A team of international researchers led by engineers at Washington University in St. Louis has developed a tuneable laser capable of producing phonons – tiny packets of mechanical energy produced by oscillations or vibrations. According to the researchers, these phonons could have applications in medical surgery, materials science and communications.
The research, published in Nature Photonics in July and involving collaborators from China, Austria, Japan and Michigan, USA, provides direct evidence for the first time that exceptional point-enhanced optical noises can be transferred directly to mechanical noises.
‘We've shown that you can use a light field to trigger the mechanical movement that will generate an acoustic (sound) wave,’ said Lan Yang a professor of Electrical and Systems Engineering and Washington University in St. Louis. ‘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.’
The phonon laser belongs to a category of devices called whispering gallery mode resonators (WGM), which work in a similar way to the famous whispering gallery in St. Paul's Cathedral in London – where someone on the one side of the dome can hear a message spoken to the wall by someone on the other side. Unlike the dome, however, which has resonances or sweet spots in the audible range, the sensors of the researchers’ system resonates at light frequencies and now at vibrational or mechanical frequencies.
The research group are the first to broaden what is called a laser linewidth in the phonon laser and steer it through a physical system known as the ‘exceptional point.’
Linewidth is a key component of lasing, showing the physical integrity of the lasing signal as well as the measure of usually unwanted noise in the laser.
The exceptional point can be thought of as a complex, super-energy mode where often unpredictable and counterintuitive phenomena occur. It has already contributed to a number of counterintuitive activities and results in recent physics studies.
--
Paper: Jing Zhang et al. A phonon laser operating at an exceptional point, Nature Photonics (2018). DOI: 10.1038/s41566-018-0213-5
