Nd:YAG (neodymium-doped yttrium aluminum garnet; Nd:Y₃Al₅O₁₂) is a

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macr ...

that is used as a lasing medium for

solid-state laser A solid-state laser is a laser that uses a gain medium that is a solid, rather than a liquid 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 ...

s. The

dopant A dopant, also called a doping agent, is a trace of impurity element that is introduced into a chemical material to alter its original electrical or optical properties. The amount of dopant necessary to cause changes is typically very low. Wh ...

, triply ionized

neodymium Neodymium is a chemical element with the symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishes ...

, Nd(III), typically replaces a small fraction (1%) of the

yttrium Yttrium is a chemical element with the symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a " rare-earth element". Yttrium is almost always found in c ...

ions in the host crystal structure of the yttrium aluminum garnet (YAG), since the two ions are of similar size.Koechner §2.3, pp. 48–53. It is the neodymium ion which provides the lasing activity in the crystal, in the same fashion as red chromium ion in ruby lasers. Laser operation of Nd:YAG was first demonstrated by J.E. Geusic ''et al.'' at

Bell Laboratories Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company owned by mul ...

in 1964.

Technology

Nd: YAG lasers are optically pumped using a

flashtube A flashtube (flashlamp) is an electric arc lamp designed to produce extremely intense, Coherence (physics), incoherent, full-spectrum white light for a very short time. A flashtube is a glass tube with an electrode at each end and is filled with ...

laser diode The laser diode chip removed and placed on the eye of a needle for scale A laser diode (LD, also injection laser diode or ILD, or diode laser) is a semiconductor device similar to a light-emitting diode in which a diode pumped directly with e ...

s. These are one of the most common types of laser, and are used for many different applications. Nd:YAG lasers typically emit light with a

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tr ...

of 1064 nm, in the

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from aroun ...

. However, there are also transitions near 946, 1120, 1320, and 1440 nm. Nd:YAG lasers operate in both pulsed and continuous mode. Pulsed Nd:YAG lasers are typically operated in the so-called Q-switching mode: An optical switch is inserted in the laser cavity waiting for a maximum population inversion in the neodymium ions before it opens. Then the light wave can run through the cavity, depopulating the excited laser medium at maximum population inversion. In this Q-switched mode, output powers of 250 megawatts and pulse durations of 10 to 25 nanoseconds have been achieved. The high-intensity pulses may be efficiently frequency doubled to generate laser light at 532 nm, or higher harmonics at 355, 266 and 213 nm. Nd:YAG absorbs mostly in the bands between 730–760 nm and 790–820 nm. At low current densities

krypton Krypton (from grc, κρυπτός, translit=kryptos 'the hidden one') is a chemical element with the symbol Kr and atomic number 36. It is a colorless, odorless, tasteless noble gas that occurs in trace amounts in the atmosphere and is often ...

flashlamps have higher output in those bands than do the more common

xenon Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...

lamps, which produce more light at around 900 nm. The former are therefore more efficient for pumping Nd:YAG lasers.Koechner §6.1.1, pp. 251–64. The amount of the neodymium

in the material varies according to its use. For continuous wave output, the doping is significantly lower than for pulsed lasers. The lightly doped CW rods can be optically distinguished by being less colored, almost white, while higher-doped rods are pink-purplish. Other common host materials for neodymium are: YLF ( yttrium lithium fluoride, 1047 and 1053 nm), YVO₄ (

yttrium orthovanadate Yttrium orthovanadate (YVO4) is a transparent crystal. Undoped YVO4 is also used to make efficient high-power polarizing prisms similar to Glan–Taylor prisms. There are two principal applications for doped Yttrium orthovanadate: *Doped with n ...

, 1064 nm), and

glass Glass is a non-Crystallinity, crystalline, often transparency and translucency, transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most ...

