The powerful monochromatic radiation from argon ion lasers will excite fluorescence in small traces of many substances. This has proved to be of particular value in the detection and enhancement of latent fingerprints and other trace contact evidence. The photography of these marks is extremely important and can be difficult. Many specialised photographic techniques are used including both interference filters and sharp cut off filters, various photographic emulsions and infra red sensitive film. Hypersensitisation of the film and cooling in liquid nitrogen are used to improve the photography of weak fluorescence, various chemical treatments are also used to further enhance the fluorescence.