Single bubble sonoluminescence and stable cavitation

A single bubble trapped at an antinode of an acoustic standing wave field in water can emit 50ps-140ps light pulses, called “single bubble sonoluminescence” (SBSL). It arouses much interest in physical acoustics because of its highly non-linear characteristics, high concentration of energy, and stable cavitation behavior. In this paper, bubble stability, the dynamic behavior of bubbles, non-invasive measurement of driving acoustic pressure and Mie scattering method are introduced.

The characteristics of sonoluminescence

Cavitation luminescence is light emission from gases that are compressed to high temperature and high pressure inside a bubble or group of bubbles. The numerical simulation in this study indicates that if the temperature and pressure inside a bubble are not high enough, then dim and spectral line emission dominates. However, if the temperature and pressure inside the bubble are very high, then the light is bright and a continuum spectrum will be generated. Calculations of the spectrum using modified equations of bubble motion can simulate the spectral profile well. However, pulse width calculations using these equations only partly agree with the experimental results.

Comparison of Xe single bubble sonoluminescence in water and sulfuric acid

Using the equations of fluid mechanics with proper boundary conditions and taking account of the gas properties, we can numerically simulate the process of single bubble sonoluminescence, in which electron-neutral atom bremsstrahlung, electron-ion bremsstrahlung and recombination radiation, and the radiative attachment of electrons to atoms and molecules contribute to the light emission. The calculation can quantitatively or qualitatively interpret the experimental results. We find that the accumulated heat energy inside the compressed gas bubble is mostly consumed by the chemical reaction, therefore, the maximum degree of ionization inside Xe bubble in water is much lower than that in sulfuric acid, of which the vapour pressure is very low. In addition, in sulfuric acid much larger pa and R0 are allowed which makes the bubbles in it much brighter than that in water.

Computation and analysis of light emission in two-bubble sonoluminescence

We perform a computational simulation of light emissions from two sonoluminescent bubbles in water. Our simulation includes the radii of two bubbles, radiation acoustic pressures, and light emission spectra by numerically solving the pulsing equations of a two-bubble system and the equations of gas dynamics. The simulation results demonstrate that the motion of each bubble in the two-bubble system is restrained because of the radiation acoustic pressures from the other pulsing bubble. The restrained oscillation of a bubble with a small ambient radius is stronger than that of a bubble with a large ambient radius under the same driving acoustic pressure. This effect increases when the distance between the two bubbles decreases. When compared to single-bubble sonoluminescence, the interaction between two bubbles leads to generation of different spectral characteristics.

Sonoluminescence as the PeTa Radiation

In this paper, a model of cavitational luminescence (CL) and sonoluminescence (SL) is developed. The basis of the model is the PeTa (Perel’man-Tatartchenko) effect—a characteristic radiation under first-order phase transitions. The main role is given to the liquid, which is where the cavitation occurs. The evaporation of the liquid and subsequent vapor condensation inside the bubble are responsible for the CL and SL. Apparently, the dissolved gases and other impurities in the liquid are responsible for peaks that appear at the background of the main spectrum. They most likely are excited by a shock wave occurred during cavitation. The model explains the main experimental data. Thus, no mystery, no plasma, no Hollywood.

Sonoluminescence as the PeTa Radiation, Part Three

This paper is the third in a series published in this journal during 2017-2018. These three papers present various stages in the development of the PeTa model for phenomena of the same physical nature: cavitational luminescence (CL), multi-bubble sonoluminescence (MBSL), single-bubble sonoluminescence (SBSL), and laser-induced bubble luminescence (LIBL). The basis of this model is the PeTa (Perel’man-Tatartchenko) effect—a nonequilibrium characteristic radiation under first-order phase transitions, for instance, vapour condensation. The third iteration of this model “Vapour bubble luminescence” (VBL) is presented in this paper. The essence of this model is as follows: with a local decrease of pressure or an increase of temperature in a tiny volume of the liquid, one or several bubbles filled with vapour will appear. Subsequently, a very rapid increase in pressure or a decrease in temperature of the bubble leads to super-saturation of the vapour inside the bubble, followed by its instantaneous condensation with the emission of condensation energy (this is the PeTa effect). A sharp decrease in pressure causes the collapse of the bubble accompanied by a shock wave in the liquid. VBL model is conveniently represented on the solid-liquid-vapour phase diagram. A better understanding of the physical nature of the phenomena under consideration could help to find their useful applications. To develop this idea further, we propose a design of a cavity-free pulsed laser on the basis of CL/MBSL/SBSL. An analysis of LIBL in cryogenic liquids is also given in this paper.

