Collins English Dictionary
The ''Collins English Dictionary'' is a printed and online dictionary of English. It is published by HarperCollins in Glasgow.
The edition of the dictionary in 1979 with Patrick Hanks as editor and Laurence Urdang as editorial director, was ...
''. is based on the stimulated
Raman scattering
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 vibrational energy being gained by a ...
(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, so they always ...
induces the
inelastic scattering In chemistry, nuclear physics, and particle physics, inelastic scattering is a fundamental scattering process in which the kinetic energy of an incident particle is not conserved (in contrast to elastic scattering). In an inelastic scattering proces ...
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 processes, allows all-optical amplification.
Optical fiber
An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means to ...
is today mostly 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 is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...
, 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 Raman effect#Stimulated Raman scattering and Raman amplification, stimulated Raman scattering. In contrast, most "conventional" lasers (such as the r ...
Chirped pulse amplification
Chirped pulse amplification (CPA) is a technique for amplifying an ultrashort pulse, 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 ...
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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 amplifi ...