Sound Amplification by Stimulated Emission of Radiation
Encyclopedia
A SASER is the acoustic analogue of the laser
. It is capable of producing highly coherent, concentrated beams of ultrasound
, using methods very similar to those employed in the laser. First experimentally demonstrated in the Gigahertz range in 2009, the SASER is being developed at the University of Nottingham
, the Lashkarev Institute of Semiconductor Physics, and Caltech. The University of Nottingham device operates at about 440 GHz, while the Caltech device operates in the megahertz range. In an interview, a member of the Nottingham group, told physicsworld.com that "the two approaches are complementary and it should be possible to use one device or the other to create coherent phonons at any frequency in the megahertz to terahertz range."
wafers are placed in a lattice within an acoustically reflective chamber. Upon the addition of electron
s, short-wavelength (in the terahertz range) phonon
s are produced. Since the electrons are confined to the quantum wells existing within the lattice, the transmission of their energy depends upon the phonons they generate. As these phonons strike other layers in the lattice, they excite electrons, which produce further phonons, which go on to excite more electrons, and so on. Eventually, a very narrow beam of high-frequency ultrasound
exits the device.
A second meaning of SASER is the thermoacoustic laser. This is a half-open pipe with a heat differential across a special porous material inserted in the pipe. Much like a light LASER, a thermoacoustic SASER has a high-Q cavity and uses a gain medium to amplify coherent waves. See thermoacoustic heat engine.
, as a method of signal modulation and/or transmission.
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
. It is capable of producing highly coherent, concentrated beams of ultrasound
Ultrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...
, using methods very similar to those employed in the laser. First experimentally demonstrated in the Gigahertz range in 2009, the SASER is being developed at the University of Nottingham
University of Nottingham
The University of Nottingham is a public research university based in Nottingham, United Kingdom, with further campuses in Ningbo, China and Kuala Lumpur, Malaysia...
, the Lashkarev Institute of Semiconductor Physics, and Caltech. The University of Nottingham device operates at about 440 GHz, while the Caltech device operates in the megahertz range. In an interview, a member of the Nottingham group, told physicsworld.com that "the two approaches are complementary and it should be possible to use one device or the other to create coherent phonons at any frequency in the megahertz to terahertz range."
Physics
A SASER operates on principles remarkably similar to those of a laser. A stack of thin semiconductorSemiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
wafers are placed in a lattice within an acoustically reflective chamber. Upon the addition of electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s, short-wavelength (in the terahertz range) phonon
Phonon
In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, such as solids and some liquids...
s are produced. Since the electrons are confined to the quantum wells existing within the lattice, the transmission of their energy depends upon the phonons they generate. As these phonons strike other layers in the lattice, they excite electrons, which produce further phonons, which go on to excite more electrons, and so on. Eventually, a very narrow beam of high-frequency ultrasound
Ultrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...
exits the device.
A second meaning of SASER is the thermoacoustic laser. This is a half-open pipe with a heat differential across a special porous material inserted in the pipe. Much like a light LASER, a thermoacoustic SASER has a high-Q cavity and uses a gain medium to amplify coherent waves. See thermoacoustic heat engine.
Uses
Apart from allowing the investigation of terahertz-frequency ultrasound, the SASER is also likely to find myriad uses in optoelectronicsOptoelectronics
Optoelectronics is the study and application of electronic devices that source, detect and control light, usually considered a sub-field of photonics. In this context, light often includes invisible forms of radiation such as gamma rays, X-rays, ultraviolet and infrared, in addition to visible light...
, as a method of signal modulation and/or transmission.