What is the medical Laser ?<br /><br />Lasers have been used for various medical procedures such as<br />dermatology and cosmetic surgery, wound healings , nerve<br />stimulation, dentistry ophthalmology applications for<br />vision corrections and corneal deceases. and many other<br />therapeutic procedures. Combining the nanoparticles, diode lasers<br />have been also used for cancer therapy, bio-sensing, bio-imaging,<br />drug delivery and diagnostics of cancer cell.<br />Lasers in the near infrared (IR), wavelength of (750-1200) nm, have<br />deeper tissue penetration depths than that of visible lasers. Therefore,<br />near IR lasers are good candidates for procedures which need deep<br />penetrations such as hair removal and nano-gold mediated<br />cancer therapy. On the other hand, visible lasers (430 – 680) nm<br />with strong absorption in blood and color-dyes have been used for<br />phototherapy of oral cancer, retina deceases and tattoo removal.<br />Mid-IR lasers (1.9-3.0) um and (9.3 -10.6) um with strong absorption<br />in water and tissue have been used for super surface procedures<br />or ablative type procedures such as soft and hard tissue ablation. Other<br />IR lasers (1.3-1.6) um have been used for so called minimally invasive<br />procedures such as resurfacing due to their smaller tissue absorption<br />than that of mid-IR lasers.<br />In this review article, the fundamental principles behind the<br />medical laser applications will be presented, including the laser<br />spectra of UV (200-400) um, visible (400-700) nm, near-IR (700-<br />2900) nm, and mid-IR (3-5) um having various penetration depths<br />which define invasive and noninvasive procedures. Diode lasers for<br />various surgical procedures including soft tissue cutting, coagulation<br />and cancer thermal therapy will be reviewed. Various photosensitizers<br />are presented in matching the laser absorption wavelengths. Finally,<br />the principles and applications of photothermal therapy (PTT) and<br />photodynamic therapy (PDT).<br /><br />basic definition and units<br />Most lasers are defined by their output “colors”, i.e, wavelength (or<br />spectrum)<br />as follows:<br />UV (200-400) um, visible (400-700) nm, near-IR (700-2900) nm, and<br />mid-IR, (3-5) um, where 1 um=1,000 nm.<br />The output of a laser is defined by the following units:<br />Power (P) in mW (or W), 1W=1,000 mW.<br />Intensity (I) in mW/cm2 (power density per unit area).<br />Energy (E) in mJ; Fluence (F) in mJ/cm2 (energy density).<br /><br />Laser-matter interaction<br />Laser-tissue (or other media) interaction, in general, could be<br />categorized into three processes: (a) pure thermal, (b) non-thermal,<br />and (c) combined thermal and non-thermal effects