Dye lasers use organic materials that generally emit in the visible spectrum and are thus coloured. These molecules are diluted in a solvent (usually an alcohol, like ethylene glycol or methanol).
The pump source of dye lasers is optical: either an arc lamp or, in the majority of cases, another laser (gas or solid state).
The whole of the visible spectrum is covered. In fact, the dyes are complex organic molecules that have many energy levels. The levels are so close together that they are considered as an energy band. In general, a molecule of dye covers continuously a region of about fifty nanometres in the visible. Dye lasers are the only ones to cover the visible spectrum entirely. Despite these interesting properties, dye lasers are little used because their implementation is impractical: to prevent the molecules from being destroyed by the pump source, the dye circulates in the pumping zone from a reservoir. In addition, the dye and solvent mixture degrades with time and must be changed regularly.