Yttrium aluminium garnet

Yttrium aluminum garnet (YAG, Y3Al5O12) is a synthetic crystalline material of the garnet group. It is a cubic yttrium aluminum oxide phase, with other examples being YAlO3 in a hexagonal or an orthorhombic, perovskite-like form, and the monoclinic Y4Al2O9. Yttrium aluminum garnet (YAG, Y3Al5O12) is a synthetic crystalline material of the garnet group. It is a cubic yttrium aluminum oxide phase, with other examples being YAlO3 in a hexagonal or an orthorhombic, perovskite-like form, and the monoclinic Y4Al2O9. YAG, like garnet and sapphire, has no uses as a laser medium when pure. However, after being doped with an appropriate ion, YAG is commonly used as a host material in various solid-state lasers. Rare earth elements such as neodymium and erbium can be doped into YAG as active laser ions, yielding Nd:YAG and Er:YAG lasers, respectively. Cerium-doped YAG (Ce:YAG) is used as a phosphor in cathode ray tubes and white light-emitting diodes, and as a scintillator. YAG for a period was used in jewelry as a diamond and other gemstone simulant. Colored variants and their doping elements include: green (chromium), blue (cobalt), red (manganese), yellow (titanum), purple (neodymium), pink, and orange. As faceted gems they are valued (as synthetics) for their clarity, durability, high refractive index and dispersion. The critical angle of YAG is 33 degrees. YAG cuts like natural garnet, with polishing being performed with alumina or diamond (50,000 or 100,000 grit) on common polishing laps. YAG has low heat sensitivity. As a synthetic gemstone YAG has numerous varietal and trade names, as well as a number of misnomers. Synonymous names include: alexite, amamite, circolite, dia-bud, diamite, diamogem, diamonair, diamone, diamonique, diamonite, diamonte, di'yag, geminair, gemonair, kimberly, Linde simulated diamond, nier-gem, regalair, replique, somerset, triamond, YAIG, and yttrium garnet. Production for the gem trade decreased after the introduction of synthetic cubic zirconia; as of 1995 there was little production. Some demand exists as synthetic garnet, and for designs where the very high refractive index of cubic zirconia is not desirable. Neodymium-doped YAG (Nd:YAG) was developed in the early 1960s, and the first working Nd:YAG laser was invented in 1964. Neodymium-YAG is the most widely used active laser medium in solid-state lasers, being used for everything from low-power continuous-wave lasers to high-power Q-switched (pulsed) lasers with power levels measured in the kilowatts. The thermal conductivity of Nd:YAG is higher and its fluorescence lifetime is about twice as long as that of Nd:YVO4 crystals, however it is not as efficient and is less stable, requiring more precisely controlled temperatures. The best absorption band of Nd:YAG for pumping the laser is centered at 807.5 nm, and is 1 nm wide. Most Nd:YAG lasers produce infrared light at a wavelength of 1064 nm. Light at this wavelength is rather dangerous to vision, since it can be focused by the eye's lens onto the retina, but the light is invisible and does not trigger the blink reflex. Nd:YAG lasers can also be used with frequency doubling or frequency tripling crystals, to produce green light with a wavelength of 532 nm or ultraviolet light at 355 nm, respectively. The dopant concentration in commonly used Nd:YAG crystals usually varies between 0.5 and 1.4 molar percent. Higher dopant concentration is used for pulsed lasers; lower concentration is suitable for continuous-wave lasers. Nd:YAG is pinkish-purple, with lighter-doped rods being less intensely colored than heavier-doped ones. Since its absorption spectrum is narrow, the hue depends on the light under which it is observed. YAG doped with neodymium and chromium (Nd:Cr:YAG or Nd/Cr:YAG) has absorption characteristics which are superior to Nd:YAG. This is because energy is absorbed by the broad absorption bands of the Cr3+ dopant and then transferred to Nd3+ by dipole-dipole interactions. This material has been suggested for use in solar-pumped lasers, which could form part of a solar power satellite system. Erbium-doped YAG (Er:YAG) is an active laser medium lasing at 2940 nm. Its absorption bands suitable for pumping are wide and located between 600 and 800 nm, allowing for efficient flashlamp pumping. The dopant concentration used is high: about 50% of the yttrium atoms are replaced. The Er:YAG laser wavelength couples well into water and body fluids, making this laser especially useful for medicine and dentistry uses; it is used for treatment of tooth enamel and in cosmetic surgery. Er:YAG is used for noninvasive monitoring of blood sugar. The mechanical properties of Er:YAG are essentially the same as Nd:YAG. Er:YAG operates at wavelengths where the threshold for eye damage is relatively high (since the light is absorbed before striking the retina), works well at room temperature, and has high slope efficiency. Er:YAG is pale green.