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Light Sources
Published in Toru Yoshizawa, Handbook of Optical Metrology, 2015
Sonoluminescence is the emission of short bursts of light from a gaseous cavity (bubbles) induced in a liquid by high-intensity sound [71,72]. The light emission occurs when the bubbles quickly collapse and reach minimum size. Sonoluminescence can be observed from clouds of bubbles and, under certain circumstances, from a single bubble [73–76]. The bubble may already exist in the liquid or may be created through cavitation, the process of formation, growth, and collapse of bubbles under the influence of high-intensity sound or ultrasound. A single bubble can be trapped at a pressure antinode of the acoustic standing wave formed in the liquid. It will periodically expand and collapse, emitting a flash of light each time it collapses. Single-bubble flashes can have very stable periods and positions. The resonant frequencies depend on the shape and size of the container. The light pulses from the bubbles are extremely short (between 35 and a few hundred picoseconds) [76]. Adding a small amount of noble gas (helium, argon, or xenon) to the gas in the bubble increases the intensity of the emitted light. The collapsed bubbles are about 1 μm in diameter depending on the ambient fluid (e.g., water) and on the gas content of the bubble (e.g., atmospheric air). When the bubble collapses, the pressure increases significantly and the temperature in the interior of the bubble can reach around 10,000 K. This causes ionization of the noble gas present in the bubble [74]. Such high temperatures provide conditions for thermonuclear fusion. This possibility makes sonoluminescence especially interesting subject for investigation [77].
Conclusion
Published in Dmitry A. Biryukov, Denis N. Gerasimov, Eugeny I. Yutin, Cavitation and Associated Phenomena, 2021
Dmitry A. Biryukov, Denis N. Gerasimov, Eugeny I. Yutin
The physical nature of sonoluminescence is unclear. The main set of explanations aims rather at the description of conditions that may cause some light emission and does not account for certain details of the given specific glow. Today, the main cause of sonoluminescence is assumed to be high temperature inside a bubble during its collapse, but this theory cannot point out all the intermediates in the chain from the bubble collapse to the light emission. The main competitor of this theory supposes electrical effects during the bubble collapse; generally, such approach does not explain all the features of that light too.
Applications of Ultrasonics Based on Chemical Effects—Sonochemistry
Published in Dale Ensminger, Leonard J. Bond, Ultrasonics, 2011
Dale Ensminger, Leonard J. Bond
Sonoluminescence is extremely sensitive to a complex set of external parameters, which has hindered its more widespread use as an analytical method. However, advancements in this area continue and are discussed in Chapter 11.
Liquid compressibility effect on the acoustic generation of free radicals
Published in Journal of Applied Water Engineering and Research, 2020
Slimane Merouani, Oualid Hamdaoui, Nassim Kerabchi
The basic underlying phenomenon behind the effects of ultrasound in aqueous systems, whether physical, chemical, or biological, is acoustic cavitation (Bhangu and Ashokkumar 2016). The word cavitation refers to the formation, growth and collapse of vapor/gas bubbles in liquids subjected to power ultrasound (frequency: 20–1000 kHz) (Leighton 1994). Depending on the frequency and intensity of the ultrasound wave, the bubbles can undergo either a stable, oscillatory motion for several acoustic cycles or a transient motion comprising a single growth and collapse phase in one or less than one acoustic cycle (Thompson and Doraiswamy 1999). On collapse, the transient cavitation bubbles produce very high temperatures and pressures therein (∼ 5000 K and up to 700 atm) (Didenko et al. 1999; Suslick et al. 1999; McNamara et al. 2003; Rae et al. 2005; Ashokkumar 2011; Suslick et al. 2011; Merouani et al. 2014a), which are responsible for all observed effects of ultrasound, such as erosion, sonoluminescence, sonochemistry, etc. In aqueous solution, water vapor trapped inside the bubble dissociates into H• and •OH radicals which then conduct a reaction chain inside the bubble to yield other reactive species, i.e. HO2•, O and O3 (Yasui et al. 2005). These radical species are the origin of the chemical effect of ultrasound (Adewuyi 2001). Radical’s recombination yields hydrogen peroxide and hydrogen, which are the major products of water sonolysis (Merouani et al. 2010; Merouani et al. 2015).
Relationship between liquid depth and the acoustic generation of hydrogen: design aspect for large cavitational reactors with special focus on the role of the wave attenuation
Published in International Journal of Green Energy, 2019
Nassim Kerabchi, Slimane Merouani, Oualid Hamdaoui
Sonochemical reaction generates hydrogen through acoustic cavitation event (Merouani et al. 2015b, 2016b). Acoustic cavitation, the formation, growth, and implosive collapse of millions of microbubbles, is the result of pressure variation in a liquid when high-frequency ultrasound waves (20 kHz to 1 MHz) pass through it. During the compression cycle, the average distance between the molecules decreases, while during the rarefaction cycle, it increases. If a sufficiently large negative pressure is applied to the liquid so that the average distance between the molecules exceeds the critical molecular distance required to hold the liquid intact, cavities can be created (Leighton 1994). Cavities first grow in size until the maximum of the negative pressure is reached, and in the succeeding compression cycle, they contract and collapse violently on a very short time scale (estimated to 1/3 cycle) (Leighton 1994), resulting in transient temperatures of at least 5000 K, and pressures up to 1000 atm in the residual bubble (Suslick and Flannigan 2008), followed by very fast cooling rate (1012 K/s) (Flint and Suslick 1991). Consequently, under these extreme conditions, water vapor/gases and sufficiently volatile molecules vaporized into the gas phase thermalyzed to free radicals and atoms (·OH, H·, O, HO2…). The propagation of the reaction chain inside the bubble leads to the formation of hydrogen, as the most quantifiable gas product of water sonolysis, particularly for argon-saturated water (Anbar and Pecht 1964; Fischer, Hart, and Henglein 1986a, 1986b; Hart, Fischer, and Henglein 1986; Hart and Henglein 1987). The collapse of the bubbles also generates shock waves and emits light (sonoluminescence), which is recently used as a probe for determining several aspects of acoustic bubbles (temperature, pressure, size of active bubbles, etc.) (Brotchie, Grieser, and Ashokkumar 2009; Didenko, McNamara, and Suslick 1999; McNamara III et al. 2003; Zakin et al. 1996).