Laser-induced fluorescence (LIF) is a spectroscopic method.

The preferred specie is excited with help of a laser. The wave length is often selected to be the one at which the specie has its largest cross section. The excited specie will after some time, usually in the order of micro seconds, de-excite and emit light. This light, fluorescence, is measured.

Two different kinds of spectra exists, LIF-spectra and excitation scans.

The LIF-spectra are performed with a fixed lasing wave length, as above and the fluorescence spectrum is analyzed. Excitation scans on the other hand collect all fluorescent light, without measuring the wavelength. Instead the lasing wave length is changed.

The advantage over absorption spectroscopy is that it is possible to get two- and three-dimensional images since fluorescence takes place in all directions. It is also possible to distinguish between more species, since both the lasing wave length and the measured wave length can be changed.