|
|
Sonoluminescence
Single Bubble
Sonoluminescence (SBSL) is the emission of flashes of light by imploding air
bubbles in liquid. It was first observed as random flashes of light during
studies of cavitation. Recently, repetitive emission of SL has been produced
under relatively stable, reproducible experimental conditions. The excellent
stability of SL from single acoustically levitated bubbles has made possible
detailed studies of the emission characteristics[2]. However, since each
flash emits only about one million photons, these measurements have
generally required averaging the characteristics over a large number of
flashes.
|
|

Fig6 - apparatus for single
bubble sonoluminescence. The ultrasound is applied across the rounded bottom
flask and hence bubble is created. |
Other applications
Sonoluminescence
Sonofusion
Chemoluminescence
Sonocrystalisation
Polymer and Biro- materials |
Sonocatalyst |
|
In single bubble
sonoluminescence, the bubble is concentrating the energy of the acoustic
vibrations be a factor of one trillion. The flashes are so brief that to
measure the properties of light , we must use photodetectors that respond
more quickly than those employed by high-energy physicists. And this is the
only means of generating picosecond flashes of light that does not require
expensive lasers, which might lead to development of nuclear fusion due to
its achievement in focusing of energy.
|
|
|
|
Fig7 - blast of light from single
bubble luminescence |
|
This phenomena is
not new, in 1920s and 1930s, chemists working with loudspeakers
developed for sonar systems during world war I came across that a strong
sound field could catalyze reactions that take place in an aqueous solution.
A German scientist, Reinhard Mecke of the University of Heidelberg, stated
that the amount of energy needed for a chemical reaction is the same as that
needed to excite the emission of light from an atom. So he suggested a
search such a signal. Soon afterward, in 1934, H. Frenzel and H.Schultes of
the University of Cologne discovered sonoluminescence in a bath of water
excited by acoustic waves.[1]. In 1990, Gaitan and Crum showed that a single
air bubble can levitate in a
standing acoustiv wave
setup in sufficiently degassed water until light is emitted when acoustic
stress is increased and this is called single bubble sonoluminescene(SBSL),
which bring attention to many researchers across the world[15].
|
|
|
|
|
The mechanisms that
convert sound into light still remain unexplained despite many various
theoretical approaches. A gas bubble is created into a flask filled with
fluid. For example degassed, purified water and air are an excellent pair
for the phenomenon. A coherent beam of ultrasound makes the bubble cavitate,
i.e. to expand and compress in phase with the sound wave. Typical frequency
for the sound wave is 25 kHz.[3] and flashes, which comprise over 105
photons, is genrated and has energy of about 3eV. Furthermore, these burst
can occur in a continuously repeating ad has greater [pwer than 1.0 mW
within duration of less han 100ps, which is about 100 times faster compared
to the fastest visible transition (3 --> 2) in the hydrogen atom.[6]. Also
the amount of light emitted with each flash is related to the temperature
drops, and this is known as bubble temperature sensitivity.[5] [1] |
|
|
The apparatus can be
easily set up using piezo electric transducer – used in alternating fields
of compression and compression-on the top a cylindral flask filled with
water. Submerged in the water is a small piece of toaster wire, which boil
the water and cause a bubble filled with water vapor forms. Before the vapor
recondensed, air dissolved in the water flows into the pocket to create an
air bubble. This bubble is then trapped at the centre of the cylindral flask
annd monitored its motion using laser[18]. However many more set ups have
been developed during a few year and more complicated apparatus are
used. |
|
|

Fig8 - show the set up of apparatus
for single bubble sonoluminescence |
|
|
Although the
mechanism of single bubble sonoluminescense is difficult to explain, the
sensvity to temperature suggested that we could learn more about it. One
interesting idea is replacing the air bubble with other gas such as nitrogen
, noble gas etc.. Surprisingly the pure nitrogen and pure oxygen[16] gas
hardly produced any light. By increasing noble gas content of a bubble can
dramatically stabilizes the bubble motion and increases the light
emission[8][14] |
|
|
The most rational picture of sonoluminescence involves the creation of a
"cold" dense plasma by an imploding shock wave, neither the imploding shock
nor the plasma has been directly observed[17]. However, in 1995 Lepoint
shows that single argon bubble oscillating nonlinearly in an acoustic field
give plasma developed inside the argon bubble and is assumed to be in local
thermodynamic equilibrium[8][12] and this might lead to application such as
nuclear fusion(sonofusion). |
|
|
The conditions within the bubble during the last stages of the nearly
catastrophic implosion are thought to parallel the efforts aimed at
developing inertial confinement fusion. A limited review on the topic of SL
and its possible connection to bubble nuclear fusion is presented here. The
emphasis is on looking for a link between the various forms of SL observed
and the severity of bubble collapse or implosion. A simple energy analysis
is also presented to enable the search for an appropriate parameter space
and an experimental technique for achieving energy densities required for
triggering fusion reactions within the bubble.[13] |
|
|
Sonoluminescence is not only achived in gas bubbles. Some solutions and
compounds, forexample solutions of sulfuric acid and sulfur dioxide enhances
give the SL spectra which its intensity decrease with an increase in
concentration of the solution, Excited SO2 molecules formed in
sulfuric acid due to sonolysis are luminescence emitters. The proposed
mechanism of bright SL in these systems is based on the energy transfer from
the electron-excited sonolysis products to the SO2 molecules in cavitation
bubbles.[9]. In salts (TbCl3, Tb(NO3)(3), PrCl3, EuCl3, CeCl3, and DyCl3),
the SL spectrum and intensity of multi-bubble sonoluminescence (SL) of water
was observed at a frequency of 20 kHz[10]. Furthermore some organic
compounds or polymer were also discovered. [11] |
|
|
Sonoluminescense also happen in many bubbles system, which response to high
frequency and be far more complicated[12]. However, the future is clear
about application and popularity among scientist with more publications
nowadays and surely this nature’s most nonlinear system might become a
source of light in our daily light one day. |
|
 |
|
|
|
|
Fig9 -
Sonoluminescence from a high intensity
ultrasonic horn |