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Journal ArticleDOI

Cavitation bubble wall pressure measurement by an electromagnetic surface wave enhanced pump-probe configuration

04 Apr 2019-Applied Physics Letters (AIP Publishing LLC AIP Publishing)-Vol. 114, Iss: 13, pp 134101
TL;DR: In this article, a pump-probe setup based on the detection of the light scattered at the surface of a one-dimensional photonic crystal was designed to sustain a surface electromagnetic wave in the visible range and to enhance the optical response.
Abstract: We report on the measurement of the pressure associated with a shock wave within a very thin layer (100 nm) in proximity of a boundary surface. In the experiments, the shock wave was emitted by a cavitation bubble generated by a pulsed pump laser in water. We developed a pump-probe setup based on the detection of the light scattered at the surface of a one-dimensional photonic crystal, which was purposely designed to sustain a surface electromagnetic wave in the visible range and to enhance the optical response. In order to better understand the phenomenon, we implemented numerical simulations to describe the light scattering intensity distributions through a modified Rayleigh's method. We report, with a LoD of ∼ 0.1 MPa, the measurements of the pressure at a surface in the presence of a laser-induced cavitation bubble generated at different distances from the surface and for different pulse energies.

Summary (1 min read)

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Summary

  • The authors developed a pump-probe setup based on the detection of the light scattered at the surface of a one-dimensional photonic crystal, which was purposely designed to sustain a surface electromagnetic wave in the visible range and to enhance the optical response.
  • In order to better understand the phenomenon, the authors implemented numerical simulations to describe the light scattering intensity distributions through a modified Rayleigh’s method.
  • The authors report, with a LoD of ~0.1 MPa, the measurements of the pressure at a surface in presence of a laser-induced cavitation bubble generated at different distances from the surface and for different pulse energies.

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1
Cavitation bubble wall pressure measurement by an electromagnetic
surface wave enhanced pump-probe configuration
Agostino Occhicone
1,*
, Giorgia Sinibaldi
2
, Norbert Danz
3
, Carlo Massimo Casciola
2
, and Francesco Michelotti
1
1
SAPIENZA Università di Roma, Department of Basic and Applied Sciences for Engineering, via A. Scarpa, 16, 00161 Roma, Italy
2
SAPIENZA Università di Roma, Department of Mechanical and Aerospace Engineering, via Eudossiana, 18, 00184 Roma, Italy
3
Fraunhofer Institute for Applied Optics and Precision Engineering, A.-Einstein-Str. 7, 07745 Jena, Germany
* corresponding author: agostino.occhicone@uniroma1.it
ABSTRACT
We report on the measurement of the pressure associated to a shock wave within a very thin layer
(100 nm) in proximity of a boundary surface. In the experiments, the shock wave was emitted by a
cavitation bubble generated by a pulsed pump laser in water. We developed a pump-probe setup based
on the detection of the light scattered at the surface of a one-dimensional photonic crystal, which was
purposely designed to sustain a surface electromagnetic wave in the visible range and to enhance the
optical response. In order to better understand the phenomenon, we implemented numerical simulations
to describe the light scattering intensity distributions through a modified Rayleigh’s method. We report,
with a LoD of ~0.1 MPa, the measurements of the pressure at a surface in presence of a laser-induced
cavitation bubble generated at different distances from the surface and for different pulse energies.

2
In this work, we experimentally demonstrate a new pump-probe pressure sensing scheme exploiting
the peculiar properties of surface electromagnetic waves (SEW) sustained at the interface between a one-
dimensional photonic crystal (1DPC) and water (Bloch surface waves – BSW). We used the technique to
reveal the pressure associated with the shock wave released by a cavitation bubble generated by a laser
pulse in proximity of a boundary surface.
Bubbles’ cavitation is one of the most discussed topics in fluid dynamics. Generally, it is associated with
erosion damage [1], but it is currently reconsidered for a wide range of modern applications within
medicine [2], microfluidics [3] and other fields [4]. Accessing highly resolved pressure measurements at a
boundary surface is of extreme interest to unveil the physical mechanisms governing the modification of
cavitation bubble dynamics in proximity of the surface and could improve practical applications of
cavitation bubbles, such as their interaction with endothelial barriers [5], surfaces’ cleaning [6], and
lithotripsy [2].
Literature is rich of experimental works on bubbles cavitation, in which the phenomenon is imaged by
a fast camera and the associated pressure field is measured by means of a hydrophone, usually based on
either an optical fibre probe (FOPH) [7] [8] [9] or a polyvinylidene piezoelectric film (PVDF). PVDF
hydrophones are commonly used to carry out local pressure measurements at boundary surfaces, with
the main advantage of resolving pressure changes better than the FOPH type. However, measuring the
pressure field by means of such needle hydrophones, which typically have a diameter of 125-600 μm,
involves embedding the needle in the boundary wall, with the sensitive tip at the surface. Under such
conditions, the pressure field at the surface can be perturbed by the discontinuities at the needle tip.
Moreover, mapping the field along the surface requires multiple needles, and more discontinuities would
appear. The optical scheme proposed here permits to measure the pressure field within a 100 nm thick
layer at the surface with a transverse resolution of the order of 200 μm. In the experiments, we generated
shock waves well inside water and detected their pressure upon their interaction with the 1DPC/water
interface.

