Yttrium aluminium garnet
Encyclopedia
Yttrium aluminium garnet (YAG, Y
3Al
5O
12) is a synthetic crystal
line material of the garnet
group. It is also one of three phases of the yttria-aluminium composite, the other two being yttrium aluminium monoclinic (YAM) and yttrium aluminium perovskite (YAP). YAG is commonly used as a host material in various solid-state laser
s. 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 (YAG:Ce) is used as a phosphor
in cathode ray tube
s and white light-emitting diode
s, and as a scintillator
.
and other gemstone
simulant. Colored variants and their doping elements include: green (chromium
), blue (cobalt
), red (manganese
), yellow (titanium
), 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 similar to natural garnet
, with polishing being performed with alumina or diamond
(50,000 or 100,000) 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
; 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.
-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 laser
s, 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 crystal
s, 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.
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 laser
s, which could form part of a solar power satellite system.
-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.
-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 0.2-30% 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 diode
s 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.
-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.
-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 2097 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 781 nm band is used. Other major pump bands are located between 400 and 800 nm. The dopant levels used are 0.35 atom.% Ho, 5.8 atom.% Tm, and 1.5 at.% Cr. The rods have green color, imparted by chromium(III).
-doped YAG (Tm:YAG) is an active laser medium that operates between 1930 and 2040 nm. It is suitable for diode pumping. A dual-mode Tm:YAG laser emits two frequencies separated by 1 GHz.
(IV)-doped YAG (Cr:YAG) provides a large absorption cross section in the 0.9-1.2 micrometer spectral region, which makes it an attractive choice as a passive Q-switch for Nd-doped lasers. The resulting devices are solid-state, compact and low-cost. Cr:YAG has high damage 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 dye
s. 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 laser
s with outputs adjustable between 1350 and 1550 nm. The Cr:YAG laser can generate ultrashort pulse
s (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.
-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
.
-doped YAG (Sm:YAG) is a temperature-sensitive phosphor similar to Dy:YAG.
-doped YAG (Tb:YAG) is a phosphor used in cathode ray tubes. It emits at yellow-green color, at 544 nm.
(III)-doped YAG (Ce:YAG or YAG:Ce) is a phosphor, or a scintillator
when in pure single-crystal form, with wide range of uses. It emits yellow light when subjected to blue or ultraviolet light, or to x-ray light. It is used in white light-emitting diode
s, as a coating on a high-brightness blue InGaN diode, converting part of the blue light into yellow, which then appears 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 lamp
s 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 tube
s, 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 photomultiplier
s.
Ce:YAG is used in PET scanner
s, high-energy gamma radiation and charged particle
detectors, and high-resolution imaging screens for gamma, x-ray
s, beta radiation and ultraviolet radiation.
Ce:YAG can be further doped with gadolinium
.
Yttrium
Yttrium is a chemical element with symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and it has often been classified as a "rare earth element". Yttrium is almost always found combined with the lanthanides in rare earth minerals and is...
3Al
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
5O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
12) is a synthetic crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
line material of the garnet
Garnet
The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives. The name "garnet" may come from either the Middle English word gernet meaning 'dark red', or the Latin granatus , possibly a reference to the Punica granatum , a plant with red seeds...
group. It is also one of three phases of the yttria-aluminium composite, the other two being yttrium aluminium monoclinic (YAM) and yttrium aluminium perovskite (YAP). YAG is commonly used as a host material in various solid-state laser
Solid-state laser
A solid-state laser is a laser that uses a gain medium that is a solid, rather than a liquid such as in dye lasers or a gas as in gas lasers. Semiconductor-based lasers are also in the solid state, but are generally considered as a separate class from solid-state lasers .-Solid-state...
s. Rare earth elements such as neodymium
Neodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is a soft silvery metal that tarnishes in air. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite...
and erbium
Erbium
Erbium is a chemical element in the lanthanide series, with the symbol Er and atomic number 68. A silvery-white solid metal when artificially isolated, natural erbium is always found in chemical combination with other elements on Earth...
can be doped into YAG as active laser ions, yielding Nd:YAG
Nd:YAG laser
Nd:YAG is a crystal that is used as a lasing medium for solid-state lasers. The dopant, triply ionized neodymium, typically replaces yttrium in the crystal structure of the yttrium aluminium garnet , since they are of similar size...
and Er:YAG
Er:YAG laser
Er:YAG lasers are solid-state lasers whose lasing medium is erbium-doped yttrium aluminium garnet . Er:YAG lasers typically emit light with a wavelength of 2940 nm, which is infrared light. Unlike Nd:YAG lasers, the output of an Er:YAG laser is strongly absorbed by water because of atomic resonances...
lasers, respectively. Cerium
Cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight...
