This is a type of laser in which the active material is a dye dissolved in a suitable solvent (e.g.Rhodamine G in a methanol). The dye is excited by an external source.

The solvent broadens the states into bands and consequently laser action can be obtained over a range of wavelengths. This allows one to select a specific wavelength and to change the wavelength of the laser. Such a device is called a tunable laser.

Dye lasers are also used in producing very short pulses of radiation.

The technique is to use a dye that stops absorbing radiation when a high proportion of its molecules become excited. The cavity then becomes resonant and a pulse of radiation is produced. This technique can give pulses of about – nanoseconds duration and is used in femtochemistry.