Magic bubbles Ivan Lomachenkov

Introduction Put a small gas bubble into a 100 ml flask, filled with water, expose the water to sound and the gas bubble will radiate visible light if proper conditions are applied. This phenomenon, called the Single-Bubble Sonoluminescence (SBSL) is an amazing process. It converts the energy of sound into energy of light. This phenomenon was observed for the first time by L.A.Crum and D.F.Gaitan about ten years ago (USA, University of Mississippi). To foto setup 16-4-2019 Ivan Lomachenkov-HST2001

What is going on? When the bubble is trapped by the sound field (that is produced by a sine-generator) it is carried into the centre of the flask. There its size begins to change. When the sound pressure drops, the size of bubble expands to about 50 microns. To foto setup 16-4-2019 Ivan Lomachenkov-HST2001

Then the sound pressure is increased and pressure difference between the inside and outside leads to a catastrophic collapse. The bubble size decreases from its 50-micron maximum radius to a size of about O.5 microns. Really the bubble suddenly slams and just in this moment the flash is produced. According to the measurements by B.Barber (member of group by S.Putterman, USA, University of California), the flashes are extremely short – about 50 picoseconds. To foto setup 16-4-2019 Ivan Lomachenkov-HST2001

Practical setup of the experiment The energy of the electrical vibrations is transformed into energy of the sound field by piezoceramic transducers, that are glued on the surface of the flask. The electrical parts of the experiment consist of coil inductance and transducers. The capacitance of the transducers is about 20 nF. As the flask with water is a resonance system, mechanical and electrical parts of the facility must resonate. In our experiments the resonance frequency was about 27 kHz. To foto setup 16-4-2019 Ivan Lomachenkov-HST2001

The voltage on the piezo transducers and coil may be many times greater than the amplifier output voltage, as the circuit is reactive. To foto setup 16-4-2019 Ivan Lomachenkov-HST2001

Theoretical problems The SBSL attracts much attention nowadays because there isn’t a real physical model for this phenomenon. We can say that now we have more questions than answers: In what condition is the gas inside the bubble at the moment of the slams? What is the real temperature of the gas? How to find a method to measure the temperature inside? 16-4-2019 Ivan Lomachenkov-HST2001

These and others questions are in need of answers What is the reason of the amazing stability of the flashes (like the stability of the laser’s flashes)? It is known that the light is mostly ultraviolet. Since the water absorbs all radiation with wavelength less then 200 nm, there’s the question: what’s the smallest wavelength of the radiation? These and others questions are in need of answers 16-4-2019 Ivan Lomachenkov-HST2001

Thanks This experiment has been realized with the help of my colleagues M.Miller and A.Sermygin (Russia, Moscow region, Dubna, Institute in Physical-Technical Problems). I thank them all. I also thank my student D.Podgrudkov for preparing the computer animation. Our group (I.L., M.M., A.S.) is planning to continue the experiments at the University Centre of Joint Institute for Nuclear Research. 16-4-2019 Ivan Lomachenkov-HST2001

The experiment 16-4-2019 Ivan Lomachenkov-HST2001