Nd:YAG 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.
Nd:Cr:YAG 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.
Er:YAG 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 pink.
Yb:YAG Ytterbium-doped YAG (
Yb:YAG) is an active laser medium lasing at 1030 nm, with a broad, 18 nm wide absorption band at 940 nm. It is one of the most useful media for high-power
diode-pumped solid state lasers. The dopant levels used range between 0.2% and 30% of replaced yttrium atoms. Yb:YAG has very low fractional heating, very high
slope efficiency, and no excited-state absorption or up-conversion, high mechanical strength and high thermal conductivity. Yb:YAG can be pumped by reliable
InGaAs laser diodes at 940 or 970 nm. Yb:YAG is a good substitute for 1064 nm Nd:YAG in high-power applications, and its frequency-doubled 515 nm version can replace the 514 nm
argon lasers.
Nd:Ce:YAG Neodymium-
cerium double-doped YAG (
Nd:Ce:YAG, or
Nd,Ce:YAG) is an active laser medium material very similar to Nd:YAG. The added cerium atoms strongly absorb in the
ultraviolet region and transfer their energy to the neodymium atoms, increasing the pumping efficiency; the result is lower thermal distortion and higher power output than Nd:YAG at the same pumping level. The lasing wavelength, 1064 nm, is the same as for Nd:YAG. The material has a good resistance to damage caused by UV from the pump source, and low
lasing threshold. Usually 1.1–1.4% of Y atoms are replaced with Nd, and 0.05–0.1% with Ce.
Ho:Cr:Tm:YAG Holmium-
chromium-
thulium triple-doped YAG (
Ho:Cr:Tm:YAG, or
Ho,Cr,Tm:YAG) is an active laser medium material with high efficiency. It lases at 2080 nm and can be pumped by a flashlamp or a laser diode. It is widely used in military, medicine, and meteorology. It works well at room temperature, has high
slope efficiency, and operates at a wavelength where the threshold for eye damage is relatively high. When pumped by a diode, the 785 nm band for Tm3+ ion can be used. 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, high-energy
gamma radiation and
charged particle detectors, and high-resolution imaging screens for gamma,
x-rays,
beta radiation and
ultraviolet radiation. Ce:YAG can be further doped with
gadolinium. ==See also==