. A particular host material is chosen in order to obtain a desired combination of optical, mechanical, and thermal properties. Nd:YAG lasers and variants are pumped either by

s, continuous gas discharge lamps, or near-infrared

s ( DPSS lasers). Prestabilized laser (PSL) types of Nd:YAG lasers have proved to be particularly useful in providing the main beams for

gravitational wave Gravitational waves are waves of the intensity of gravity generated by the accelerated masses of an orbital binary system that propagate as waves outward from their source at the speed of light. They were first proposed by Oliver Heaviside in ...

interferometer Interferometry is a technique which uses the '' interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber o ...

s such as

LIGO The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. Two large o ...

VIRGO Virgo may refer to: * Virgo (astrology), the sixth astrological sign of the zodiac * Virgo (constellation), a constellation * Virgo Cluster, a cluster of galaxies in the constellation Virgo * Virgo Stellar Stream, remains of a dwarf galaxy *Virgo ...

GEO600 GEO600 is a gravitational wave detector located near Sarstedt, a town 20 km to the south of Hanover, Germany. It is designed and operated by scientists from the Max Planck Institute for Gravitational Physics, Max Planck Institute of Quantum Opti ...

and TAMA.

Applications

Medicine

Nd:YAG lasers are used in

ophthalmology Ophthalmology ( ) is a surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a med ...

to correct

posterior capsular opacification Cataract surgery, also called lens replacement surgery, is the removal of the natural lens of the eye (also called "crystalline lens") that has developed an opacification, which is referred to as a cataract, and its replacement with an intrao ...

, after

cataract A cataract is a cloudy area in the lens of the eye that leads to a decrease in vision. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry or double vision, halos around light, trouble w ...

surgery, for peripheral

iridotomy An iridectomy, also known as a surgical iridectomy or corectomy, is the surgical removal of part of the iris.Cline D; Hofstetter HW; Griffin JR. ''Dictionary of Visual Science''. 4th ed. Butterworth-Heinemann, Boston 1997. chronic and acute angle-closure glaucoma, where it has largely superseded surgical iridectomy, for the treatment of vitreous eye floaters, for pan-retinal photocoagulation in the treatment of proliferative diabetic retinopathy, and to damage the

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...

in ophthalmology animal research. Nd:YAG lasers emitting light at 1064 nm have been the most widely used laser for laser-induced thermotherapy, in which benign or malignant lesions in various organs are ablated by the beam. In

oncology Oncology is a branch of medicine that deals with the study, treatment, diagnosis and prevention of cancer. A medical professional who practices oncology is an ''oncologist''. The name's etymological origin is the Greek word ὄγκος (''ó ...

, Nd:YAG lasers can be used to remove skin

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bl ...

s. They are also used to reduce benign thyroid nodules, and to destroy primary and secondary malignant liver lesions. To treat

benign prostatic hyperplasia Benign prostatic hyperplasia (BPH), also called prostate enlargement, is a noncancerous increase in size of the prostate gland. Symptoms may include frequent urination, trouble starting to urinate, weak stream, inability to urinate, or loss ...

(BPH), Nd:YAG lasers can be used for laser prostate surgery—a form of

transurethral resection of the prostate Transurethral resection of the prostate (commonly known as a TURP, plural TURPs, and rarely as a transurethral prostatic resection, TUPR) is a urological operation. It is used to treat benign prostatic hyperplasia (BPH). As the name indicates, ...

. These lasers are also used extensively in the field of cosmetic medicine for laser hair removal and the treatment of minor

vascular Blood vessels are the structures of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away from ...

defects such as spider veins on the face and legs. Nd:YAG lasers are also used to treat venous lake lip lesions. Recently Nd:YAG lasers have been used for treating

dissecting cellulitis of the scalp Dissecting cellulitis of the scalp, also known as dissecting folliculitis, perifolliculitis capitis abscedens et suffodiens of Hoffman, perifolliculitis abscedens et suffodiens, or folliculitis abscedens et suffodiens, is an inflammatory condition ...