Sonoluminescence as the PeTa Radiation, Part Two

This paper is a continuation of one published in this journal nine months ago. The two papers present a model of cavitational luminescence (CL), multi-bubble sonoluminescence (MBSL), one-bubble sonoluminescence (OBSL), and laser-induced bubble luminescence (LIBL). The basis of this model is the PeTa (Perel’man-Tatartchenko) effect, a nonequilibrium characteristic radiation under first-order phase transitions, especially vapour condensation. In this model, the main role is given to the liquid, where the evaporation, condensation, flash, and subsequent collapse of bubbles occur. The instantaneous vapour condensation inside the bubble is a reason for the CL/MBSL/OBSL/LIBL. Apparently, the dissolved gases and other impurities in the liquid are responsible for peaks that appear at the background of the main spectrum. They are most likely excited by a shock wave occurred during the collapse. This paper, in contrast to the previous one, presents a slightly expanded model that explains additional experimental data concerning especially the LIBL spectrum. As a result, today we are not aware of any experimental data that would contradict the PeTa model, and we continue to assert that there is no mystery to the CL/MBSL/OBSL/LIBL phenomena, as well as no reason to hope that they can be used for high-temperature chemical reactions, and even more so for a thermonuclear ones.

A unique circular path of moving single bubble sonoluminescence in water

Based on a quasi-adiabatic model, the parameters of the bubble interior for a moving single bubble sonoluminescence （m-SBSL） in water are calculated. By using a complete form of the hydrodynamic force, a unique circular path for the m-SBSL in water is obtained. The effect of the ambient pressure variation on the bubble trajectory is also investigated. It is concluded that as the ambient pressure increases, the bubble moves along a circular path with a larger radius and all bubble parameters, such as gas pressure, interior temperature and light intensity, increase. A comparison is made between the parameters of the moving bubble in water and those in N-methylformamide. With fluid viscosity increasing, the circular path changes into an elliptic form and the light intensity increases.

Computational simulation of ionization processes in single-bubble and multi-bubble sonoluminescence

The most recent spectroscopic studies of moving-single bubble sonoluminescence(MSBSL)and multi-bubble sonoluminescence(MBSL)have revealed that hydrated electrons(e^(-)_(aq))are generated in MSBSL but absent in MBSL.To explore the mechanism of this phenomenon,we numerically simulate the ionization processes in single-and multi-bubble sonoluminescence in aqueous solution of terbium chloride(TbCl_(3)).The results show that the maximum degree of ionization of single-bubble sonoluminescence(SBSL)is approximately 10000 times greater than that of MBSL under certain special physical parameters.The hydrated electrons(e^(-)_(aq))formed in SBSL are far more than those in MBSL provided these electrons are ejected from a bubble into a liquid.Therefore,the quenching of e^(-)_(aq)to SBSL spectrum is stronger than that of the MBSL spectrum.This may be the reason that the trivalent terbium[Tb(Ⅲ)]ion line intensities from SBSL in the TbCl_(3) aqueous solutions with the acceptor of e^(-)_(aq)are stronger than those of TbCl_(3) aqueous solutions without the acceptor of e^(-)_(aq).Whereas the Tb(Ⅲ)ion line intensities from MBSL are not variational,which is significant for exploring the mechanism behind the cavitation and sonoluminescence.

Abnormal ionization in sonoluminescence

Sonoluminescence is a complex phenomenon, the mechanism of which remains unclear. The present study reveals that an abnormal ionization process is likely to be present in the sonoluminescing bubble. To fit the experimental data of previous studies, we assume that the ionization energies of the molecules and atoms in the bubble decrease as the gas density increases and that the decrease of the ionization energy reaches about 60%-70% as the bubble flashes, which is difficult to explain by using previous models.

On a Heuristic Viewpoint Concerning the Conversion and Transformation of Sound into Light

In the study of Terrestrial Gamma-ray Flashes (TGFs) and Sonoluminescence, we observe parallels with larger cosmic events. Specifically, sonoluminescence involves the rapid collapse of bubbles, which closely resembles gravitational collapse in space. This observation suggests the potential formation of low-density quantum black holes. These entities, which might be related to dark matter, are thought to experience a kind of transient evaporation similar to Hawking radiation seen in cosmic black holes. Consequently, sonoluminescence could be a valuable tool for investigating phenomena typically linked to cosmic scale events. Furthermore, the role of the Higgs boson is considered in this context, possibly connecting it to both TGFs and sonoluminescence. This research could enhance our understanding of the quantum mechanics of black holes and their relation to dark matter on Earth.

