# linewidth

## Linewidth

A measure of the width of the band of frequencies of radiation emitted or absorbed in an atomic or molecular transition. One of the dominant sources of electromagnetic radiation of all frequencies is transitions between two energy levels of an atomic or molecular system. The frequency of the radiation is related to the difference in the energy of the two levels by the Bohr relation (1),

(1)
where ν0 is the frequency of the radiation, h is Planck's constant, and E1 and E2 are the energies of the levels. This radiation is not monochromatic, but consists of a band of frequencies centered about ν0 whose intensity I(ν) can be characterized by the linewidth. The linewidth is the full width at half height of the distribution function I(ν). The simplest case is for a transition from an excited state to the ground state for an atom or molecule at rest. For this case, the normalized distribution function is the lorentzian line profile given by Eq. (2).
(2)
Here Δν is the full width at half maximum (FWHM). The FWHM is related to the lifetime τ of the excited level through Eq. (3).
(3)
This is a manifestation of the quantum-mechanical uncertainty principle, and the linewidth Δν is referred to as the natural linewidth. See Energy level (quantum mechanics), Quantum mechanics, Uncertainty principle

Another major source of line broadening for atomic and molecular transitions is the Doppler shift due to thermal motion. For most situations the Doppler width is greater than the natural linewidth. See Doppler effect

A third major source of line broadening is collisions of the radiating molecule with other molecules. This broadens the line, shifts the center of the line, and shortens the lifetime of the radiating state.

For radiating atoms in a liquid or solid the width is usually dominated by the strong interaction of the radiator with the surrounding molecules. The net result is a broad line profile with a complex structure. See Band theory of solids

## linewidth

[′līn‚width]
(atomic physics)
A measure of the width of the band of frequencies of radiation emitted or absorbed in an atomic or molecular transition, given by the difference between the upper and lower frequencies at which the intensity of radiation reaches half its maximum value.
References in periodicals archive ?
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Yizhi Liang, assistant professor at the Institute of Photonics Technology, explained that fibre lasers such as this --which have a kilohertz-order linewidth --can be exploited as sensors due to their ability to offer a high signal-to-noise ratio.
The Single Frequency DPSS laser--Solo 640--exhibits excellent performance characteristics (beam quality, wavelength and power stability) and is particularly suited for holography, which depends on the power, stability and linewidth of a laser to give clear images with a deep field of view.
At the CS, the lightwave is generated from an external-cavity laser (ECL) at 193.26 THz with a 100 MHz linewidth, which is divided into two parts by an optical power splitter.
In order to achieve different memories, we choose a narrow linewidth laser delivering 100 ns, 15 ns, and 0.7 ns pulses of a 100 [mu]J energy as the pump while the Stokes pulse power is equal to 10 W.
The surface resistance is proportional to the resistivity of the material and is inversely proportional to the thickness and linewidth. The frequency-selective surface is printed with a thin ink layer to produce a uniform sheet of security paper; we designed a Jerusalem structure with a thick line width.
Parameter Value Test wavelength 850 nm Operating wavelength 1550 nm Operating temperature 25[degrees]C Threshold current 1.49538 mA FWHM linewidth 10 MHz Linear output power 0.35 mW Turn on delay 1.73287 ns P-I slope 0.23405 mW/mA Relative intensity noise -150 dB/Hz Table 2: Different parameters for MMF.
The difference is that the coherent [PHI]-OTDR requires a light source with a longer coherence length and narrower linewidth. The light from a coherent light source is modulated using an external modulator, and it is converted to continuous short optical pulse trains.
Dixson, "Higher order tip effects in traceable CD-AFM-based linewidth measurements," Measurement Science and Technology, vol.
These synthesized PEG-Gds were also evaluated by the linewidth at half height of each PEG contrast agent through NMR measurements to investigate the cause of the contrast agent enhancement.

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