, a rare skin disease. Using

hysteroscopy Hysteroscopy is the inspection of the uterine cavity by endoscopy with access through the cervix. It allows for the diagnosis of intrauterine pathology and serves as a method for surgical intervention (operative hysteroscopy). Hysteroscope A hyst ...

the Nd:YAG laser has been used for removal of uterine septa within the inside of the uterus. In

podiatry Podiatry () or podiatric medicine () is a branch of medicine devoted to the study, diagnosis, medical and surgical treatment of disorders of the foot, ankle, and leg. A Doctor of Podiatric Medicine (DPM), or a podiatrist, is a healthcare ...

, the Nd:YAG laser is being used to treat

onychomycosis Onychomycosis, also known as tinea unguium, is a fungal infection of the nail. Symptoms may include white or yellow nail discoloration, thickening of the nail, and separation of the nail from the nail bed. Toenails or fingernails may be affec ...

, which is fungus infection of the toenail. The merits of laser treatment of these infections are not yet clear, and research is being done to establish effectiveness.

Dentistry

Nd:YAG dental lasers have been used for the removal of

dental caries Tooth decay, also known as cavities or caries, is the breakdown of teeth due to acids produced by bacteria. The cavities may be a number of different colors from yellow to black. Symptoms may include pain and difficulty with eating. Complicatio ...

as an alternative to drill therapy, although evidence supporting its use is of low quality. They have also been used for

soft tissue Soft tissue is all the tissue in the body that is not hardened by the processes of ossification or calcification such as bones and teeth. Soft tissue connects, surrounds or supports internal organs and bones, and includes muscle, tendons, liga ...

surgeries Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical specialty that uses operative manual and instrumental techniques on a person to investigate or treat a pat ...

in the

oral cavity In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on t ...

, such as gingivectomy, periodontal sulcular debridement,

LANAP Laser-assisted new attachment procedure (LANAP) is a surgical therapy for the treatment of periodontitis, intended to work through regeneration rather than resection. This therapy and the laser used to perform it have been in use since 1994. It ...

, and pulpotomy. Nd:YAG dental lasers have also been shown to be effective at treating and preventing dental hypersensitivity, as an

adjunct Adjunct may refer to: * Adjunct (grammar), words used as modifiers * Adjunct professor, a rank of university professor * Adjuncts, sources of sugar used in brewing * Adjunct therapy used to complement another main therapeutic agent, either to impr ...

for periodontal instrumentation, and for the treatment of recurrent

aphthous stomatitis Aphthous stomatitis, or recurrent aphthous stomatitis (RAS), is a common condition characterized by the repeated formation of benign and non- contagious mouth ulcers (aphthae) in otherwise healthy individuals. The informal term ''canker sore'' ...

Manufacturing

Nd:YAG lasers are used in manufacturing for engraving, etching, or marking a variety of metals and plastics, or for metal surface enhancement processes like laser peening. They are extensively used in manufacturing for

cutting Cutting is the separation or opening of a physical object, into two or more portions, through the application of an acutely directed force. Implements commonly used for cutting are the knife and saw, or in medicine and science the scalpel and ...

and welding steel,

semiconductors A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

and various alloys. For automotive applications (cutting and welding steel) the power levels are typically 1–5 kW. Super alloy drilling (for gas turbine parts) typically uses pulsed Nd:YAG lasers (millisecond pulses, not Q-switched). Nd:YAG lasers are also employed to make

subsurface marking In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of b ...

s in transparent materials such as

acrylic glass Poly(methyl methacrylate) (PMMA) belongs to a group of materials called engineering plastics. It is a transparent thermoplastic. PMMA is also known as acrylic, acrylic glass, as well as by the trade names and brands Crylux, Plexiglas, Acrylit ...

