Scientists at The University of Nottingham, in collaboration with colleagues in the Ukraine, have produced an acoustic laser device called a saser that is the first to emit in the terahertz range. While a laser (Light Amplification by the Stimulated Emission of Radiation) uses packets of electromagnetic vibrations called photons, the saser uses sound waves composed of sonic vibrations called phonons (see "'Saser' is resonant acoustic device").
In a laser, the photon beam is produced by stimulating electrons with an external power source so they release energy when they collide with other photons in a highly reflective optical cavity. This produces a coherent and controllable shining beam of laser light in which all the photons have the same frequency and rate of oscillation. The saser mimics this technology but using sound, to produce a sonic beam of phonons that travel, not through an optical cavity like a laser, but through a tiny manmade superlattice composed of around 50 super-thin sheets of two alternating semiconductor materials, gallium arsenide and aluminum arsenide, each layer just a few atoms thick. When stimulated by a power source (a light beam), the phonons multiply, bouncing back and forth between the layers of the lattice, until they escape out of the structure in the form of an ultrahigh frequency phonon beam.
A key factor in this new science is that the saser is the first device to emit sound waves in the terahertz frequency range. One example of its potential is as a sonogram, to look for defects in nanometer-scale objects like micro-electric circuits. Another idea is to convert the saser beam to THz electromagnetic waves for medical imaging and security screening.
The research team at Nottingham, with help from Borys Glavin of the Lashkarev Institute of Semiconductor Physics in the Ukraine, has won the immediate accolade of the publication of their paper on the saser experiments in this month's Physical Review. The team also won a grant of just over a million dollars from the Engineering and Physical Sciences Research Council to develop saser technology over the next four years.
For more information, go to http://communications.nottingham.ac.uk/News/Article/A-sonic-boom-in-the-world-of-lasers.html.
