L -B I A Flip-conference.org/previous_editions/LIP2014/abstracts/NR... · 2018-06-20 · wave...
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LASER-BUBBLE INTERACTIONS UNDER THE ACOUSTIC FIELD Honoh SUZUKI * and I-Yin Sandy LEE Department of Chemistry, University of Toyama, 3190 Gofuku Toyama 930-8555 Japan *Corresponding author: [email protected] Abstract Bubbles in the acoustic field have attractive optical properties that are potentially useful in photochemical and biomedical applications. As a step toward realization of such possibilities, translational dynamics of acoustically driven bubbles and the laser-induced cavitation under the acoustic field have been investigated. Computational results on the optical near field of Mie scattering are also discussed in the context of photochemical enhancement. 1 Introduction Bubbles play an essential role in sonochemistry and sonoluminescence. When driven by an external acoustic field, they can expand and shrink in resonance, and generate a hot spot with catalytic activity and light emission [1]. Extensive research has been carried out to elucidate the mechanism of sonoluminescence [2]. Bubbles can also be important in laser-induced processes. During our research on carbon nanotube suspensions in water, we found that short-lived, transient bubbles are generated by laser irradiation, which leads to nonlinear optical scattering, photoacoustic emission, and acoustic resonance of a bubble swarm [3,4]. Such transient cavitation is also crucial in laser-induced rupture of liposomes, in which transient bubbles (with a lifetime of several microseconds) act as a ‘micro-hammer’ to break the liposome membrane and trigger the drug delivery [5]. In these cases, bubbles show promise as photoacoustic and mechanical devices for biomedical applications. Bubbles are generally biocompatible (unless there are too many of them). They have a high refractive index contrast, and are flexible in their size crossing over Fresnel and Fraunhofer regions. Therefore, it is reasonable to envision them also as an optical device for biomedical, photonic, and photochemical applications. Indeed, optics of bubbles is a long and well established field of research, especially in the context of physical optics [6,7]. To explore the possibility for such applications, however, it is mandatory that we sustain and control the position of the bubbles in the ultrasonic field with a high precision, and that we understand the interactions of the acoustically driven bubble with laser pulses. In this paper, we describe our recent results on the translational dynamics of acoustic bubbles, and the laser- induced cavitation under the acoustic field. We also discuss computational results on the optical near field of Mie scattering, with photochemical perspectives in mind. Figure 1 Acoustic bubble trap. 2 Experimental Our set-up (Fig. 1) closely follows that for single-bubble sonoluminescence [8]. A 50-mL flask filled with water is sonicated with a ceramic piezoelectric transducer, and monitored with a shielded piezofilm microphone (Measurement Specialties SDT1-028K). A combination of a digital frequency generator (Strawberry Linux USB-DDS), a home-built preamplifier, a power amplifier, and an LC oscillator is used to drive the transducer. A computer- controlled scan of the frequency, the input voltage, and the inductance determines the optimal condition for trapping a single bubble at the anti-node of the standing acoustic wave (typically around 36 kHz). During each experiment, the phase drift between the driving and monitored signals is compensated by adjusting the frequency in 10 Hz intervals, which has improved the stability of the trapped bubble. The trapped bubble is imaged by using a microscope with a long working distance (79 mm) (Specwell M0616) and a Koehler illuminator. Mie scattering measurements are done with a diode-pumped laser (cw, 532 nm, 40 mW), an optical fiber, and a photomultiplier tube. Laser-induced cavitation is performed with a YAG laser (1064 nm, pulse duration 5 ns, maximum pulse energy 450 mJ). NR-5.1
Transcript of L -B I A Flip-conference.org/previous_editions/LIP2014/abstracts/NR... · 2018-06-20 · wave...
LASER-BUBBLE INTERACTIONS UNDER THE ACOUSTIC FIELD
Honoh SUZUKI* and I-Yin Sandy LEE
Department of Chemistry, University of Toyama, 3190 Gofuku Toyama 930-8555 Japan
*Corresponding author: [email protected]
AbstractBubbles in the acoustic field have attractive optical
properties that are potentially useful in photochemical andbiomedical applications. As a step toward realization ofsuch possibilities, translational dynamics of acousticallydriven bubbles and the laser-induced cavitation under theacoustic field have been investigated. Computationalresults on the optical near field of Mie scattering are alsodiscussed in the context of photochemical enhancement.
