APPLICATIONS,  SAFETY,  AND  MAINTENANCE

         YAG lasers are a workhorse for many applications involving cutting, drilling, and trimming. In competition with a carbon dioxide laser for many applications, the short pulse length possible with a Q-switched YAG laser makes it ideal for many applications where the CW carbon dioxide laser is not optimal. Most YAG lasers for materials processing have Q-switches already installed at the factory. For drilling applications, especially in metals, the fast pulse ablates materials without creating heat in the substrate being drilled. For semiconductor processing, the fast pulse allows a tiny amount of resistor material to be obliterated without heating the surrounding material and hence affecting the properties of the material. YAG lasers also work well for many marking applications.

       In the entertainment industry, frequency-doubled YAG lasers have been used for numerous laser light displays, especially high-power applications such as cloud writing, where they offer an alternative to argon-ion lasers. The lack of an inexpensive solid-state CW red or blue laser, though, as well as a laser that oscillates on several wavelengths simultaneously, precludes the use of solid-state lasers for full-color displays, where the krypton-ion laser is still commonly used (although this situation may change as the development of solid-state lasers progresses and new materials operating at new wavelengths are found).

         Maintenance involves the usual cleaning of laser optics (required with essentially all lasers) as well as periodic lamp changes and maintenance of the cooling-water system. Cooling-water systems usually use deionized water in an inner loop that floods the lamp and rod. Heat from the inner loop is then changed with a supply of city water. A deionizing filter keeps the inner water clean since the accumulation of ions results in conduction that will short the lamp and corrode metal parts such as reflectors. Filters must be changed periodically, and many lasers have a safety feature that shuts down the system if the conductivity of the cooling water exceeds a safe value.

       Although the danger involved in most lasers (including high voltages in the power supplies and ocular hazards from powerful beams) is quite apparent, there are a few precautions worth noting with regard to the YAG laser. This is perhaps one of the most dangerous lasers from an eye-safety standpoint. Because the wavelength penetrates the eye readily and Q-switched laser pulses can damage tissue rapidly (the blink response being ineffective), this laser is probably responsible for more eye injuries than any other! Combine this with an equally (if not more) dangerous SHG output at 532 nm and you’ve got a laser worthy of great respect. Safety glasses are mandatory since even a specular reflection can be damaging. Unfortunately, glasses used with these lasers must block both IR and green light with a large attenuation factor [or optical density (marked OD on the glasses)], so it is usually required to obtain glasses specially designed for use with a SHG YAG laser. Broadband glasses designed for use with many lasers are generally not designed to block both wavelengths effectively. Be careful around these lasers!

         A further warning regarding the handling of high-pressure arc lamps: Because of the high pressures, the lamps have a tendency to explode during lamp changes. This author has had numerous lamps explode, especially when old lamps are removed, since they tend to be weakened, due to stress generated during operation. Protection from flying glass is mandatory when relamping a lamp-pumped YAG laser.