-doped YAG (YAG:Ce) is used as a phosphor
Phosphor
A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
in cathode ray tube
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
s and white light-emitting diode
Light-emitting diode
A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...
s, and as a scintillator
Scintillator
A scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...
.
Gemstone YAG
YAG for a period was used in jewelry as a diamondDiamond simulant
The high price of gem-grade diamonds, as well as significant ethical concerns of the diamond trade, have created a large demand for materials with similar gemological characteristics, known as diamond simulants or imitations. Simulants are distinct from synthetic diamond, which unlike simulants is...
and other gemstone
Gemstone
A gemstone or gem is a piece of mineral, which, in cut and polished form, is used to make jewelry or other adornments...
simulant. Colored variants and their doping elements include: green (chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
), blue (cobalt
Cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
), red (manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
), yellow (titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
), purple (neodymium
Neodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is a soft silvery metal that tarnishes in air. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite...
), pink, and orange. As faceted gems they are valued (as synthetics) for their clarity, durability, high refractive index
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
and dispersion
Dispersion (optics)
In optics, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency, or alternatively when the group velocity depends on the frequency.Media having such a property are termed dispersive media...
. The critical angle
Critical angle
Critical angle can refer to:*Critical angle the angle of incidence above which total internal reflection occurs*Critical angle of attack, in aerodynamics; the angle of attack which produces the maximum lift coefficient...
of YAG is 33 degrees. YAG cuts similar to natural garnet
Garnet
The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives. The name "garnet" may come from either the Middle English word gernet meaning 'dark red', or the Latin granatus , possibly a reference to the Punica granatum , a plant with red seeds...
, with polishing being performed with alumina or diamond
Diamond
In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...
(50,000 or 100,000) 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
Cubic zirconia
Cubic zirconia is the cubic crystalline form of zirconium dioxide . The synthesized material is hard, optically flawless and usually colorless, but may be made in a variety of different colors. It should not be confused with zircon, which is a zirconium silicate...
; 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.
Nd:YAG
NeodymiumNeodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is a soft silvery metal that tarnishes in air. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite...
-doped
Dopant
A dopant, also called a doping agent, is a trace impurity element that is inserted into a substance in order to alter the electrical properties or the optical properties of the substance. In the case of crystalline substances, the atoms of the dopant very commonly take the place of elements that...
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
Active laser medium
The active laser medium is the source of optical gain within a laser. The gain results from the stimulated emission of electronic or molecular transitions to a lower energy state from a higher energy state...
in solid-state laser
Solid-state laser
A solid-state laser is a laser that uses a gain medium that is a solid, rather than a liquid such as in dye lasers or a gas as in gas lasers. Semiconductor-based lasers are also in the solid state, but are generally considered as a separate class from solid-state lasers .-Solid-state...
s, being used for everything from low-power continuous-wave lasers to high-power Q-switched
Q-switching
Q-switching, sometimes known as giant pulse formation, is a technique by which a laser can be made to produce a pulsed output beam. The technique allows the production of light pulses with extremely high peak power, much higher than would be produced by the same laser if it were operating in a...
(pulsed) lasers with power levels measured in the kilowatts. The thermal conductivity of Nd:YAG is higher and its fluorescence
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
lifetime is about twice as long as that of Nd:YVO4
Neodymium doped yttrium orthovanadate
Neodymium-doped yttrium orthovanadate is a crystalline material formed by adding neodymium ions to yttrium orthovanadate. It is commonly used as an active laser medium for diode-pumped solid-state lasers. It comes as a transparent blue-tinted material...
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
Laser pumping
Laser pumping is the act of energy transfer from an external source into the gain medium of a laser. The energy is absorbed in the medium, producing excited states in its atoms. When the number of particles in one excited state exceeds the number of particles in the ground state or a less-excited...
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
Lens (anatomy)
The crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a...
onto the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
, 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 crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
s, to produce green light with a wavelength of 532 nm or ultraviolet light at 355 nm, respectively.
The dopant
Dopant
A dopant, also called a doping agent, is a trace impurity element that is inserted into a substance in order to alter the electrical properties or the optical properties of the substance. In the case of crystalline substances, the atoms of the dopant very commonly take the place of elements that...
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 neodymiumNeodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is a soft silvery metal that tarnishes in air. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite...
and chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
(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 laser
Solar-pumped laser
A solar-pumped laser, is a laser that shares the same optical properties as conventional lasers such as emitting a beam consisting of coherent electromagnetic radiation which can reach high power, but which uses solar radiation for pumping the lasing medium...
s, which could form part of a solar power satellite system.
Er:YAG
ErbiumErbium
Erbium is a chemical element in the lanthanide series, with the symbol Er and atomic number 68. A silvery-white solid metal when artificially isolated, natural erbium is always found in chemical combination with other elements on Earth...
