threshold, good thermal conductivity, good chemical stability, resists ultraviolet radiation, and is easily machinable. It is replacing more traditional Q-switching materials like lithium fluoride and organic dyes. The dopant levels used range between 0.5 and 3 percent (molar). Cr:YAG can be used for passive Q-switching of lasers that operate at wavelengths between 1000 and 1200 nm, such as those based on Nd:YAG, Nd:YLF, Nd:YVO4, and Yb:YAG. Cr:YAG can be also used as a laser gain medium itself, producing tunable lasers with outputs adjustable between 1350 and 1550 nm. The Cr:YAG laser can generate ultrashort pulses (in the femtoseconds range) when it is pumped at 1064 nm by a Nd:YAG laser. Cr:YAG has been demonstrated in an application of non-linear optics as a self-pumped phase-conjugate mirror in a Nd:YAG "loop resonator". Such a mirror provides compensation of both phase and polarization aberrations induced into the loop resonator. Dy:YAG Dysprosium-doped YAG (Dy:YAG) is a temperature-sensitive phosphor used in temperature measurements. The phosphor is excited by a laser pulse and its temperature-dependent fluorescence is observed. Dy:YAG is sensitive in ranges of 300–1700 K. The phosphor can be applied directly to the measured surface, or to an end of an optical fiber. It has also been studied as a single-phase white emitting phosphor in phosphor-converted white light-emitting diodes. Sm:YAG Samarium-doped YAG (Sm:YAG) is a temperature-sensitive phosphor similar to Dy:YAG. Tb:YAG Terbium-doped YAG (Tb:YAG) is a phosphor used in cathode ray tubes. It emits at yellow-green color, at 544 nm. Ce:YAG Cerium(III)-doped YAG (Ce:YAG or YAG:Ce) is a phosphor, or a scintillator when in pure single-crystal form, with a wide range of uses. It emits yellow light when subjected to blue or ultraviolet light or to x-rays. It is used in white light-emitting diodes as a coating on a high-brightness blue InGaN diode, converting part of the blue light into yellow, which together then appear as white. Such an arrangement gives less than ideal color rendering. The output brightness decreases with increasing temperature, further altering device color output. Ce:YAG is also used in some mercury-vapor lamps as one of the phosphors, often together with Eu:Y(P,V)O4 (yttrium phosphate-vanadate). It is also used as a phosphor in cathode ray tubes, where it emits green (530 nm) to yellow-green (550 nm) light. When excited by electrons, it has virtually no afterglow (70 ns decay time). It is suitable for use in photomultipliers. Ce:YAG is used in PET scanners,