Dye laser

A dye laser is a laser which uses an organic dye as a lasing medium, usually as a liquid solution. Compared to gases and most solid state lasing media, a dye can usually be used for a much wider range of wavelengths. The wide bandwidth makes them particularly suitable for tunable lasers and pulsed lasers. Moreover, the dye can be replaced by another type in order to generate different wavelengths with the same laser, although this usually requires replacing other optical components in the laser as well.
The long-wavelength absorption band of laser dyes is attributed to the transition from the electronic ground state S0 to the first excited singlet state S1. The transition moment [[1]] for this process is typically very large, thus giving rise to an absorption band with an oscillator strength on the order of unity. The reverse process S1->S0 is responsible for the spontaneous emission known as fluorescence and for the stimulated emission in dye lasers.
Dye lasers are also used dermatologically, to make skin tone more even.

Construction
Since organic dyes tend to degrade under the influence of light, the dye solution is normally circulated from a large reservoir. The dye solution can be flowing through a cuvette, i.e., a glass container, or be as a dye jet, i.e., as a sheet-like stream in open air from a specially-shaped nozzle. With a dye jet, one avoids reflection losses from the glass surfaces and contamination of the walls of the cuvette. These advantages come at the cost of a more-complicated alignment.

Chemicals used
Some of the dyes are Rhodamine 6G, fluorescein, coumarin, stilbene, umbelliferone, tetracene, malachite green, and others.
Adamantane is added to some dyes to prolong their life.
Cycloheptatriene and cyclooctatetraene (COT) can be added as triplet quenchers for rhodamine G, increasing the laser output power. Output power of 1.4 kilowatt at 585 nm was achieved using Rhodamine 6G with COT in methanol-water solution.

From Wikipedia