. Lasers of up to 2 kW are used for selective laser melting of metals in additive layered manufacturing. In aerospace applications, they can be used to

drill A drill is a tool used for making round holes or driving fasteners. It is fitted with a bit, either a drill or driver chuck. Hand-operated types are dramatically decreasing in popularity and cordless battery-powered ones proliferating due to ...

cooling holes for enhanced air flow/heat exhaust efficiency. Nd:YAG lasers are also used in the non-conventional rapid prototyping process laser engineered net shaping (LENS). Laser peening typically uses a high energy (10 to 40 joule) 10 to 30 nanosecond pulse. The laser beam is focused down to a few millimeters in diameter to deposit gigawatts of power on the surface of a part. Laser peening is unlike other manufacturing processes in that it neither heats or adds material; it is a mechanical process of

cold working In metallurgy, cold forming or cold working is any metalworking process in which metal is shaped below its recrystallization temperature, usually at the ambient temperature. Such processes are contrasted with hot working techniques like hot ro ...

the metallic component to impart compressive residual stresses. Laser peening is widely used in gas-fired turbine engines in both aerospace and power generation to increase strength and improve resistance to damage and

metal fatigue In materials science, fatigue is the initiation and propagation of cracks in a material due to cyclic loading. Once a fatigue crack has initiated, it grows a small amount with each loading cycle, typically producing striations on some parts o ...

Fluid dynamics

Nd:YAG lasers can be used for flow visualization techniques in fluid dynamics (for example particle image velocimetry or

laser-induced fluorescence Laser-induced fluorescence (LIF) or laser-stimulated fluorescence (LSF) is a spectroscopic method in which an atom or molecule is excited to a higher energy level by the absorption of laser light followed by spontaneous emission of light. It was ...

Biophysics

Nd:YAG lasers are frequently used to build

optical tweezers Optical tweezers (originally called single-beam gradient force trap) are scientific instruments that use a highly focused laser beam to hold and move microscopic and sub-microscopic objects like atoms, nanoparticles and droplets, in a manner simila ...

for biological applications. This is because Nd:YAG lasers mostly emit at a wavelength of 1064 nm. Biological samples have a low absorption coefficient at this wavelength, as biological samples are usually mostly made up of water. As such, using an Nd:YAG laser minimizes the damage to the biological sample being studied.

Automotive

Researchers from Japan's National Institutes of Natural Sciences are developing laser igniters that use YAG chips to ignite fuel in an engine, in place of a

spark plug A spark plug (sometimes, in British English, a sparking plug, and, colloquially, a plug) is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air ...

. The lasers use several 800 picosecond long pulses to ignite the fuel, producing faster and more uniform ignition. The researchers say that such igniters could yield better performance and fuel economy, with fewer harmful emissions.

Military

The Nd:YAG laser is the most common laser used in

laser designator A laser designator is a laser light source which is used to designate a target. Laser designators provide targeting for laser-guided bombs, missiles, or precision artillery munitions, such as the Paveway series of bombs, AGM-114 Hellfire ...

s and

laser rangefinder A laser rangefinder, also known as a laser telemeter, is a rangefinder that uses a laser beam to determine the distance to an object. The most common form of laser rangefinder operates on the time of flight principle by sending a laser pulse in ...

s. During the

Iran–Iraq War The Iran–Iraq War was an armed conflict between Iran and Iraq that lasted from September 1980 to August 1988. It began with the Iraqi invasion of Iran and lasted for almost eight years, until the acceptance of United Nations Security Counci ...

, Iranian soldiers suffered more than 4000 cases of laser eye injury, caused by a variety of Iraqi sources including tank rangefinders. The 1064 nm wavelength of Nd:YAG is thought to be particularly dangerous, as it is invisible and initial exposure is painless. The Chinese ZM-87 blinding laser weapon uses a laser of this type, though only 22 have been produced due to their

prohibition Prohibition is the act or practice of forbidding something by law; more particularly the term refers to the banning of the manufacture, storage (whether in barrels or in bottles), transportation, sale, possession, and consumption of alcoholic ...

by the

Convention on Certain Conventional Weapons The United Nations Convention on Certain Conventional Weapons (CCW or CCWC), concluded at Geneva on October 10, 1980, and entered into force in December 1983, seeks to prohibit or restrict the use of certain conventional weapons which are consi ...