-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
Tooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...
and in cosmetic surgery. Er:YAG is used for noninvasive monitoring of blood sugar
Blood sugar
The blood sugar concentration or blood glucose level is the amount of glucose present in the blood of a human or animal. Normally in mammals, the body maintains the blood glucose level at a reference range between about 3.6 and 5.8 mM , or 64.8 and 104.4 mg/dL...
. 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
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
), works well at room temperature, and has high slope efficiency
Slope efficiency
The slope efficiency is an important property of a laser. It is obtained by plotting the laser output power against the input pump power. Above the lasing threshold, the resulting curve is usually close to a straight line. The slope efficiency is the slope of this line. Slope efficiency can...
. Er:YAG is pale green.
Yb:YAG
YtterbiumYtterbium
Ytterbium is a chemical element with the symbol Yb and atomic number 70. A soft silvery metallic element, ytterbium is a rare earth element of the lanthanide series and is found in the minerals gadolinite, monazite, and xenotime. The element is sometimes associated with yttrium or other related...
-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 0.2-30% of replaced yttrium atoms. Yb:YAG has very low fractional heating, very high slope efficiency
Slope efficiency
The slope efficiency is an important property of a laser. It is obtained by plotting the laser output power against the input pump power. Above the lasing threshold, the resulting curve is usually close to a straight line. The slope efficiency is the slope of this line. Slope efficiency can...
, and no excited-state absorption or up-conversion, high mechanical strength and high thermal conductivity. Yb:YAG can be pumped by reliable InGaAs laser diode
Laser diode
The laser diode is a laser where the active medium is a semiconductor similar to that found in a light-emitting diode. The most common type of laser diode is formed from a p-n junction and powered by injected electric current...
s 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
NeodymiumNeodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is a soft silvery metal that tarnishes in air. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite...
-cerium
Cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight...
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
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
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
Lasing threshold
The lasing threshold is the lowest excitation level at which a laser's output is dominated by stimulated emission rather than by spontaneous emission. Below the threshold, the laser's output power rises slowly with increasing excitation. Above threshold, the slope of power vs. excitation is orders...
. Usually 1.1-1.4 % of Y atoms are replaced with Nd, and 0.05-0.1% with Ce.
Ho:Cr:Tm:YAG
HolmiumHolmium
Holmium is a chemical element with the symbol Ho and atomic number 67. Part of the lanthanide series, holmium is a rare earth element. Its oxide was first isolated from rare earth ores in 1878 and the element was named after the city of Stockholm....
-chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
-thulium
Thulium
Thulium is a chemical element that has the symbol Tm and atomic number 69. Thulium is the second least abundant of the lanthanides . It is an easily workable metal with a bright silvery-gray luster...
triple-doped YAG (Ho:Cr:Tm:YAG, or Ho,Cr,Tm:YAG) is an active laser medium material with high efficiency. It lases at 2097 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
Slope efficiency
The slope efficiency is an important property of a laser. It is obtained by plotting the laser output power against the input pump power. Above the lasing threshold, the resulting curve is usually close to a straight line. The slope efficiency is the slope of this line. Slope efficiency can...
, and operates at a wavelength where the threshold for eye damage is relatively high. When pumped by a diode, the 781 nm band is used. Other major pump bands are located between 400 and 800 nm. The dopant levels used are 0.35 atom.% Ho, 5.8 atom.% Tm, and 1.5 at.% Cr. The rods have green color, imparted by chromium(III).
Tm:YAG
ThuliumThulium
Thulium is a chemical element that has the symbol Tm and atomic number 69. Thulium is the second least abundant of the lanthanides . It is an easily workable metal with a bright silvery-gray luster...
-doped YAG (Tm:YAG) is an active laser medium that operates between 1930 and 2040 nm. It is suitable for diode pumping. A dual-mode Tm:YAG laser emits two frequencies separated by 1 GHz.
Cr4+:YAG
ChromiumChromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
(IV)-doped YAG (Cr:YAG) provides a large absorption cross section in the 0.9-1.2 micrometer spectral region, which makes it an attractive choice as a passive Q-switch for Nd-doped lasers. The resulting devices are solid-state, compact and low-cost. Cr:YAG has high damage threshold, good thermal conductivity, good chemical stability, resists ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
radiation, and is easily machinable. It is replacing more traditional Q-switching materials like lithium fluoride
Lithium fluoride
Lithium fluoride is an inorganic compound with the formula LiF. It is the lithium salt of hydrofluoric acid. This white solid is a simple ionic compound. Its structure is analogous to that of sodium chloride, but it is much less soluble in water. It is mainly used as a component of molten...
and organic dye
Dye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....
s. 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
Neodymium doped yttrium orthovanadate
Neodymium-doped yttrium orthovanadate is a crystalline material formed by adding neodymium ions to yttrium orthovanadate. It is commonly used as an active laser medium for diode-pumped solid-state lasers. It comes as a transparent blue-tinted material...
