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Highspeed photography of laserinduced breakdown in liquidsW. Lauterborn
Citation: Applied Physics Letters 21, 27 (1972); doi: 10.1063/1.1654204 View online: http://dx.doi.org/10.1063/1.1654204 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/21/1?ver=pdfcov Published by the AIP Publishing Articles you may be interested in HIGHSPEED PHOTOGRAPHY OF DETONATION PROPAGATION IN DYNAMICALLYPRECOMPRESSED LIQUID EXPLOSIVES AIP Conf. Proc. 955, 857 (2007); 10.1063/1.2833261 High-speed scanning laser-induced breakdown spectroscopy at 1000 Hz with single pulse evaluation forthe detection of inclusions in steel J. Laser Appl. 17, 183 (2005); 10.2351/1.1961738 Highspeed holography of laserinduced breakdown in liquids Appl. Phys. Lett. 31, 663 (1977); 10.1063/1.89495 SUBNANOSECOND SCHLIEREN PHOTOGRAPHY OF LASERINDUCED GAS BREAKDOWN Appl. Phys. Lett. 12, 148 (1968); 10.1063/1.1651931 HighSpeed Photography Phys. Today 9, 32 (1956); 10.1063/1.3059894
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rf AUGMENTATION IN CO 2 CONVECTION LASERS 27
1.0r--------------~
... z !!:! v ..: ...
0.8r-
0,," vv 0.6
z;::. ~~ ~v .... '" 0.4 «'" zo.. ~ ;;;
0.2 .... .... «
"" 0 0
o 0
• I I I 2 4 6 8
ElECTRIC AL POWER, D.C. + 0.6 R.F. -KILOWATTS
10
FIG. 4. Variation of the small-signal gain coefficient as a nmction of the dc power level plus 0.6 of the rf auxiliary power for the data of Fig. 3.
in turn, minimizes the local buildup of species which may be deleterious to the stability of the discharge. In support of this possible role of the radio frequency is the improved discharge behavior obtained by the introduction of additional cathode elements more uniformly distributed over the cross section of the discharge channel (compare Figs. 1 and 2). Another explanation9
concerns the rotation of the current density vector resulting in the time-average suppression of instabilities. For certain types of instabilities, the envelope for unstable wave growth lies in a region centered about, or perpendicular to, the current density vector. Waves outside the envelope are damped at a rate faster than the growth rate of the unstable waves within the envelope. By rotating the total current density vector, waves initially within the instability envelope are displaced
from the envelope and are damped out. For such to be the case, the rf frequency must be greater than the growth rate of the unstable wave. In this regard, it is noted that when rf auxiliary power was aligned with the dc field by capacitively coupling through the dc electrodes, no enhancement was found, a result which would be expected from the above viewpoint. The latter experiment was inconclusive, however, in differentiating between the two explanations, in that the uniformity of the discharge was not visually improved.
In summary, it has been demonstrated that application of rf auxiliary power, capacitively coupled into the discharge zone transverse to the dc field, is an effective means of enhancing closed-cycle discharge stability in CO2 lasers, enabling stable operation at high power levels.
The authors wish to acknowledge valuable technical discussions with A. E. Mensing and R. A. Haas and the technical assistance of A. Parasco.
*Research supported in part by the Naval Ordnance Laboratory and the Naval Ordnance Systems Command under Contract No. N60921-70-C-0219.
iC.O. Brown, Bull. Am. Phys. Soc. 16,215 (1971). 2W.L. Nighan, Phys. Rev. A 2, 1989 (1970). 3 A. E. Hill, Appl. Phys. Letters 18, 194 (1971). 4A. C. Eckbreth and J. W. DaviS, Appl. Phys. Letters 19, 101 (1971).
5J . Freudenthal, IEEE J. Quantum Electron. QE-6, 507 (1970), and the references contained therein.
6W.J. Wiegand, Bull. Am. Phys. Soc. 17, 398 (1972). 7p. Bletzinger, M. Hughes, P.D. Tannen, and A. Garscadden in Ref. 6.
BW. P. Allis, S. C. Brown, and E. Everhart, Phys. Rev. 84, 519 (1951).
9R.A. Haas and G. Guckel, Bull. Am. Phys. Soc. 16, 1283 (1971).
