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),

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).
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).
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


(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 ?
Tenders are invited for Narrow Linewidth 785Nm Diode Lasers
The new design allows for narrower open-loop linewidth (10 MHz over a 1 s integration time) and reduced jitter both at a single wavelength and while scanning.
Active optical clocks provide several new possibilities of applications: (i) more stable optical clock than any current atomic clocks; (ii) sub-natural linewidth laser spectroscopy; (iii) long coherence time laser with linewidth at mHz level; (iv) Ramsey laser combining stimulated emission process and Ramsey separated oscillatory fields method," commented Professor Yiqiu Wang.
Lasers should have an extra-cavity output power of at least 100 mW and linewidth of not more than 200 kHz @ 1 us free running.
NeoPhotonics is a supplier to Huawei of Access products designed for its Broadband FTTx systems and of advanced WDM Transport products, such as integrated coherent receivers and narrow linewidth tunable lasers designed for its 40G and 100G Coherent transport systems.
They examine linewidth broadening, widely tunable monolithic laser diodes, practical issues, related DWDM sources, communications applications and requirements, and other applications.
CD-SEM images of linewidth test patterns were analyzed to determine the lines' widths and the angles of their edges.
One of these properties is that the linewidth enhancement factor of a QCL is close to zero, compared to two to five for a conventional laser.
The battle between metal mesh suppliers will be fought on narrowing the linewidth and improving throughput and yield (biggest cost unknown/driver).
This is the first test of the library-based shape-sensitive linewidth measurement method on nested lines.
The NMR detection coil mounted is made of susceptibility matched material capable of shimming solution linewidth
In addition, NeoPhotonics is showcasing its broad line of active and passive optical components, modules and subsystems for optical network segments, including: Integrated Coherent Receivers (ICR) and Narrow Linewidth Tunable Lasers (NLW-TL) for coherent 40 Gbps and 100Gbps systems; 40Gbps and 100Gbps CFP modules, SFP, SFP+ and XFP transceivers; GPON, GEPON, 10GPON and NGPON OLTs; Athermal Arrayed Waveguide Gratings (AWG); and Multicast Switches, at the OFC/NFOEC Conference and Exposition at the Los Angeles Convention Center, Booth 2200, March 6 - 8, 2012.