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
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.
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.