1 IntroductionBubbles play an essential role in sonochemistry and
sonoluminescence. When driven by an external acousticfield, they can expand and shrink in resonance, andgenerate a hot spot with catalytic activity and lightemission [1]. Extensive research has been carried out toelucidate the mechanism of sonoluminescence [2].
Bubbles can also be important in laser-inducedprocesses. During our research on carbon nanotubesuspensions in water, we found that short-lived, transientbubbles are generated by laser irradiation, which leads tononlinear optical scattering, photoacoustic emission, andacoustic resonance of a bubble swarm [3,4]. Such transientcavitation is also crucial in laser-induced rupture ofliposomes, in which transient bubbles (with a lifetime ofseveral microseconds) act as a ‘micro-hammer’ to break theliposome membrane and trigger the drug delivery [5]. Inthese cases, bubbles show promise as photoacoustic andmechanical devices for biomedical applications.
Bubbles are generally biocompatible (unless there aretoo many of them). They have a high refractive indexcontrast, and are flexible in their size crossing over Fresneland Fraunhofer regions. Therefore, it is reasonable toenvision them also as an optical device for biomedical,photonic, and photochemical applications. Indeed, opticsof bubbles is a long and well established field of research,especially in the context of physical optics [6,7]. To explorethe possibility for such applications, however, it ismandatory that we sustain and control the position of thebubbles in the ultrasonic field with a high precision, andthat we understand the interactions of the acousticallydriven bubble with laser pulses.
In this paper, we describe our recent results on thetranslational dynamics of acoustic bubbles, and the laser-induced cavitation under the acoustic field. We alsodiscuss computational results on the optical near field ofMie scattering, with photochemical perspectives in mind.
Figure 1 Acoustic bubble trap.
2 ExperimentalOur set-up (Fig. 1) closely follows that for single-bubble
sonoluminescence [8]. A 50-mL flask filled with water issonicated with a ceramic piezoelectric transducer, andmonitored with a shielded piezofilm microphone(Measurement Specialties SDT1-028K). A combination of adigital frequency generator (Strawberry Linux USB-DDS),a home-built preamplifier, a power amplifier, and an LCoscillator is used to drive the transducer. A computer-controlled scan of the frequency, the input voltage, and theinductance determines the optimal condition for trappinga single bubble at the anti-node of the standing acousticwave (typically around 36 kHz). During each experiment,the phase drift between the driving and monitored signalsis compensated by adjusting the frequency in 10 Hzintervals, which has improved the stability of the trappedbubble.
The trapped bubble is imaged by using a microscopewith a long working distance (79 mm) (Specwell M0616)and a Koehler illuminator. Mie scattering measurementsare done with a diode-pumped laser (cw, 532 nm, 40 mW),an optical fiber, and a photomultiplier tube.
Laser-induced cavitation is performed with a YAG laser(1064 nm, pulse duration 5 ns, maximum pulse energy 450mJ).
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LASER-LIGHT AND INTERACTIONS WITH PARTICLES AUGUST 25-29TH, 2014, MARSEILLE, FRANCE
Computation of the Mie near field inside and around abubble, which is illuminated with a plane wave ofmonochromatic light, is done with our program [9].
3 Results and Discussion
3.1 Dynamics and Control of the Translational Motion ofthe Bubble
The trapped bubble can be driven into quasiperiodicand chaotic modes by applying perturbation to theacoustic frequency or pressure. The trajectories arequalitatively classified as circle, helix, eddy, irregular, oval,and flicker. Two hypotheses on the cause for the periodicdancing exist: (i) bubble growth/shrinkage [1], and (ii)nonlinear coupling between translation andhydrodynamics [10]. Our result is consistent with thelatter.
The trapped bubble position can also be controlled (tosome extent) by tuning the acoustic frequency andpressure, with a precision estimated to be less than 80 μm.However, there still exist obstacles against reproducibility,such as acoustic streaming and possible drifts in theconcentration of dissolved gas.
3.2 Laser-Induced Cavitation under the Acoustic FieldIrradiation of a single laser pulse focused at the acoustic
anti-node creates a stable bubble. The threshold in thepulse energy compares well with those for laser-inducedbreakdown (LIB), although LIB without an externalacoustic field generally only leads to transient (short-lived)cavitation [11]. Laser-induced plasma formation is likelyto provide a bubble seed, followed by its growth andstabilization via “rectified diffusion” in the acoustic field[1].
When a second pulse hits the vicinity of the first bubble,a second bubble is created and rapidly fused into the first.The strong attraction between them is interpreted in termsof transient Bjerknes forces (acoustic radiation forces).
