Optical Breakdown In Water Research Articles

Study of Intense Femtosecond Radiation Scattering during Optical Breakdown of Water

Study of Intense Femtosecond Radiation Scattering during Optical Breakdown of Water

Optical Breakdown on Clusters of Gas Nanobubbles in Water; Possible Applications in Laser Ophthalmology

Here we studied the regimes of optical breakdown in water, stimulated by nanosecond and picosecond laser pulses at a wavelength of 1064 nm. A distinctive feature of our theoretical model, confirmed in experiment, is that in our case the optical breakdown develops on heterogeneous centers-clusters of gas nanobubbles. To the best of our knowledge, this is the first study of the role of clusters of gas nanobubbles in the optical breakdown of liquids that are transparent to pump radiation. In the experiment described in this paper, it was found that when initially degassed water is saturated with dissolved air, the breakdown threshold decreases. A theoretical model describing this phenomenon is suggested. This model includes the development of an electron avalanche inside individual nanobubbles, followed by the stimulated optical coalescence of a nanobubble cluster. According to our estimates, this regime occurs at laser radiation intensities of about 106–107 W/cm2. It is important that at such low intensities the breakdown flash (the basic endpoint of optical breakdown) does not appear due to the deficit of input laser energy. We provide an experimental proof of the coalescence regime, stimulated by a laser pulse in nanosecond range. The experimental threshold of stimulated coalescence is in good agreement with the theoretical estimates. Since the stimulated optical coalescence mode occurs at very low laser intensities, its excitation does not result in mechanical side effects in eye tissues, i.e., a shock wave should not be excited. Note that shock wave always occurs during optical breakdown, which is traditionally excited at intensities of 1012 W/cm2. In our experiment, the generation of a shock wave at such pump intensities was also observed. Since, according to the estimates given in the article, the volume number density of nanobubble clusters in the intraocular fluid can reach 108 cm−3, the excitation of the stimulated optical coalescence mode of nanobubble clusters can be used in ophthalmic surgery, such as laser iridotomy.

Plasma reflectivity behavior under strong subpicosecond excitation of liquids

Emerging laser plasma-based technologies require new knowledge on the optical pump optimization and underlying physics of laser–matter interaction. Plasma in liquid jets is still largely unexplored, although this configuration is actively used as a part of optical devices. Hereby, in this work, we report on the reflectivity-based approach to study the optical properties of the induced plasma and quasi-free electron temporal dynamics. The single-shot experiments provide plasma characteristics relative to the laser pump parameters. A strong angular dependence of the plasma absorptivity, which affects rigorously the reflectivity curve, is demonstrated. Furthermore, twofold higher plasma reflectivity in ethanol is revealed and explained through the theoretical model of ultrashort laser pulse interaction with a thin dielectric surface layer. Finally, the time-resolved fundamental and third harmonic reflection measurements and associated analytical study provide the new insight into the electron density dynamics in the case of optical breakdown in water and ethanol. We believe that these findings are of particular significance for the development of highly efficient plasma-based x rays and THz radiation sources.

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.

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.

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.

Broadband leaky Lamb waves excited by optical breakdown in water.

Optical breakdown of water is used as a sound source to excite a broadband set of leaky Lamb waves in submerged aluminum plates. The source is shown to simultaneously excite guided modes spanning 0.1-5 MHz in frequency and 0-0.8 mm-1 in wavenumber. The measured response overlaps well with dispersion curves for Lamb waves in the plates, revealing strong coupling to both symmetric and antisymmetric modes. The strongest responses arise when a mode's phase velocity approximately equals the plate's compressional wave velocity. These results are shown to arise from an interplay of the sensing geometry, guided wave speeds, and signal processing. Finally, implications for non-contact sensing are discussed.

Theoretical study on femtosecond laser optical breakdown threshold in water mediated by aluminum nanoparticle coated with silica.

A strongly coupled finite element model of the optical breakdown during femtosecond laser pulse interaction, with different morphology of aluminum nanoparticles in water, was developed. This model provided new insight into the optical breakdown dependence on the nanoparticles' morphology and assembly. This model was used to theoretically investigate a 300 fs laser pulse interaction with uncoupled and plasmon coupled aluminum coated silica shell nanoparticles. This study revealed how the nanoparticles' one-dimensional assembly affected the optical breakdown threshold of its surrounding mediums. The optical breakdown threshold had much stronger dependence on the optical near-field enhancement than on the nanostructure's extinction cross-section. The maximum electric field that is outside of the aluminum nanoparticles, with 2 nm silica shell and 2 nm gap, was more than 4 times greater to the one inside of the aluminum nanoparticles. For dimer and trimer configuration, the calculated lattice cross-section temperatures at each breakdown threshold were below their melting point. It is suggested that water could be ionized by aluminum/silica (core/shell) nanostructure during femtosecond laser exposures without nanoparticles consumption. This model could increase understanding of the aluminum nanoparticle-mediated optical breakdown in water.

