Blue laser
Encyclopedia
A so-called blue laser is a laser
that emits electromagnetic radiation
at a wavelength
of between 360 and 480 nanometre
s, which the human eye sees as blue or violet. Diode lasers which emit light at 445 nm are becoming popular as handheld lasers. Light of a shorter wavelength than 400 nm is classified as ultraviolet. Lasers emitting wavelengths below 445 nm appear violet
to the human eye, a distinctly different color. This is true, for example; of the most commercially-common "blue" lasers, the diode lasers used in Blu-ray
applications, which emit 405 nm violet light, which is a short enough wavelength to cause fluorescence
in some chemicals, in the same way as radiation further into the ultraviolet ("black light
") does.
The class of blue lasers are frequently semiconductor laser diode
s based on gallium(III) nitride
(GaN; violet color) or indium gallium nitride
(often true blue in color, but also able to produce other colors). Both blue and violet lasers can also be constructed using frequency-doubling of infrared laser wavelengths from diode lasers or diode-pumped lasers.
Devices that employ blue laser light have applications in many areas ranging from optoelectronic data storage at high density to medical applications.
s can be built on gallium arsenide (GaAs) semiconductors, upon which a dozen layers of atoms are placed to form the part of the laser that generates light from quantum well
s. Using methods similar to those developed for silicon, the substrate can be built free of the defects called dislocation
s, and the atoms laid down so the distance between the ones making up the ground and those of the quantum well
s are the same.
But the best semiconductor for blue lasers is gallium nitride (GaN) crystals, which are much harder to manufacture, requiring higher pressures and temperatures, similar to the ones that produce synthetic diamonds, and the use of high-pressure nitrogen gas. The technical problems seemed insurmountable, so researchers since the 1960s have sought to deposit GaN on a base of readily available sapphire
. But a mismatch between the structures of sapphire and gallium nitride created too many defects.
In 1992 Japanese inventor Shuji Nakamura
invented the first efficient blue LED, and four years later, the first blue laser. Nakamura used the material deposited on the sapphire substrate, although the number of defects remained too high (106–1010/cm2) to easily build a high-power laser.
In the early 1990s the Institute of High Pressure Physics at the Polish Academy of Sciences in Warsaw (Poland
), under the leadership of Dr. Sylwester Porowski
developed technology to create gallium nitride crystals with high structural quality and fewer than 100 defects per square centimeter — at least 10,000 times better than the best sapphire-supported crystal.
In 1999, Nakamura tried Polish crystals, producing lasers with twice the yield and ten times the lifetime — 3,000 hours at 30 mW.
A further development of the technology has led to mass production of the device. Today, blue lasers use a sapphire surface covered with a layer of gallium nitride (this technology is used by Japanese company Nichia, which has an agreement with Sony
), and blue semiconductor lasers use a gallium nitride mono-crystal surface (Polish company TopGaN ).
After 10 years, Japanese manufacturers mastered the production of a blue laser with 60 mW of power, making them applicable for devices that read a dense high-speed stream of data from Blu-ray, BD-R, and BD-RE. Polish technology is cheaper than Japanese but has a smaller share of the market. There is one more Polish high-tech company which creates gallium nitride crystal – Ammono, but this company does not produce blue lasers.
For his work, Nakamura received the Millennium Technology Prize awarded in 2006.
Until the late 1990s, when blue semiconductor lasers were developed, blue lasers were large and expensive gas laser
instruments which relied on population inversion
in rare gas mixtures and needed high currents and strong cooling.
Thanks to prior development of many groups, including, most notably, Professor Isamu Akasaki
's group, Shuji Nakamura
at Nichia Corporation
and Sony Corporation in Anan (Tokushima-ken, Japan) made a series of inventions and developed commercially viable blue and violet semiconductor lasers. The active layer of the Nichia devices was formed from InGaN
quantum well
s or quantum dot
s spontaneously formed via self-assembly
. The new invention enabled the development of small, convenient and low-priced blue, violet, and ultraviolet UV lasers, which had not been available before, and opened the way for applications such as high-density HD DVD
data storage and Blu-ray discs. The shorter wavelength allows it to read discs containing much more information.
crystals are used as frequency doublers; for lower powers, KTP
is used. Output powers available are up to 1000 mW, but this usually is the total output including the infrared. As with green DPSS lasers, use of a 1000 mW IR diode usually results in approximately 300 mW of visible blue light, even if the laser is reported at 1000 mW power.