3
BSW in the visible range [10] have been demonstrated recently to be very attractive and suitable for
non-invasive measurements in proximity of a solid-fluid interface [11] [12]. In the case of BSW, the solid
is a dielectric multi-layered structure characterized by a photonic band gap, in which light propagation
inside the 1DPC is forbidden. The localization of the BSW at the 1DPC/fluid interface is granted by
Bragg and by total internal reflection (TIR), taking place at the 1DPC and the fluid medium sides,
respectively [13]. The BSW field envelope decays exponentially on both sides. BSW can be excited by
means of prism coupling in the Kretschmann-Raether total internal reflection (KR-TIR) configuration
[14].
In our experiments, the nucleation of bubbles was induced by a focused pulsed laser beam (pump) [4]
[15] [16]. The laser was a frequency-doubled Q-switched Nd:YAG-laser (Litron Nano S 35-15), which
delivered laser pulses (LP) at the wavelength λ
pump
=532 nm, with a duration τ=8 ns, as well as tunable
repetition rate and pulse energy up to f=15 Hz and E=30 mJ, respectively.
In order to get a highly symmetric laser-generated plasma [3] [4] [15] [17], the laser beam was first
expanded (Galilean telescope with spherical lenses, focal lengths -25 mm and 200 mm) and then focused
(spherical lens, focal length 75 mm) into a small volume with a relatively large numerical aperture
NA=0.21. Such a NA value reduces heating of water inside the laser beam in the proximity of the focal
point [4].
As shown in FIG. 1(a), the pulsed laser beam reached from top a transparent glass cavitation cuvette,
which was 35 mm deep and 25 mm by 30 mm wide. One lateral facet of the cuvette was constituted by
a 1DPC coated on a microscope slide. A system of mirrors and a micrometric mechanical stage permits
to change the distance of the focusing and the bubble nucleation point from the 1DPC surface. In the
experiments such a distance was about 1 cm.

4
FIG. 1. a) Sketch of the BSW based optical detection set-up. The light source is a He-Ne laser at 632.8 nm. The
light is polarized and focused with a lens, f
1
, on the 1DPC through the KR-TIR configuration. The reflected
light was stopped through a slit (S) and the scattered light collected by a lens, f
2
, that focuses on the photodiode.
b) Video frames acquired for two LP energy levels: 27.0 mJ and 29.1 mJ. The videos were acquired at a frame rate
of 80 kfps.
FIG. 1(b) shows sequences of video frames acquired by means of a fast camera (Photron FastCam mini
UX100 fitted with an objective Nikon Micro-Nikkor 105 mm f/2.8G IF-ED) during the bubble
nucleation experiments with a background illumination, when the pulse energy was either E
1,LP
=27.0 mJ
or E
2,LP
=29.1 mJ. The fast camera was set to the framerate 80 kfps, i.e. one frame every 12.5 μs, and to a
field of view 25.3×1.1 mm
2
. From the first frame of both sets shown, we can see that, despite the large α
value, at both the energy levels the plasma was extended and more than one plasma spot were visible. At
E
1,LP
, the series of frames showed the nucleation of a single bubble that then collapsed with an asymmetric
shape. Increasing the LP energy to E
2,LP
, the effects on the plasma shape was more pronounced and the
bubble lost its symmetry [18]. Two well separated plasma spots were visible, and two bubbles were
formed, which then grew and coalesced, but with final asymmetric shape. The resulting bubble reached
its maximum radius, and, at the collapse, it assumed the shape of an “eight”; at the end of the process,
two residual bubbles were formed.
The 1DPC used in the experiments were deposited on standard glass microscope slides by plasma ion
assisted evaporation (PIAD) under high vacuum conditions by means of an APS904 coating system
(Leybold Optics). The dielectric materials used were SiO
2
(silica), Ta
2
O
5
(tantala) and TiO
2
(titania). The
deposition rates were: 0.5 nm/s for SiO
2
, 0.4 nm/s for Ta
2
O
5
and 0.25 nm/s for the TiO
2
layer [19]. As
shown in FIG. 2(a), the multilayer stack was formed by a repetitive unit with thicknesses d
SiO
2
=275 nm