Optical breakdown as a broadband underwater acoustic source

Current underwater transducers provide little support for remote measurement of material properties. Such measurements are often limited by high impedance contrast, and target inhomogeneities that arise from biofouling and corrosion. In the presence of these limitations, a sensing system would benefit from broadband, spatially-localized target excitation. The high bandwidth would allow a return signal to encode broader information content about the target, while spatial localization would provide stronger target excitation and higher spatial resolution for measurements. Although these source properties are not achievable with traditional transducer designs, they can be produced through laser-induced optical breakdown in water. During optical breakdown, focused laser light excites a localized plasma, which expands and produces a mechanical shock wave. The shock properties are set by both the medium hydrodynamics and the laser parameters, allowing the acoustic source to be optically tuned. In laboratory experiments, breakdown from a 4 mJ/ 4ns laser pulse emits an exponential pressure wave with a decay constant under 250 ns and peak pressure near 600 kPa at 2 cm range. Here, I discuss the physics and fundamental limitations of acoustic transduction via underwater optical breakdown. Experimental results illustrate how the acoustic source properties can be tuned through optical control.

Adaptive optics assisted and optical coherence tomography guided fs-laser system for ophthalmic surgery in the posterior eye.

While fs-lasers are clinically established for surgery in the anterior eye, their use in the posterior eye is impeded by aberrations and focus position errors. We implemented a laboratory system to investigate whether fs-laser surgery in the posterior eye is made more feasible by aberration correction and tomographic image guidance. Aberration correction is obtained by adaptive optics (AO) and the image guidance is accomplished by optical coherence tomography (OCT). System characteristic measurements and cutting experiments were performed inside an eye model. By aberration correction, wavefront errors were reduced from 270 nm root-mean-square (rms) to 64 nm rms, ignoring Zernike terms for tilts and focus. The Strehl ratio of the assigned point spread function is improved from 0.11 to 0.78. The threshold pulse energy of laser-induced optical breakdown in water is lowered from about 3.0 to about 1.3???J measured at the eye model entrance. After laser cutting of a synthetic foil placed 300???m in front of porcine retinal tissue with the corrected system, postoperative three-dimensional OCT imaging showed no lesions in the tissue. Our results corroborate that AO and OCT will be two essential assistive components for possible clinical systems for fs-laser–based surgery in the posterior eye.

Wavelength dependence of femtosecond laser-induced breakdown in water and implications for laser surgery

The wavelength dependence of the threshold for femtosecond optical breakdown in water provides information on the interplay of multiphoton, tunneling, and avalanche ionization and is of interest for parameter selection in laser surgery. We measured the bubble threshold from ultraviolet to near-infrared wavelengths and found a continuous decrease of the irradiance threshold with increasing wavelength $\ensuremath{\lambda}$. Results are compared to the predictions of a numerical model that assumes a band gap of 9.5 eV and considers the existence of a separate initiation channel via excitation of valence band electrons into a solvated state followed by rapid upconversion into the conduction band. Fits to experimental data yield an electron collision time of $\ensuremath{\approx}1\phantom{\rule{0.16em}{0ex}}\mathrm{fs}$ and an estimate for the capacity of the initiation channel. Using that collision time, the breakdown dynamics were explored up to $\ensuremath{\lambda}=2\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}$. The irradiance threshold first continues to decrease but levels out for wavelengths longer than 1.3 $\ensuremath{\mu}\mathrm{m}$. This opens promising perspectives for laser surgery at wavelengths around 1.3 and 1.7 $\ensuremath{\mu}\mathrm{m}$, which are attractive because of their large penetration depth into scattering tissues.

Wavelength dependence of nanosecond infrared laser-induced breakdown in water: Evidence for multiphoton initiation via an intermediate state

Abstract : Investigation of the wavelength dependence (725 1025 nm) of the threshold for nanosecond optical breakdown in water revealed steps consistent with breakdown initiation by multiphoton ionization, with an initiation energy of about 6.6 eV. This value is considerably smaller than the autoionization threshold of about 9.5 eV, which can be regarded as band gap relevant for avalanche ionization. Breakdown initiation is likely to occur via excitation of a valence band electron into a solvated state, followed by rapid excitation into the conduction band. Theoretical analysis based on these assumptions suggests that the seed electron density required for initiating avalanche ionization drops from 2.51015 cm-3 at 725 nm to 1.11012 cm-3 at 1025 nm. These results demand changes of future breakdown modeling for water including the use of a larger band gap than previously employed, the introduction of an intermediate energy level for initiation, and consideration of the wavelength dependence of seed electron density.

