Sonoluminescence

 

This is an excerpt of what I think was my very first website on the old geocity, setup in 1998, but – most importantly – this is the story of four students that had fun with an amazing phenomenon, sonoluminescence.

Welcome

We were four students: Alessandro Esposito, Luca Pellegrino, Claudio Demelia and Alessandro Torrielli. We designed, built and characterized an acoustic resonator to perform experiments on sonoluminescence. That was a great experience and, I believe, it was a wonderful experiment for 4 undergraduate students. That was our first “real” experiment. I believe that all of us may agree on the fact that was an incredible experience.

After months of construction and tests, we disassembled all the system from the electronic lab to the optics one. Ready to go. Dark room, hands on the power and frequency controllers. After a while, we jumped on our chairs. Yes, it was the first spark! The excitement lasted a few seconds just to become pure astonishment. By tuning the frequency of the acoustic field, we got a wonderful standing wave. The resonator simply shone. Thousands of air bubbles positioned themselves onto a periodic lattice generating a dim and diffuse blue light that for us was brighter than a thousands suns.

I will always remember the excitement and the many people that visited from the Department of Physics and elsewhere just to see this extraordinary phenomenon.

What is sonoluminescence?

To cite wikipedia for once, “Sonoluminescence is the emission of short bursts of light from imploding bubbles in a liquid when excited by sound”. For some time, this was considered a possible mechanism of cold fusion and sonoluminescence was also a subject of a movie “Chain Reaction” with Keanu Reeves and Morgan Freeman. Science can be entertaining, in the lab and at the cinema.

The first images (1997)

We shot some photographs using a 3200ASA film and long exposure (15-30min). Unfortunately, this first run of photographs shots in 1997 suffered from a few issues and we had to shoot new images later in 1998 after further insulating any possible source of stray light. Here some examples.

cil12
This is one of the images we shot in 1997. The red light is stray light from an LED display present in the room that leaked in the dark box we set up.

  

cil24
This is the same shot, digitally cleaned. What you see here is an imperfect standing wave, creating a cylindrically symmetrical 3D lattice of peaks a valleys where bubbles position themselves. Under the action of the acoustic field, bubbles expands and then get compressed therefore imploding. Shockwaves further heats up the gases and induce emission of light. You see lines rather than a lattice of spots because of the long exposure of imaging and blurring caused by movements.

 

 

The 1998 shots

belleanimgif
This is an animation created by several images we collected in 1998, after we improved the dark room. The differences from frame to frame are caused by changes in the frequency of the acoustic field. Below, you will find a number of images collected during this 1998 photo shoot section.

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The report

This is the final report (in Italian only) Sonoluminescence_Report_ITA

The setup

laserprosp
This is the initial plan for the construction of the resonator. The system would include also a laser to detect cavitation within the resonator used to determine resonance frequencies and characterize glass cylinders of various length.

 

labhe
After we built all the electronics and the resonator in the teaching labs, we moved the system to Prof. Siri’s laboratory to use some spare equipment. You may notice the laser (on the right) few lenses and the detector (on the left). Recordings of cavitation were taken or an old paper recorder.
track8
This is a typical track showing resonance peaks
illum
Just an image of the resonator. You may see the top metal plates with the screws holding in place the glass cylinders. On the top of the plates, we bonded the high power ultrasound transducers (not visible) and the metal plates were equipped with o-rings to establish a water tight seal. Small apertures provided the ports we used for filling the system with distilled water and to probe the water temperature. Bubbles are generated by cavitation.

 

 

labott2
This is the optics teaching lab where you see the resonator within a ‘light tight’ enclosure (open in the picture), the camera, the oscilloscope and the frequency generator we used for the experiments.

A visit to an old friend

HPIM3617lit
I believe this is 2009, a fast visit in Genoa to meet Luca (in the foreground). The setup was still operational and used for a Bachelor degree experiment. Here you can see the amplifier (the black box with electronics) and the resonator.

 

 

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