3.3 Mie Field CalculationRecently, the optical near field is attracting much
attention with the interest for morphology-dependentresonances (MDR) [12] and photonic jets [13]. To examinethe possibility of photochemical enhancements near thesurface of the bubble, we have computed the near fieldinside and around a bubble (with a diameter of 1 μm) inwater, irradiated with the 1064-nm light (Fig.2). The topand middle figures depict irradiance, which indicatessignificant deformation and enhancement near the bubblesurface. Also, the small size of the bubble allowspenetration of the field into it, which may be analysed interms of evanescent wave and optical tunnelling [6].
Figure 2 Mie field around a 1-μm bubble (the refractive index n= 1) in water (n = 1.3206) irradiated with the plane-wave light of1.064μm. Incident direction = z-axis (from left to right); linearpolarization = x-axis; x-z plane (y = 0) spanning +-1μm isshown. (Top) Surface map of irradiance (I); (middle) 3D mapplotting I as the height (y-axis); and (bottom) surface map ofellipticity of the electric field.
The bottom figure shows ellipticity of the electric vectorfield [14], which clearly indicates that elliptic polarization
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is generated from the incident linear polarization; thus, thebubble acts as a sort of a wave plate or retarder. However,the vibration ellipse is not perpendicular to the Poyntingvector but nearly sitting on the x-z plane, and highlylocalized at the side faces of the bubble. Similar behaviourin ellipticity has been found in the case of other scatterers.Its significance (or insignificance) in relation withphotochemical enhancement is yet unclear to us at themoment. (It is also noted that the strong ellipticity in the‘shadow’ region is misleading and actually insignificant,because there is little irradiance there.)
4 AcknowledgementWe thank M. Takeda, Y. Ina, and H. Maekita for their
experimental support. This work is supported by theJapanese Ministry of Education, Science and Culture(Grant no. 23550010).
5 References[1] T. Leighton, The acoustic bubble (Academic Press, 1994). .
[2] K.S. Suslick, K.S., Flannigan, D.J., Inside a collapsing bubble:sonoluminescence and the conditions during cavitation, Annu. Rev.Phys. Chem. 59: 659-683 (2008).
[3] Lee, I-Y.S., Matsuo, T., Suzuki, H., Photosensitization of nonlinearscattering and photoacoustic emission from single-walled carbonnanotubes, Appl. Phys. Lett. 92: 103122 (2008).
[4] Lee, I-Y.S., Hayama, Y., Suzuki, H., Osawa, T., Photoacousticsensitization and laser-induced cavitation in polymer solutions bycarbon nanotubes, J. Phys. Chem. C 114: 22392-22397 (2010).
[5] Suzuki, H., Lee, I-Y.S., Sakai, T., Laser-Induced Rupture of InfraredDye-Doped Liposomes, Nanomaterials for Biomedicine (Ed. by R.Nagarajan), ACS Publications, Chapter 8, pp 175-189 (2012).
[6] Marston, P.L., Kingsbury, D.L., Scattering by a bubble in waternear the critical angle: interference effects, J. Opt. Soc. Am. 71: 192-196(1981).
[7] Onofri, F.R.A., Radev, S., Sentis, M., Barbosa, S., Physical-opticsapproximation of near-critical-angle scattering by spheroidal bubbles,Optics Letters, 37: 4780-4782 (2012).
[8] Steer, W.A., Sonoluminescence experiment: sound into light,http://www.techmind.org/sl/ (2007).
[9] H. Suzuki, BHFIELD: A Fortran program for the Mie fieldcalculation (Open Source), University of Toyama (2009). [available athttp://www.scattport.org/]
[10] Mettin, R., A.A. Doinikov, Translational instability of a sphericalbubble in a standing ultrasound wave, Applied Acoustics 70: 1330-1339(2009)
[11] Vogel, A., et al., Energy balance of optical breakdown in water atnanosecond to femtosecond time scales, Applied Physics B: Lasers andOptics 68: 271-280 (1999).
[12] Lock, J.A., Excitation efficiency of a morphology-dependentresonance by a focused Gaussian beam, JOSA A 15: 2986-2994 (1998).
[13] Chen, Z., Taflove, A., Backman, V., Photonic nanojet enhancementof backscattering of light by nanoparticles: a potential novel visible-light ultramicroscopy technique, Optics express 12: 1214-1220 (2004).
[14] M. Born, and E. Wolf, Principles of optics: electromagnetic theory ofpropagation, interference and diffraction of light. Cambridge UniversityPress (1999).
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