Pulsed laser induced microbubble in gold nanorod colloid

The characterization of a pulsed laser induced microbubble (PLIMB) in gold nanorod (GNR) colloid was studied experimentally. The generation of PLIMB is due to the optical breakdown in water. Using an ultrasonic transducer and a probing He–Ne laser associated with a photodetector, the photoacoustic (PA) signals and the bubble formation of the multi-cycled oscillation of a single PLIMB were measured simultaneously. Both results are in agreement to show that the lifetime of PLIMB is reduced as the gold concentration increases. This phenomenon is attributed to the plasmonic light scattering (Faraday–Tyndall effect) in GNR colloid; the energy for optical breakdown is reduced at the focus due to laser-beam defocusing. The effect is particularly pronounced at the longitudinal surface plasmon resonance of GNRs. In addition, the divergence angle of 532-nm CW laser beam through gold nanoparticle (GNP) colloid was measured. Our results show that the divergence angle increases as the concentration of GNP increases. This phenomenon again elucidates Faraday–Tyndall effect.

Laser-induced fluorescence of uranyl complexes in aqueous solutions: the role of diffusion-controlled excited states annihilation

We present the analysis of diffusion-controlled annihilation of excited U(VI) complexes in aqueous media that leads to appearance of rapid non-exponential fluorescence decay. We show that under typical experimental conditions the impact of annihilation processes can't be neglected when determining U(VI) complexes fluorescence lifetimes: at excitation intensities between 10(6) W/cm(2) and 10(8) W/cm(2), the rate of excited states deactivation increases, and then an opposite trend is observed. The latter can be interpreted as the consequence of optical breakdown in water.

Experimental Investigation on Underwater Opto-Acoustic Communication

The underwater opto-acoustic communication system for directional acoustic communication between an in-air platform and a submerged platform operating is important. The paper presents a new method to solve this problem with opto-acoustic technology, which combines high-energy laser, the opto-acoustic transmitter that optical energy is converted to acoustic energy at the water surface. The laser-based transmitter provides a versatile method for generating underwater sound. The acoustic pressure is linearly proportional to the laser power. The paper designed an experimental measurement system for the opto-acoustic communication. It made experiments for study on the waveform and spectrum characteristics of opto-acoustic signals. The paper also discuss the acoustic wave after optical breakdown in water with Nd:YAG laser pulses. The opto-acoustic signals can controll by adjusting the laser's parameters. The conclusion is that the opto-acoustic communication has some technical advantages. This system presents a change in the way communicational from the air.

Optical breakdown in transparent media with adjustable axial length and location

We demonstrate a highly elongated (aspect ratio over 500:1) optical breakdown in water produced by a single pulse of a picosecond laser focused with a combination of an axicon and a lens. Locations of the proximal and distal ends of the breakdown region can be adjusted by modifying radial intensity distribution of the incident beam with an amplitude mask. Using Fresnel diffraction theory we derive a transmission profile of the amplitude mask to create a uniform axial intensity distribution in the breakdown zone. Experimentally observed dynamics of the bubbles obtained with the designed mask is in agreement with the theoretical model. A system producing an adjustable cylindrical breakdown can be applied to fast linear or planar dissection of transparent materials. It might be useful for ophthalmic surgical applications including cataract surgery and crystalline lens softening.

Role of Dissolved Gas in Optical Breakdown of Water: Differences between Effects Due to Helium and Other Gases

It is shown that water contains defects in the form of heterogeneous optical breakdown centers. Long-living complexes composed of gas and liquid molecules may serve as nuclei for such centers. A new technique for removing dissolved gas from water is developed. It is based on a "helium washing" routine. The structure of helium-washed water is very different from that of water containing dissolved atmospheric gas. It is able to withstand higher optical intensities and temperatures of superheating compared with the nonprocessed ones. The characteristics of plasma spark and values of the breakdown thresholds for processed and nonprocessed samples are given.

飞秒激光诱导水光学击穿阈值

For studying the relationship between breakdown thresholds and laser parameters, numerical simulation for ellipsoidal time and space model of femtosecond laser-induced optical breakdown in water was done at different pulse duration (40 fs to 540 fs), wavelength (400 nm to 1 200 nm) and spot size (0 to 200 μm) with a Runge-Kutta method. The figures of threshold intensity as a function of pulse duration, wavelength or spot size were given via variable-controlled method. Some conclusions were presented about the relationship between threshold intensity and laser parameters. At last, the figures of threshold power, energy, radiant exposure or electric field strength as a function of pulse duration, wavelength or spot size were presented, which gives a further theoretical support for the study

Interaction dynamics of spatially separated cavitation bubbles in water

We present a high-speed photographic analysis of the interaction of cavitation bubbles generated in two spatially separated regions by femtosecond laser-induced optical breakdown in water. Depending on the relative energies of the femtosecond laser pulses and their spatial separation, different kinds of interactions, such as a flattening and deformation of the bubbles, asymmetric water flows, and jet formation were observed. The results presented have a strong impact on understanding and optimizing the cutting effect of modern femtosecond lasers with high repetition rates (>1 MHz).

Multiphoton optical breakdown in water under picosecond laser pulses

The phenomenon of optical breakdown in highly purified (free of external impurities and bubstons) water under picosecond laser excitation was experimentally investigated. Narrow-band UV flashes were revealed. This effectmakes it possible to distinguish themodes of optical breakdown occurring either through multiphoton ionization of water molecules or via impact ionization at heterogeneous seeds.