Experiments show that Sound can be Produced from Light

Experiments show that Sound can be Produced from Light

A researching team at Washington University has figured out a way to use light waves for generating an acoustic wave.

Science has unveiled a lot of secrets about the universe following massive advancements in technology and research. Numerous ideas that were considered fictional in the past are a part of our lives these days. These discoveries reflect the determination of humans to explore as much as possible. Another addition to this incredible list of scientific achievements took place recently when an international team of researchers succeeded in developing a lasing system which can convert light into sound waves. Scientists from the United States, Austria, China, and Japan joined forces to come up with amazing invention.

They used a photon-producing lasing system and converted it into a tunable system that can generate small amounts of ‘Phonons’, which are the end-products of a vibration or an oscillation. This is a first-of-its-kind experiment because this research has broadened the ‘Laser Linewidth’ in phonon laser. Linewidth is used to measure the unwanted noise in the laser and shows the physical integrity of the lasing signal. Similarly, it will take the technology of phonon laser through ‘Exceptional Point’, which is a physical system. Lan Yang, the Edwin H. & Florence G. Skinner Professor of Electrical & Systems Engineering in the School of Engineering and Applied Science, described their work by saying,

We’ve shown that you can use a light field to trigger the mechanical movement that will generate an acoustic (sound) wave. Think of phonon lasing as a counterpart to traditional optic, or photon lasing, with exciting applications in medical surgery, materials science and communications. We have demonstrated a controllable phonon laser that can be tuned for threshold and linewidth, among other potential parameters. Our study for the first time provides direct evidence that exceptional point-enhanced optical noises can be transferred directly to mechanical noises.”

This newly-developed laser falls in the category of Whispering Gallery Mode Resonators (WGM). The name comes from the whispering gallery of St. Paul’s Cathedral in London. This gallery is quite famous because verbal messages from one side of the dome can be heard at the other side of the wall. The existence of resonances (inside the dome) in the audible range are the reason for this amazing feature. However, the sensor of this lasing system resonates at frequencies as low as vibrational ones. Yang explained why they used phonon laser over photon laser in the following words:

We use the phonon laser system rather than the photon laser to demonstrate our main results because it is easier to check the linewidth of the phonon laser compared with that of the photon laser.”

An Exceptional Point in a physical field is achieved when two complex eigenvalues and their corresponding eigenvectors become one and the same thing. In recent past, it has helped researchers in a number of counterintuitive experiments and studies and scientists believe that it has a lot more to show. It is often referred to as a complex, super-energy mode where counterintuitive and unpredictable phenomena occur.

In this study, mathematical tools were used to describe the physical system. Yang told the world that they placed two WGM micro-resonators near each other in a field with two photon detectors. Both these detectors were attached to each other through a wave guide which was responsible for bringing light in and out of the system. She named them as Resonator 1 and Resonator 2 and said,

In the first resonator, which supports photons and produces phonons, we know when the light field is strong enough the radiation will trigger the mechanical oscillation related to the acoustic wave vibration. We calibrated the acoustic wave frequency at 10 megahertz. Then we adjusted the gap between the two resonators to look at the transmission spectrum of the coupled resonators. When we changed the gap, we found that we could tune the spectral distance. We tuned it from 100 megahertz, to 80 to 50 depending on the physical gap between the resonators. If you tune the gap nicely to match the spectral distance between the two to the frequency of the mechanical vibration, then you have resonance.”

The energy levels and frequencies of both these light fields is different to ensure 10 megahertz difference between these super modes. Both of them support photons but only one of them has the ability to produce phonons. Yang is pretty hopeful that phonon lasing will continue to surprise us in the future as she declared that its future is very bright.

Computer Scientist by qualification who loves to read, write, eat, and travel

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