Lasers with Solid State Lasing Mediums
For an active medium, the solid state laser uses lasing ions which are suspended in a rod shaped solid matrix. These "dopants" in the rod are excited by a source of intense light. This may be either one or two cylindrical flash lamps or a helical flash lamp which surrounds the rod. If two cylindrical flash lamps are used, the laser rod is placed between them at the common focus of two ellipses whose other foci determine the placement of the flash lamps.
The distance between foci, in each of the two ellipses, sharing a common focus, is defined by the configuration of an elliptical reflector that surrounds the excitation sources and the laser rod. The arrangement provides an efficient coupling of excitation light into the lasing medium. A water cooling syst em controls the temperature of the rod and flash lamps.
Three major representatives of this type of laser are made of synthetic ruby, of neodymium; glass (Nd: Glass), and Neodymium Doped Yttrium Aluminium Garnet (Nd:YAG). In each of these materials, lasing ions exist as minority dopants in the host matrix. For all the three, flash lamp Nlife is limited and operating costs are higher than for CO2 lasers, but certain advantages remain. Solid state lasers can be operated in several ways. One way is the excitation of the lasing medium (rod) with capacitate discharge through the flash lamp(s), which results in the emission of a brief flash of light. This in turn excites the lasing medium into emitting a burst of light. For Nd:YAG this occurs at a wavelength of 1.064 m. Using this excitation scheme allows pulses that lie between 0.2 and 12.0 milliseconds, at repetition rates up to 100 pulses per second. At slower rates, the TEM multimode energy in each output pulse may be 20 joules or more for a typical commercially available laser; while at the most rapid rates, this will fall to approximately 2 joules per pulse.
Even at the highest repetition rates, the energy in each pulse is sufficient for drilling and spot welding metals. Since, the wavelength of light emitted by a Nd:YAG laser is relatively short, the output beam can be focused to a spot of small diameter. These flash lamp pumped lasers are capable of drilling holes as small as 0.025 mm in diameter, but they are not well suited for drilling large holes because of the non uniform distribution of energy across the output beam.