What is Laser Induced Fluorescence?

Laser Induced Fluorescence (LIF) is a highly sensitive optical spectroscopic technique in which a sample becomes excited with a laser, and the consequent fluorescence emitted by the specimen is captured by a photodetector. Its imaging techniques are used for mixture fraction and temperature measurements in fluid mechanics, species concentration, sprays and combustion systems, and classification of viruses. LIF is also widely used for the analysis of flames. In medicine, LIF can be used to detect endogenous fluorophores for detection of neoplasms (e.g. lung cancer, and dermatological diseases). 

LIF imaging provides a high spatial and temporal resolution, and is also molecule specific. LIF is a two step process: absorption of a laser photon, followed by emission of a fluorescent photon from the excited state. For the photon to be absorbed, the laser lambda wavelength must be fixed to the allowed energy transition of the LIF-active atom. Then, an optical filter selects red-shifted fluorescence light and becomes converted to the camera signal. The fluorescent light is usually measured with a photomultiplier tube (PMT) or filtered photodiodes. Thus, Laser Induced Fluorescence provides a high selectivity; it can capture specific species to emit light in environments where many other species are present. This is because the lasting wavelength can be altered to a specific excitation of a given species. LIF also has a high signal-to-noise ratio.