[The basics of laser and its application in urology]

A laser, light amplification by stimulated emission of radiation, is a device able to transform other energies into electromagnetic radiation with emission of light beams of different wavelengths. They amplify the light and produce coherent light beams, the frequency of which varies from infrared to X ray. Stimulated emission, the process laser is based on, was described by A. Einstein in 1917, but it was not until the decade of the '60s when the first laser process was observed in a ruby crystal. Depending on the environment they use, lasers may be named as solid-state, gas, semiconductors or liquid. The possibility of uses for laser is almost unlimited, becoming a very valuable tool in biomedical sciences thanks to the various effects they produce when interacting with tissues (photovaporization, photodisruption, photocoagulation or photostimulation). For this reason, today, the use of lasers in the field of urology offers a wide range of possibilities, going from surgery for the treatment of obstruction, such as the fragmentation of a urinary stone or resection/ablation of prostatic tissue, to reconstructive surgery, such as tissue welding in vasovasostomy or urethral stenosis repair.