Comparison of Multibubble and Single-Bubble Sonoluminescence Spectra

Abstract

Comparisons of the spectral characteristics of sonoluminescence from cavitation in bubble fields (MBSL) versus cavitation of single bubbles (SBSL) have been made for aqueous solutions under similar experimental conditions. In particular, alkali metal chloride solutions exhibit sonoluminescence emission from excited state Na or K atoms in MBSL, while SBSL exhibits no such emission. Since the metal ions are not volatile, participation of the initially liquid phase must occur in MBSL. Surface wave and microjet formation in cavitating bubble fields versus the high spherical symmetry of collapse of an isolated bubble may account for the observed differences.PACS numbers: 78.60. Mq, 43.25.+y, 47.40.Nm It has long been known that under certain conditions acoustic irradiation of a liquid can result in light emission, a phenomenon called sonoluminescence (SL) [1,2].The process typically involves the application of high intensity ultrasound to a liquid by an immersed acoustic horn driven with a piezoelectric transducer. The resulting cavitation-bubble field is made up of a complex distribution of gas and vapor-filled bubbles of various equilibrium sizes that pulsate at various phases relative to the driving acoustic pressure field. The bubble dynamics is further complicated by interactions with neighboring bubbles [3] as well as with the vessel walls. Depending on the location within the pressure field and these other infIuences, some of the bubbles may grow dramatically during the negative portion of the sound field, followed by a quasiadiabatic collapse that results in the heating of the bubble interior and the subsequent emission of light [4].In spite of the complexity of cavitating bubble fields, many studies have been made of multibubble sonoluminescence (MBSL) and the influences of fluid and gas properties. The optical spectra of MBSL typically contains distinct, pressure broadened molecular or atomic emission bands. Of particular significance here is the identification of individual transitions from excited states of diatomic carbon (Cq) that contribute to the optical spectrum of MBSL in nonaqueous liquids. The fitting of the measured spectrum of C2 permitted the measurement of an effective rotational and vibrational temperature of the excited states of Cq of 5100 K [5].Recent experimental advances [6] have also made it possible to examine both the temporal and spectral nature of sonoluminescence from a single bubble (SBSL). Here a single bubble is acoustically levitated in an aqueous solution that has been partially degassed. The bubble can be made to undergo large-amplitude, nonlinear, presumably radial pulsations during which light emission can occur. Some properties of SBSLinclude [7] the synchronous emission of light with each and every acoustic cycle, tem-poral flash widths of less than 50 ps, and a continuous spectral energy density that increases from the visible into the UV, with eventual fall off due to UV absorption by the surrounding water. In addition, unlike in MBSL, there are little or no electroni...

Analysis of Rayleigh–Plesset dynamics for sonoluminescing bubbles

“…The standing ultrasound wave of the driving keeps the bubble in position at a pressure antinode and, at the same time, drives its oscillations. The experiments of Putterman's group (Barber & Putterman 1991;Barber et al (1994Barber et al ( , 1995; Hiller et al 1994;Löfstedt, Barber & Putterman 1993;Weninger, Putterman & Barber 1996) and others have revealed a multitude of interesting facts about SBSL: the width of the light pulse is small (Barber & Putterman 1991 give 50 ps as upper threshold, Moran et al 1995 10 ps -recent measurements by Gompf et al 1997 report 100-300 ps, depending on the forcing pressure and gas concentration in the liquid), the spectrum shows no features such as lines (Hiller, Putterman & Barber 1992;Matula et al 1995). While the exact mechanism of light emission is still an open issue, almost all suggested theories -see e.g.…”

Inverse Analysis of Cavitation Impact Phenomena on Structures

“…The complete photoemission spectrum associated with cavitation bubble collapse in water has yet to be determined. Previous studies showed only broad emission bands in the visible region of the electromagnetic wave spectrum characterized by the absence of any spectral peaks (17)(18)(19)(20)(21). The intensity of these spectra appears to increase continuously with frequency until the UV cutoff of water at 200 nm (18,21).…”

“…The intensity of these spectra appears to increase continuously with frequency until the UV cutoff of water at 200 nm (18,21). It is significant to note that there has been no previous evidence of UV emission from the bubble cavitational collapse due to the fact that photons of energies greater than 6 eV tend to be absorbed by water molecules (11,19). Next, when bubbles sustaining cyclic cavitation collapse due to an ultrasonic field are placed within the near neighborhood of a solid surface, symmetry conditions are disrupted such that the general morphology of cavitation bubble collapse transitions from that of spherically symmetric collapse (Fig.…”

Lasers blow a bigger bubble

“…A better knowledge of bubble-bubble interactions will be the first step towards understanding multi-bubble sonoluminescence (MBSL), the light emission by thousands of bubbles in a bubble cloud under oscillating high pressure. Here, the bubbles disturb one another, so the collapses are much weaker on average, and the spectra of the emitted light have distinct lines 7 , in contrast 6 to those of SBSL -implying that the gas in SBSL is so hot that emission lines are thermally smeared out. Ohl et al 3 have already taken a step towards studying bubble interactions by generating a bubble near a wall.…”