High-speed photography of laser-induced breakdown in liquids
W. Lauterborn Drittes Physikalisches Institut der Universitijt Gottingen, 34 Gottingen, Biirgerstrasse 42/44, Germany
(Received 5 January 1972)
A giant pulse of a ruby laser is focused into water, silicone oils, and some other liquids. High-speed photography of the focal region with picture repetition rates up to 850000 pps shows the dynamics of the produced bubbles. These are extremely well suited to study cavitation bubble dynamics. Spherical almost empty bubbles can be produced in water, realizing the Rayleigh bubble model. The shock wave produced by the laser-induced breakdown is made visible by small bubbles suspended in the vicinity. From the radial motion of these bubbles, conclusions can be drawn on the strength of the shock wave.
When intense laser light is focused into a liquid, a number of marked phenomena are observed, among which the occurrence of bubble formation and cavitation has earlier been stated. 1_3 In subsequent investigations, however, the cavitational aspect of laser -induced breakdown has been disregarded almost completely, and emphasis has been given to the generation of shock waves. 4-9 The present investigation employs high-speed photography using picture repetition rates of up to
850000 pps to show cavity formation, growth, collapse, and the rebounds. Early results have already been reported. 10 To save space, only cavity formation is shown in this letter.
The experimental setup is shown in Fig. 1. A ruby laser was used, being Q switched by a Kerr cell. The maximum output energy was in the region of 1 J, the pulse duration being in the range of 30-50 nsec. Lenses
Appl. Phys. Lett., Vol. 21, No. I, I July 1972 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
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28 W. LAUTERBORN
------l I I I I I
* FLASH LAMP
___ ---'"G_RO-'-U;:.;N.;;::D GLASS PLATE
SCALE
I LIQUID I L._,---O ROTATING
START DRUM OR MIRROR CAMERA
FIG. 1. Block diagram of experimental setup.
of different focal lengths were used, as the number and shape of the cavities depend on its value. Liquids used were demineralized, air-saturated, or slightly degassed water, silicone oils, and some other liquids. Both a rotating-drum camera and a rotating-mirror camera were used.
The s~quence of pictures in Fig. 2 taken from a film of 80 frames shows cavity formation by laser-induced breakdown in water under atmospheric pressure and the compression of small bubbles in the vicinity of the breakdown by the shock wave thereby produced. A lens with a focal length of 1. 28 cm in air was used just outside a cuvette (5 X 5x 5 cm) to focus the laser light into the water. An evaluation of the radius-time dependence of a small bubble compressed by the shock wave is given in Fig. 3 together with computed curves (from Ref. 11) resulting from a pressure pulse of sinusoidal shape and 30-nsec duration with pressure amplitudes of Pa=1800, 1500, and 1200 bar. The value of 30 nsec was adopted because of the duration of the laser pulse. The real duration of the pressure pulse is not known, but an estimation of its value can be made. Carome et al. 6 have shown that the duration of the pressure pulse will be less than 200 nsec. This value can therefore be chosen as an upper bound. As strongly collapsing bubbles emit shock waves of duration less than 10 nsec 12
and the generation of bubbles by laser light can be said to be the inverse process, the value of 10 nsee will possibly be closer to the real value and is taken as a kind of lower bound. As for pressure pulses of duration less than 500 nsec the calculated pressure amplitude is inversely proportional to the duration, the value of the peak pressure in the shock wave at the location of the bubble 6 mm distant from the point of breakdown is estimated to be between 225 and 4500 bar. The lower value agrees well with the data of Carome et al. ,6 but the real value may even be more than 4500 bar.
n has already been pointed out that laser-induced bubbles can be used to study cavitation bubble dynamics. 10
To compare bubble motion with existing theory, the generation of spherical bubbles is necessary. This can be achieved by a suitable setup of the experiments. To obtain spherical bubbles, there need not be only one breakdown in the liquid (Fig. 4).
A vast number of films have already been produced.
Appl. Phys. Lett., Vol. 21, No.1, 1 July 1972
.-
FIG. 2. High-speed (853000 pps) photography of bubble formation due to laser-induced breakdown in water and of the compression of small air bubbles by the shock wave produced; the time interval between successive frames is 1.17 p.sec; spacing of the bars to the right of each frame is 1 mm.
Among other results on collapse dynamics, suicide mechanics of the bubbles, and nonlinear bubble oscillations, it was shown that laser-induced spherical bubbles realize the Rayleigh empty-bubble modell3 in water. These results will be published in a series of papers.
300
11m
11\ 200 :::> '0 0 ...
i 100
0 0 2 4 6 (l.17I15eC) 10 - time
FIG. 3. Radius-time curve of a small air bubble compressed by the shock wave of Fig. 2. 0 and x symbolize the splitting of the value for the radius due to a deformation of the bubble by the shock wave.