, and Yb:YAG.
Cr:YAG can be also used as a laser gain medium itself, producing tunable laser
Tunable laser
A tunable laser is a laser whose wavelength of operation can be altered in a controlled manner. While all laser gain media allow small shifts in output wavelength, only a few types of lasers allow continuous tuning over a significant wavelength range....
s with outputs adjustable between 1350 and 1550 nm. The Cr:YAG laser can generate ultrashort pulse
Ultrashort pulse
In optics, an ultrashort pulse of light is an electromagnetic pulse whose time duration is of the order of a femtosecond . Such pulses have a broadband optical spectrum, and can be created by mode-locked oscillators...
s (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
DysprosiumDysprosium
Dysprosium is a chemical element with the symbol Dy and atomic number 66. It is a rare earth element with a metallic silver luster. Dysprosium is never found in nature as a free element, though it is found in various minerals, such as xenotime...
-doped YAG (Dy:YAG) is a temperature-sensitive phosphor
Phosphor
A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
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
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
. The phosphor can be applied directly to the measured surface, or to an end of an optical fiber
Optical fiber
An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...
.
Sm:YAG
SamariumSamarium
Samarium is a chemical element with the symbol Sm, atomic number 62 and atomic weight 150.36. It is a moderately hard silvery metal which readily oxidizes in air. Being a typical member of the lanthanide series, samarium usually assumes the oxidation state +3...
-doped YAG (Sm:YAG) is a temperature-sensitive phosphor similar to Dy:YAG.
Tb:YAG
TerbiumTerbium
Terbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white rare earth metal that is malleable, ductile and soft enough to be cut with a knife...
-doped YAG (Tb:YAG) is a phosphor used in cathode ray tubes. It emits at yellow-green color, at 544 nm.
Ce:YAG
CeriumCerium
Cerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight...
(III)-doped YAG (Ce:YAG or YAG:Ce) is a phosphor, or a scintillator
Scintillator
A scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...
when in pure single-crystal form, with wide range of uses. It emits yellow light when subjected to blue or ultraviolet light, or to x-ray light. It is used in white light-emitting diode
Light-emitting diode
A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...
s, as a coating on a high-brightness blue InGaN diode, converting part of the blue light into yellow, which then appears 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 lamp
Mercury-vapor lamp
A mercury-vapor lamp is a gas discharge lamp that uses an electric arc through vaporized mercury to produce light. The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger borosilicate glass bulb...
s 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 tube
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
s, 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 photomultiplier
Photomultiplier
Photomultiplier tubes , members of the class of vacuum tubes, and more specifically phototubes, are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum...
s.
Ce:YAG is used in PET scanner
Positron emission tomography
Positron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
s, high-energy gamma radiation and charged particle
Charged particle
In physics, a charged particle is a particle with an electric charge. It may be either a subatomic particle or an ion. A collection of charged particles, or even a gas containing a proportion of charged particles, is called a plasma, which is called the fourth state of matter because its...
detectors, and high-resolution imaging screens for gamma, x-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s, beta radiation and ultraviolet radiation.
Ce:YAG can be further doped with gadolinium
Gadolinium
Gadolinium is a chemical element with the symbol Gd and atomic number 64. It is a silvery-white, malleable and ductile rare-earth metal. It is found in nature only in combined form. Gadolinium was first detected spectroscopically in 1880 by de Marignac who separated its oxide and is credited with...
.
See also
- Yttrium iron garnetYttrium iron garnetYttrium iron garnet is a kind of synthetic garnet, with chemical composition 323, or Y3Fe5O12. It is a ferrimagnetic material with a Curie temperature of 550 K....
- Gadolinium gallium garnetGadolinium gallium garnetGadolinium Gallium Garnet is a synthetic crystalline material of the garnet group, with good mechanical, thermal, and optical properties. It is typically colorless. It has cubic lattice, density 7.08 g/cm³ and Mohs hardness is variously noted as 6.5 and 7.5...
- Micro-Pulling-DownMicro-pulling-down-Basics:The micro-pulling-down method is a crystal growth technique based on continuous transport of the melted substance through micro-channel made in a crucible bottom. Continuous solidification of the melt is progressed on a liquid/solid interface positioned under the crucible...
- Nd:YAG laserNd:YAG laserNd:YAG is a crystal that is used as a lasing medium for solid-state lasers. The dopant, triply ionized neodymium, typically replaces yttrium in the crystal structure of the yttrium aluminium garnet , since they are of similar size...
- Er:YAG laserEr:YAG laserEr:YAG lasers are solid-state lasers whose lasing medium is erbium-doped yttrium aluminium garnet . Er:YAG lasers typically emit light with a wavelength of 2940 nm, which is infrared light. Unlike Nd:YAG lasers, the output of an Er:YAG laser is strongly absorbed by water because of atomic resonances...