Comparison between the single-bubble sonoluminescences in sulfuric acid and in water

Single-bubble sonoluminescence (SBSL) is achieved with strong stability in sulfuric acid solutions. Bubble dynamics and the SBSL spectroscopy in the sulfuric acid solutions with different concentra- tions are studied with phase-locked integral stroboscopic photography method and a spectrograph, respectively. The experimental results are compared with those in water. The SBSL in sulfuric acid is brighter than that in water. One of the most important reasons for that is the larger viscosity of sulfuric acid, which results in the larger ambient radius and thus the more contents of luminous material inside the bubble. However, sonoluminescence bubble’s collapse in sulfuric acid is less violent than that in water, and the corresponding blackbody radiation temperature of the SBSL in sulfuric acid is lower than that in water.

Dynamic behavior of gas bubble in single bubble sonoluminescence—vibrator model

Single bubble sonoluminescence is a process of energy transformation from sound to light. Therefore the motion equations of near spherical vibration of a gas bubble in an incompressible and viscous liquid can be deduced by Lagrangian Equation with dissipation function when the bubble is considered as a vibrator surrounded by liquid. The analytical solutions in the bubble expanding, collapsing and rebounding stages can be obtained by solving these motion equations when some approximations are adopted. And the dynamic behaviors of the bubble in these three stages are discussed.

Calculation of light emission in sonoluminescence

We modify a uniform model of single bubble sonoluminescence,in which heat diffusion,water vapor diffusion and chemical reactions are included to describe the bubble dynamics,and the processes of electron-atom bremsstrahlung,electron-ion bremsstrahlung and recombination radiation,radiative attachment of electrons to atoms and molecules,line emissions of OH radicals and Na atoms are taken into account to calculate the light emission. With this model,we compute the light pulse width,the photon number per flash,the continuum and line spectra and the gas species as the products of chemical reactions,and try to compare with all the experimental data available. We obtain good agreement with the observations of Ar and Xe bubbles in many cases,but fail to match the experimental data of the photon number per flash. We also find that for He bubble the computed photon number is always too small to interpret the observations.

Sonoluminescence of luminol-sodium carbonate solution

The authors have taken the photo of a prcsct paper-cut figure with ordinary film exposed to the sonoluminescence of aqueous solution of luminol-sodium carbonate, and also obtained the sonoluminescence spectrum and photo-fluorescence spectrum of this solution. These results show that the wavelengths of the enhanced sonoluminescence by luminol in this solution are mainly in the visible region. In respect to the cmission wavelengths, there is a certain equivalency between the sonoexcitation and photoexcitation.

Finite-amplitude vibration of a bubble in water

The numerical results obtained by Rayleigh-Plesset （R-P） equation failed to agree with the experimental Mie scattering data of a bubble in water without inappropriately increasing the shear viscosity and decreasing the surface tension coefficient. In this paper, a new equation proposed by the present authors （Qian and Xiao） is solved. Numerical solutions obtained by using the symbolic computation program from both the R-P equation and the Qian-Xiao （Q-X） equation clearly demonstrate that Q-X equation yields best results matching the experimental data （in expansion phase）. The numerical solutions of R-P equation also demonstrate the oscillation of a bubble in water depends strongly upon the surface tension and the shear viscosity coefficients as well as the amplitude of driving pressure, so that the uniqueness of the numerical solutions may be suspected if they are varied arbitrarily in order to fit the experimental data. If the bubble＇s vibration accompanies an energy loss such as the light radiation during the contract phase, the mechanism of the energy loss has to be taken into account. We suggest that by use of the bubble＇s vibration to investigate the state equations of aqueous solutions seem to be possible. We also believe that if one uses this equation instead of R-P equation to deal with the relevant problems such as the ＇phase diagrams for sonoluminescing bubbles＇, etc., some different results may be expected.