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HIGH -SPEED PHOTOGRAPHY OF BREAKDOWN IN LIQUIDS 29
I j\
"; CO 0 1-;' " "
a:, J~.
t • 0 'c
0
0 0
FIG. 4. High-speed (547000 pps) photography of bubble formation in silicone oil (static viscosity, 121. 3 P), leading to a spherical bubble; the time interval between successive frames is 1. 83 IJ.sec; the spacing of the bars to the right of each frame is 1 mm.
For better visualization of the different kinds of events observed on laser-generated cavitation bubbles, motion picture films are presently being produced from the frames of the films taken.
The present investigation was sponsored by the Fraunhofer-Gesellschaft and the Deutsche Forschungsgemeinschaft. Thanks are due to G. Fahlbusch of the Institut fUr den Wissenschaftlichen Film, who assisted in taking films with the rotating-mirror camera.
lG. A. Askar'yan, A. M. Prokhorov, G. F. Chanturiya, and G.P. Shipulo, Sov. Phys. JETP 17, 1463 (1963).
2R. G. Brewer and K. E. Rieckhoff, Phys. Rev. Letters 13, 334a (1964).
3R.C. Stamberg and D.E. Gillespie, J. Appl. Phys. 37, 459 (1966).
4C. E. Bell and J. A. Landt, Appl. Phys. Letters 10, 46 (1967). 5E.F. Carome, E.M. Carreira, and C.J. Prochaska, Appl. Phys. Letters 11, 64 (1967).
6E.F. Carome, C.E. Moeller, andN.A. Clark, J. Acoust. Soc. Am. 40,1462(1966).
7J.F. Roach, W. Zagieboylo, andJ.M. Davies, Proc. IEEE 57, 1693 (1969).
8G. Singurel, Rev. Roumaine Phys. 14, 377 (1969). 9M.P. Felix andA.T. Ellis, Appl. Phys. Letters 19,484 (1971).
lOW. Lauterborn, International Union of Theoretical and Applied Mechanics Symposium, Leningrad, USSR, 1971 (unpublished) .
liB.E. Noltingk and E.A. Neppiras, Proc. Phys. Soc. (London) B 63, 674 (1950).
l2U. Radek (private communication). l3Lord Rayleigh, Phil Mag. Ser. 634, 94 (1917).
X-ray diffraction study of single crystals undergoing shock-wave compression*
Quintin Johnson, Arthur C. Mitchell, and L. Evans Lawrence Livermore Laboratory, University of California, Livermore, California 94550
(Received 23 March 1972)
Single crystals of LiF, AI, and graphite have been studied by x-ray diffraction while undergoing shock-wave compression to about 300 kbar. These studies show that single crystals can transform to the hydrostatically compressed state essentially as single crystals, and crystal orientation is preserved.
Earlier work demonstrated that it is possible to conduct an x-ray diffraction experiment during the very short time periods involved in shock-wave compression of materials .1,2 The length of time a typical shock-compressed material is available for viewing can be as short as a few nanoseconds depending upon the wavelength of radiation and the density of material chosen. Using this technique it is possible to investigate some of the more fundamental questions concerning the process of shock-wave compression. One such question concerns the problem of how a single crystal responds to a shock-wave impulse.
While it may not be possible to use x-ray diffraction to inspect the actual shock front because of its vanishingly small thickness, it is possible to observe what has happened crystallographically to the material just behind the shock front. In previous experiments we have shown that a powder sample of LiF shock compressed to about 200 kbar is transformed to a state that is ordered and hydrostatically compressed. 2 Those experiments cannot tell us, however, if an individual crystallite transformed essentially intact or whether there was a disordered period followed by recrystalli-
zation in which the integrity of individual crystallites was not maintained. Recovery experiments, although strongly suggesting the former mode, 3-5 provide only circumstantial evidence since it is extremely difficult to separate out the effects of compression from those of release.
Therefore to provide a first look at the crystallography of a Single crystal just behind the shock front, we have subjected a [100]-oriented crystal of LiF to a shock pressure amounting to about 300 kbar. The apparatus was Similar to that described in Refs. 1 and 2 except that LX04 was used in place of TNT. The results of this experiment are shown on the top record in Fig. 1. Visible in this record are the normal 200 reflections attributable to the Ka line (A = 1. 3922 A) and the K" line (X=1.54178 A). The third line on the right-hand side of the record is the 200 K" line from LiF under shockwave compreSSion. As noted earlier, the compression is that expected for hydrostatic compression with vivo =0. 79 ±0.01, or, in other words, the measured 28 shift indicates a cell constant of 3.72 A which should be compared to the uncompressed value of 4.027 A. The Ka reflection from the shock-compressed state is
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