Blue lasers can also be fabricated directly with InGaN semiconductors, which produce blue light without frequency-doubling. 445 nm blue laser diodes are currently available on the open market. The devices are brighter than the 405 nm laser diodes, since the longer wavelength is closer to the peak sensitivity of the human eye. Commercial devices like laser projectors
have driven down the prices on these diodes, as of March 2011.
Violet lasers may be constructed directly with GaN (gallium nitride) semiconductors, as noted. However, a few higher-powered (120 mW) 404–405 nm "violet" laser pointers have become available which are not based on GaN, but also use DPSS frequency-doubler technology starting from 1 watt 808 nm gallium arsenide infrared diode lasers being directly doubled, without a longer-wave neodymium laser interposed between diode laser and doubler-crystal. As with all high powered lasers, such devices are able to pop balloons and light matches.
from brightening dyes.
For display applications which must appear "true blue", a wavelength of 450–460 nm is required. With advances in production, and commercial sales of low-cost laser projectors, 445 nm InGaN
laser diodes have dropped in price.
A last challenge in projection laser diodes is related to the construction of a "true green" InGaN laser (around 530 nm). Many companies have demonstrated devices working at only slightly shorter wavelengths: 480–500 nm.
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
that emits electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
at a wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
of between 360 and 480 nanometre
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...
s, which the human eye sees as blue or violet. Diode lasers which emit light at 445 nm are becoming popular as handheld lasers. Light of a shorter wavelength than 400 nm is classified as ultraviolet. Lasers emitting wavelengths below 445 nm appear violet
Violet (color)
As the name of a color, violet is synonymous with a bluish purple, when the word "purple" is used in the common English language sense of any color between blue and red, not including either blue or red...
to the human eye, a distinctly different color. This is true, for example; of the most commercially-common "blue" lasers, the diode lasers used in Blu-ray
Blu-ray Disc
Blu-ray Disc is an optical disc storage medium designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB per layer, with dual layer discs being the norm for feature-length video discs...
applications, which emit 405 nm violet light, which is a short enough wavelength to cause 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...
in some chemicals, in the same way as radiation further into the ultraviolet ("black light
Black light
A black light, also referred to as a UV light, ultraviolet light, or Wood's lamp, is a lamp that emits ultraviolet radiation in the long-wave range, and little visible light...
") does.
The class of blue lasers are frequently semiconductor 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 based on gallium(III) nitride
Gallium(III) nitride
Gallium nitride is a binary III/V direct bandgap semiconductor commonly used in bright light-emitting diodes since the 1990s. The compound is a very hard material that has a Wurtzite crystal structure. Its wide band gap of 3.4 eV affords it special properties for applications in optoelectronic,...
(GaN; violet color) or indium gallium nitride
Indium gallium nitride
Indium gallium nitride is a semiconductor material made of a mix of gallium nitride and indium nitride . It is a ternary group III/group V direct bandgap semiconductor. Its bandgap can be tuned by varying the amount of indium in the alloy...
(often true blue in color, but also able to produce other colors). Both blue and violet lasers can also be constructed using frequency-doubling of infrared laser wavelengths from diode lasers or diode-pumped lasers.
Devices that employ blue laser light have applications in many areas ranging from optoelectronic data storage at high density to medical applications.
Inventing blue-laser technology
Red laserHelium-neon laser
A helium–neon laser or HeNe laser, is a type of gas laser whose gain medium consists of a mixture of helium and neon inside of a small bore capillary tube, usually excited by a DC electrical discharge.- History of HeNe laser development:...
s can be built on gallium arsenide (GaAs) semiconductors, upon which a dozen layers of atoms are placed to form the part of the laser that generates light from quantum well
Quantum well
A quantum well is a potential well with only discrete energy values.One technology to create quantization is to confine particles, which were originally free to move in three dimensions, to two dimensions, forcing them to occupy a planar region...
s. Using methods similar to those developed for silicon, the substrate can be built free of the defects called dislocation
Dislocation
In materials science, a dislocation is a crystallographic defect, or irregularity, within a crystal structure. The presence of dislocations strongly influences many of the properties of materials...
s, and the atoms laid down so the distance between the ones making up the ground and those of the quantum well
Quantum well
A quantum well is a potential well with only discrete energy values.One technology to create quantization is to confine particles, which were originally free to move in three dimensions, to two dimensions, forcing them to occupy a planar region...
s are the same.