. North Korea is reported to have used one of these weapons against American helicopters in 2003.

Cavity ring-down spectroscopy (CRDS)

The Nd:YAG may be used in the application of cavity ring-down spectroscopy, which is used to measure the concentration of some light-absorbing substance.

Laser-induced breakdown spectroscopy (LIBS)

A range of Nd:YAG lasers are used in analysis of elements in the periodic table. Though the application by itself is fairly new with respect to conventional methods such as XRF or ICP, it has proven to be less time consuming and a cheaper option to test element concentrations. A high-power Nd:YAG laser is focused onto the sample surface to produce plasma. Light from the plasma is captured by spectrometers and the characteristic spectra of each element can be identified, allowing concentrations of elements in the sample to be measured.

Laser pumping

Nd:YAG lasers, mainly via their second and third harmonics, are widely used to excite

dye lasers A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and ...

either in the liquid or

solid state Solid state, or solid matter, is one of the four fundamental states of matter. Solid state may also refer to: Electronics * Solid-state electronics, circuits built of solid materials * Solid state ionics, study of ionic conductors and their u ...

. They are also used as pump sources for vibronically broadened solid-state lasers such as Cr⁴⁺:YAG or via the second harmonic for pumping Ti:sapphire lasers.

Additional frequencies

For many applications, the infrared light is frequency-doubled or -tripled using

nonlinear optical materials In mathematics and science, a nonlinear system is a system in which the change of the output is not proportional to the change of the input. Nonlinear problems are of interest to engineers, biologists, physicists, mathematicians, and many other ...

such as

lithium triborate Lithium triborate (LiB3O5) or LBO is a non-linear optics crystal. It has a wide transparency range, moderately high nonlinear coupling, high damage threshold and desirable chemical and mechanical properties. This crystal is often used for secon ...

to obtain visible (532 nm, green) or

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiati ...

light.

Cesium lithium borate Caesium lithium borate or cesium lithium borate (CsLiB6O10), also known as CLBO, is a Nonlinear optics, non-linear crystal for ultraviolet applications and generates the fourth and fifth harmonics of the Nd:YAG Fundamental frequency, fundamental la ...

generates the 4th and 5th harmonics of the Nd:YAG 1064 nm fundamental wavelength. A green laser pointer is a frequency doubled Nd:YVO₄ diode-pumped solid state laser ( DPSS laser). Nd:YAG can be also made to lase at its non-principal wavelength. The line at 946 nm is typically employed in "blue laser pointer" DPSS lasers, where it is doubled to 473 nm.

Physical and chemical properties of Nd:YAG

Properties of YAG crystal

* Formula: Y₃Al₅O₁₂ * Molecular weight: 596.7 * Crystal structure: Cubic * Hardness: 8–8.5 (Mohs) * Melting point: 1970 °C (3540 °F) * Density: 4.55 g/cm³

Refractive index of Nd:YAG

Properties of Nd:YAG @ 25 °C (with 1% Nd doping)

* Formula: Y_2.97Nd_0.03Al₅O₁₂ * Weight of Nd: 0.725% * Atoms of Nd per unit volume: 1.38×10²⁰ /cm³ * Charge state of Nd: 3⁺ * Emission wavelength: 1064 nm * Transition: ⁴F_3/2 → ⁴I_11/2 * Duration of fluorescence: 230 μs * Thermal conductivity: 0.14 W·cm⁻¹·K⁻¹ * Specific heat capacity: 0.59 J·g⁻¹·K⁻¹ * Thermal expansion: 6.9×10⁻⁶ K⁻¹ * d''n''/d''T'': 7.3×10⁻⁶ K⁻¹ * Young's modulus: 3.17×10⁴ K·g/mm⁻² * Poisson's ratio: 0.25 * Resistance to thermal shock: 790 W·m⁻¹

References and notes

* * {{Solid-state laser Solid-state lasers Dental lasers Ophthalmology Laser medicine Medical equipment Neodymium compounds Yttrium compounds Aluminium compounds