clustering (original) (raw)

Author: the photonics expert (RP)

Definition: the tendency e.g. of laser-active ions in laser gain media to form clusters in their host medium

Category: optical materials

Related: laser gain mediadoped insulator lasersquenchingupconversionenergy transferdoping concentration

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DOI: 10.61835/u0n Cite the article: BibTex BibLaTex plain textHTML Link to this page! LinkedIn

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What is Clustering of Ions?

In the context of laser physics, clustering is the tendency of laser-active ions in a solid-state doped insulator laser gain medium to form clusters, rather than to be randomly spread. This is normally an undesirable effect, as it allows for energy transfers between laser ions which can seriously degrade the laser gain and the power efficiency by processes which are called quenching. For example, this can occur in erbium-doped laser gain media with high erbium concentration (e.g. in some erbium-doped fiber amplifiers). Here, there are e.g. energy transfers involving two erbium ions which are initially in the upper laser level, where then one of the ions reaches the ground state and transfers its energy to the second ion. The latter ion will quickly relax to the upper laser level, and effectively one of the two excitations is lost. The (often weak) population in a high-lying state leads to some upconversion fluorescence. Note that the strength of such fluorescence may not be a reliable indicator of how strong upconversion effects are, since the quantum efficiency of its generation may vary a lot.

The simplest way to avoid clustering is to keep the doping concentration low. However, high doping concentrations are desirable in some situations, e.g. when a short fiber laser or amplifier must be constructed. In that case, it is important to select a host material with a high solubility of the dopant. For example, phosphate glasses allow for higher erbium concentrations without clustering, compared with silicate glasses.

Frequently Asked Questions

What is ion clustering in laser science?

In laser science, ion clustering is the tendency of laser-active ions in a solid-state gain medium to form small groups instead of being randomly distributed throughout the host material.

Why is ion clustering a problem for lasers?

Ion clustering allows for unwanted energy transfers between nearby ions, a process called quenching. This degrades laser performance by reducing the laser gain and power efficiency, as stored energy is lost.

How can ion clustering be prevented or reduced?

Clustering can be minimized by keeping the doping concentration low. Alternatively, one can select a host material with a high solubility for the dopant ions, such as using phosphate glasses for high concentrations of erbium.

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