Investigation of a mutual interaction force at different pressure amplitudes in sulfuric acid

This paper investiages the secondary Bjerknes force for two oscillating bubbles in various pressure amplitudes in a concentration of 95% sulfuric acid. The equilibrium radii of the bubbles are assumed to be smaller than 10 μm at a frequency of 37 kHz in various strong driving acoustical fields around 2.0 bars （1 bar=10^5 Pa）. The secondary Bjerknes force is investigated in uncoupled and coupled states between the bubbles, with regard to the quasi-adiabatic model for the bubble interior. It finds that the value of the secondary Bjerknes force depends on the driven pressure of sulfuric acid and its amount would be increased by liquid pressure amplitude enhancement. The results show that the repulsion area of the interaction force would be increased by increasing the driven pressure because of nonlinear oscillation of bubbles.

Conical bubble photoluminescence from rhodamine 6G in 1, 2-propanediol

A modified U-tube conical bubble sonoluminescence device is used to study the conical bubble photoluminescence. The spectra of conical bubble sonoluminescence at different concentrations of rhodamine 6G （Rh6G） solution in 1,2- propanediol have been measured. Results show that the sonoluminescence from the conical bubbles can directly excite Rh6G, which in turn can fluoresce. The light emission of this kind is referred to as conical bubble photoluminescence. The maximum of fluorescence spectral line intensity in the conical bubble photoluminescence has a red shift in relative to that of the standard photo-excited fluorescence, which is due to the higher self-absorption of Rh6G, and the spectral line of conical bubble photoluminescence is broadened in width compared with that of photo-excited fluorescence.

Bubble Glow at Hydrothermal Vents as the <i>PeTa</i>Radiation

The paper presents a physical model of a natural phenomenon, the glow of bubbles at hydrothermal vents formed during underwater volcanic activity. The basis of the model is characteristic non-equilibrium radiation under first order phase transitions that since 2010 has been referred to as the PeTa (Perelman-Tatartchenko) effect. This is the fourth paper in a series developing the model for similar physical phenomena: cavitational luminescence (CL), multi-bubble sonoluminescence (MBSL), single-bubble sonoluminescence (SBSL) and laser-induced bubble luminescence (LIBL). The previous three papers were published during 2017-2018 in this Journal. In the third one we have shown that above mentioned physical effects can be generalized as a phenomenon that we have titled “Vapour bubble luminescence” (VBL). VBL is very clearly represented in a non-equilibrium phase diagram. The essence of VBL is as follows: when there is a local decrease in pressure and/or an increase of temperature in a tiny volume of a liquid occurs, one or several bubbles filled with vapour will appear. Subsequently a very rapid pressure increase and/or temperature decrease in the same volume of liquid leads to supersaturation of the vapour inside the bubble. Upon reaching critical vapor density, instantaneous vapour condensation and emission of the phase transition energy that is accompanied by a flash (this is the PeTa effect) results in a sharp pressure decrease and the bubble collapses due to the pressure drop. This process is accompanied by a shock wave in the liquid. A similar effect occurs if bubbles filled with hot steam, for example from a cappuccino machine, are injected into a relatively large volume of cold water. The VBL model explains all experimental data concerning CL/MBSL/SBSL/LIBL and the relatively new natural phenomenon, the glow of bubbles at hydrothermal vents. Several model experiments demonstrate the PeTa effect under similar conditions. Additionally, we define the PeTa effect in all its manifestations on a non-equilibrium phase diagram. This clarifies which niches can contain VBL processes. We also demonstrate the window of transparency (WT) for the PeTa radiation during crystallization of a supercooled tellurium melt and propose the design of a cavity-free pulsed laser on the basis of similar crystallization processes.

Dynamics and measurement of cavitation bubble

Based on the introduction of international progress, our investigations on acoustic cavitation have been reported. Firstly we considered the cavity's dynamics under the drive of the asymmetrical acoustic pressure. An aspheric dynamical model was proposed and a new stable and aspheric solution was found in numerical simulation of the theoretical framework of the aspheric model. Then, a dual Mie-scattering technique was developed to measure the cavity's aspheric pulsation. A significant asynchronous pulsation signal between two Mie-scattering channels was caught in the case of large cavity driven by low acoustic pressure. As a direct deduction, we observed an evidence of cavity's aspheric pulsation. Furthermore, we studied the dependency of the asynchronous pulsation signal on the various parameters, such as the amplitude and frequency of the driving acoustic pressure, and the surface tension, viscosity and gas concentration of the liquid. Finally, we introduced a new numeric imaging technique to measure the shapes of the periodic pulsation cavities. The time-resolution was in the order of 20 ns, one order of magnitude lower than that in the previous work, say, 200 ns.