Collins English Dictionary
The ''Collins English Dictionary'' is a printed and online dictionary of English. It is published by HarperCollins in Glasgow. It was first published in 1979.
Corpus
The dictionary uses language research based on the Collins Corpus, which is ...
''. is based on the stimulated
Raman scattering
In chemistry and physics, Raman scattering or the Raman effect () is the inelastic scattering of photons by matter, meaning that there is both an exchange of energy and a change in the light's direction. Typically this effect involves vibrationa ...
(SRS) phenomenon, when a lower frequency 'signal'
photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that can ...
induces the
inelastic scattering
In chemistry, nuclear physics, and particle physics, inelastic scattering is a process in which the internal states of a particle or a system of particles change after a collision. Often, this means the kinetic energy of the incident particle is n ...
of a higher-frequency 'pump' photon in an optical medium in the nonlinear regime. As a result of this, another 'signal' photon is produced, with the surplus energy resonantly passed to the vibrational states of the medium. This process, as with other
stimulated emission
Stimulated emission is the process by which an incoming photon of a specific frequency can interact with an excited atomic electron (or other excited molecular state), causing it to drop to a lower energy level. The liberated energy transfers to ...
processes, allows all-optical amplification.
Optical fiber
An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at ...
is today most used as the nonlinear medium for SRS for telecom purposes; in this case it is characterized by a resonance frequency downshift of ~11 THz (corresponding to a wavelength shift at ~1550 nm of ~90 nm). The SRS amplification process can be readily cascaded, thus accessing essentially any wavelength in the fiber low-loss guiding windows (both 1310 and 1550). In addition to applications in nonlinear and ultrafast optics, Raman amplification is used in optical
telecommunications
Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...
, allowing all-band wavelength coverage and in-line distributed signal amplification.
See also
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Raman laser
A Raman laser is a specific type of laser in which the fundamental light-amplification mechanism is stimulated Raman scattering. In contrast, most "conventional" lasers (such as the ruby laser) rely on stimulated electronic transitions to amplify ...
Chirped pulse amplification
Chirped pulse amplification (CPA) is a technique for amplifying an ultrashort laser pulse up to the petawatt level, with the laser pulse being stretched out temporally and spectrally, then amplified, and then compressed again. The stretching and ...
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Regenerative amplification
In laser science, regenerative amplification is a process used to generate short but strong pulses of laser light. It is based on a pulse trapped in a laser resonator, which stays in there until it extracts all of the energy stored in the amplific ...