5
and d
Ta
2
O
5
=120 nm (two period and half) and topped by a two titania and silica thin layers that were both
20 nm thick. The refractive indices of the layers at λ
probe
=632.8 nm are: (TiO
2
) 2.293+
+i1.83×10
-3
, (SiO
2
) 1.447+i5×10
-6
, (Ta
2
O
5
) 2.075+i5×10
-5
.
As shown in FIG. 1(a), the back face of a 1DPC coated slide was coupled to a BK7 glass prism by
means of an optical contact oil. The free surface of the 1DPC is used as a side facet of the transparent
cavitation cuvette, allowing to keep the 1DPC in contact with water, where the bubbles and pressure
waves are generated.
FIG. 1(a) shows the optical configuration used to excite the probe BSW. The beam emitted by a CW
He-Ne laser at λ
probe
=632.8 nm is linearly polarized along the σ direction and is focused onto the 1DPC
by means of a spherical lens (f
1
=150 mm) through the BK7 coupling prism in the KR-TIR configuration
and sensing local refractive index changes. A θ-2θ rotation stage allows to set the probe beam incidence
angle θ
i
and the detection angle θ
d
. When
i
=
BSW
, a BSW is resonantly excited at the interface between
the 1DPC and water. For the present 1DPC design, the penetration depth of the BSW exponential tail
in water is ξ ~ 100 nm and the BSW propagates along the surface for coupling distance δ~200 μm before
being out-coupled in the prism [20]. Such a condition permits to sense pressure changes in a water volume
with extension δ·ξ·η, where η is the focal spot size that is in order of few tens of micrometers.
With reference to FIG. 2(a), the reflected beam is constituted by two components: the specularly
reflected beam at θ
r
and a m-line at θ
s
due to scattering of the BSW (see Eqs. II.1 and II.2, respectively,
in the supplementary material). The specularly reflected light is filtered out by a beam stop, whereas the
m-line is transmitted by a slit (S) and collected by a second spherical lens (f
2
= 50 mm) that focuses onto
a photodetector. The slit provides an angular resolution of ~0.09°. The voltage signal V
p
at the
photodetector was acquired with an oscilloscope (Tektronix 2440) that was controlled by a PC through
a LabView VI.
In FIG. 2(b) and (c), we show the results of the numerical calculations obtained for the two reflected
components and carried out by means of a modified Rayleigh’s method, which was already applied to
BSW and discussed in Ref. [21] and [22] (details in the supplementary material). As sketched in FIG. 2(a),

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References
More filters
Book
03 May 1988
TL;DR: In this article, surface plasmons on smooth surfaces were used for light scattering at rough surfaces without an ATR device, and surface plasmon on gratings for enhanced roughness.
Abstract: Surface plasmons on smooth surfaces.- Surface plasmons on surfaces of small roughness.- Surfaces of enhanced roughness.- Light scattering at rough surfaces without an ATR device.- Surface plasmons on gratings.- Conclusions.

4,890 citations


"Cavitation bubble wall pressure mea..." refers methods in this paper

  • ...BSW can be excited by means of prism coupling in the Kretschmann-Raether total internal reflection (KR-TIR) configuration [14]....

    [...]

Journal ArticleDOI
TL;DR: In this article, a diagonalization of the unit cell translation operator is used to obtain exact solutions for the Bloch waves, the dispersion relations, and the band structure of the medium.
Abstract: The propagation of electromagnetic radiation in periodically stratified media is considered. Media of finite, semi-infinite, and infinite extent are treated. A diagonalization of the unit cell translation operator is used to obtain exact solutions for the Bloch waves, the dispersion relations, and the band structure of the medium. Some new phenomena with applications to integrated optics and laser technology are presented.

1,446 citations


"Cavitation bubble wall pressure mea..." refers background in this paper

  • ...3 BSW in the visible range [10] have been demonstrated recently to be very attractive and suitable for non-invasive measurements in proximity of a solid-fluid interface [11] [12]....

    [...]

