Lasers have three basic elements-an active medium, a resonator cavity, and an excitation mechanism 141. These three elements, together with safety and control adaptations, are secured within an outer console.Lasers are characterized by their active medium. First, depending upon the physical state of this substance, lasers are described as solid, liquid, or gas. Second, because the spectrum of wavelengths emitted by each element is unique, lasers are also named by the active medium from which they were generated. It must be remembered that visible light is only one small portion of an electromagnetic spectrum that spans from the long wavelengths of radio to the very short waves of X-rays and beyond (Fig. 3). Theoretically, a laser Accepted for publication October 4, 1994. Address reprint requests to Richard Reid, M.D., who is now at the Carson Centre, 29355 Northwestern Hwy. #210, Southfield, MI 48034. 0 1995 Wiley-Liss, Inc. 202 Reid and Absten 204 Reid and Absten Frequency. Hz Wavelength, m 1 MHz 1023 1019 1077 208
Reid and AbstenUltrapulse'") has produced a laser capable of sustaining average powers in superpulsed mode that were hitherto unobtainable [91.NdYAG. The neodymium:glass laser was discovered in 1961; however, the low thermal conductivity of glass posed operating problems. Hence, neodymium was doped into yttrium aluminum garnet and placed in a reflective optical cavity with krypoton arc flashlamps as the excitation source. Nd:YAG lasers emit near infrared radiation at 1.06 pm, with an operating power up to 120 watts. Early model Nd:YAG lasers required 230 volts, three phase electricity, and water cooling. However, there are now more efficient models, which utilize 115 volt power sources and air cooling. In addition to operating the Nd:YAG laser in continuous wave manner, this instrument can be configured to operate in superpulsed or Q-switched mode, thus producing very different types of tissue interactions.Erbium:YAG. In the future, erbium:YAG lasers may allow even more precise surgery upon aqueous tissues [lo]. The Er:YAG laser emits high energy pulses of midinfrared light with a wavelength of 2,940 nanometers (2.9 pm). The peak absorption of light in water occurs in the 2.9 pm range, making the Er:YAG laser energy even more highly absorbed in aqueous tissues than CO, laser energy (at 10.6 pm). The combination of high water affinity and high fluence pulses produces an exceptionally narrow zone of damage around the vaporization crater. Hence, the Er: YAG has been tried for corneal resculpting, a task generally reserved for the excimer laser. The Er: YAG laser is also very highly absorbed by osseous minerals, making it a highly precise drill and saw for bone surgery and dentistry.Ho1mium:YAG. The most recent addition to the growing array of surgical lasers is the holmium:YAG laser, which emits 0.25 millisecond pulses of midinfrared energy (2.1 pm). The laser medium is holmium, a rare earth element, within an yttrium aluminum garnet crystal. The holmium:YAG laser is excited by a xenon arc flashlamp and ...