spectroscopy. Analysis of the air breakdown and selected gas breakdown events permits the use of Abel inversion for inference of the expanding species distribution. Typically, species are prevalent at higher density near the hypersonically expanding shockwave, measured by tracing cyanide and a specific carbon atomic line. Overall, recorded air breakdown shadowgraphs are indicative of laser-plasma expansion in selected gas mixtures, and optical spectroscopy delivers analytical insight into plasma expansion phenomena.