Journal ArticleDOI
TL;DR: In this article, the authors investigated the partition of laser energy between these channels during breakdown in water, and found that the absorption at the breakdown site first decreases strongly with decreasing pulse duration, but increases again for < 3p s.
Abstract: During optical breakdown, the energy delivered to the sample is either transmitted, reflected, scattered, or ab- sorbed. Pathways for the division of the absorbed energy are the evaporation of the focal volume, the plasma radiation, and the mechanical effects such as shock wave emission and cav- itation. The partition of laser energy between these channels during breakdown in water was investigated for four selected laser parameters typical for intraocular microsurgery ( 6-ns pulses of 1 and 10 mJ focused at an angle of 22 ,a nd30-ps pulses of 50 mJ and 1m Jfocused at 14 ,a ll at1064 nm). Scattering and reflection were found to be small compared to transmission and absorption during optical breakdown. The ratio of the shock wave energy and cavitation bubble energy was approximately constant (between 1.5:1 and 2:1). These results allowed us to perform a more comprehensive study of the influence of pulse duration ( 100 fs- 76 ns )a nd focus- ing angle (4- 32) on the energy partition by measuring only the plasma transmission and the cavitation bubble energy. The bubble energy was used as an indicator for the total amount of mechanical energy. We found that the absorption at the breakdown site first decreases strongly with decreasing pulse duration, but increases again for < 3p s. The conversion of the absorbed energy into mechanical energy is 90% with ns pulses at large focusing angles. It decreases both with de- creasing focusing angle and pulse duration (to < 15 %f or fs pulses). The disruptive character of plasma-mediated laser effects is therefore strongly reduced when ultrashort laser pulses are used.

473 citations

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate experimentally with microparticle tracking velocimetry that the strongest forcing of particles occurs during a very brief time interval of the bubble oscillation period, during which a jet flow impacts and spreads radially along the surface, thus transporting the particles with it.
Abstract: When bubbles expand and collapse close to boundaries, a shear flow is generated which is able to remove particles from the surface, thus locally cleaning it. Here the authors demonstrate experimentally with microparticle tracking velocimetry that the strongest forcing of particles occurs during a very brief time interval of the bubble oscillation period. During this interval a jet flow impacts and spreads radially along the surface, thus transporting the particles with it.

279 citations


"Cavitation bubble wall pressure mea..." refers background in this paper

  • ...Accessing highly resolved pressure measurements at a boundary surface is of extreme interest to unveil the physical mechanisms governing the modification of cavitation bubble dynamics in proximity of the surface and could improve practical applications of cavitation bubbles, such as their interaction with endothelial barriers [5], surfaces’ cleaning [6], and lithotripsy [2]....

    [...]

Journal ArticleDOI
TL;DR: In this paper, a new fiberoptic probe hydrophone overcomes most of the problems involved with the use of piezoelectric hydrophone technology in non-linear ultrasonic and shock-wave fields.

253 citations


"Cavitation bubble wall pressure mea..." refers background in this paper

  • ...In the inset, we show the pressure measured by a classical FOPH when the pressure shock waves are collected for different laser pulse energies. c) BdSw temporal position vs bubble nucleation position. d) BdSw pressure peak value versus the pulsed laser energy....

    [...]

  • ...PVDF hydrophones are commonly used to carry out local pressure measurements at boundary surfaces, with the main advantage of resolving pressure changes better than the FOPH type....

    [...]

  • ...The latter is in contrast with the results reported in literature [15] [28] and with what we observed with a FOPH (inset of FIG....

    [...]

  • ...We evaluated the LoD as one standard deviation of the measurement noise in a 10 μs window for the following cases: 1. single cavitation event, LoD1=5 MPa; 2. average of 128 events, LoD128=0.3 MPa; 3. average of 128 events and SG filtering as described above, LoDSG-f=0.1 MPa The LoD1 value should be compared to the LoD of commercial FOPH (around 0.5 MPa, 100 MHz bandwidth) [26], which make use of dedicated electronics for signal conditioning that were not used in our case and that could improve the LoD1 value....

    [...]

  • ...Literature is rich of experimental works on bubbles’ cavitation, in which the phenomenon is imaged by a fast camera and the associated pressure field is measured by means of a hydrophone, usually based on either an optical fibre probe (FOPH) [7] [8] [9] or a polyvinylidene piezoelectric film (PVDF)....

    [...]

Frequently Asked Questions (1)
Q1. What are the contributions mentioned in the paper "Cavitation bubble wall pressure measurement by an electromagnetic surface wave enhanced pump-probe configuration" ?

The authors report on the measurement of the pressure associated to a shock wave within a very thin layer ( 100 nm ) in proximity of a boundary surface. In order to better understand the phenomenon, the authors implemented numerical simulations to describe the light scattering intensity distributions through a modified Rayleigh ’ s method. The authors report, with a LoD of ~0.