But the best semiconductor for blue lasers is gallium nitride (GaN) crystals, which are much harder to manufacture, requiring higher pressures and temperatures, similar to the ones that produce synthetic diamonds, and the use of high-pressure nitrogen gas. The technical problems seemed insurmountable, so researchers since the 1960s have sought to deposit GaN on a base of readily available sapphire
Sapphire
Sapphire is a gemstone variety of the mineral corundum, an aluminium oxide , when it is a color other than red or dark pink; in which case the gem would instead be called a ruby, considered to be a different gemstone. Trace amounts of other elements such as iron, titanium, or chromium can give...
. But a mismatch between the structures of sapphire and gallium nitride created too many defects.
In 1992 Japanese inventor Shuji Nakamura
Shuji Nakamura
is a professor at the Materials Department of the College of Engineering, University of California, Santa Barbara .- Career :Nakamura graduated from the University of Tokushima in 1977 with a degree in electronic engineering, and obtained a master's degree in the same subject two years later, after...
invented the first efficient blue LED, and four years later, the first blue laser. Nakamura used the material deposited on the sapphire substrate, although the number of defects remained too high (106–1010/cm2) to easily build a high-power laser.
In the early 1990s the Institute of High Pressure Physics at the Polish Academy of Sciences in Warsaw (Poland
Poland
Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...
), under the leadership of Dr. Sylwester Porowski
Sylwester Porowski
Sylwester Porowski , a Polish physicist specializing in solid-state and high pressure physics.In 2001 Professor Porowski's team built the blue semiconductor laser, a pioneering feat in the study of optoelectronics....
developed technology to create gallium nitride crystals with high structural quality and fewer than 100 defects per square centimeter — at least 10,000 times better than the best sapphire-supported crystal.
In 1999, Nakamura tried Polish crystals, producing lasers with twice the yield and ten times the lifetime — 3,000 hours at 30 mW.
A further development of the technology has led to mass production of the device. Today, blue lasers use a sapphire surface covered with a layer of gallium nitride (this technology is used by Japanese company Nichia, which has an agreement with Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
), and blue semiconductor lasers use a gallium nitride mono-crystal surface (Polish company TopGaN ).
After 10 years, Japanese manufacturers mastered the production of a blue laser with 60 mW of power, making them applicable for devices that read a dense high-speed stream of data from Blu-ray, BD-R, and BD-RE. Polish technology is cheaper than Japanese but has a smaller share of the market. There is one more Polish high-tech company which creates gallium nitride crystal – Ammono, but this company does not produce blue lasers.
For his work, Nakamura received the Millennium Technology Prize awarded in 2006.
Until the late 1990s, when blue semiconductor lasers were developed, blue lasers were large and expensive gas laser
Gas laser
A gas laser is a laser in which an electric current is discharged through a gas to produce coherent light. The gas laser was the first continuous-light laser and the first laser to operate "on the principle of converting electrical energy to a laser light output...
instruments which relied on population inversion
Population inversion
In physics, specifically statistical mechanics, a population inversion occurs when a system exists in state with more members in an excited state than in lower energy states...
in rare gas mixtures and needed high currents and strong cooling.
Thanks to prior development of many groups, including, most notably, Professor Isamu Akasaki
Isamu Akasaki
is a Japanese scientist, best known for inventing p-n junction blue LEDs using gallium nitride as early as 1989.-Blue LEDs:Akasaki was born in Kagoshima Prefecture in 1929, and received a Bachelor of Science degree in 1952 from Kyoto University. He received his PhD degree in Electronics from...
's group, Shuji Nakamura
Shuji Nakamura
is a professor at the Materials Department of the College of Engineering, University of California, Santa Barbara .- Career :Nakamura graduated from the University of Tokushima in 1977 with a degree in electronic engineering, and obtained a master's degree in the same subject two years later, after...
at Nichia Corporation
Nichia Corporation
The is a Japanese chemical engineering and manufacturing company, headquartered in Tokushima, Japan with global subsidiaries, that specializes in the manufacturing and distribution of phosphors, including light-emitting diodes , laser diodes, battery materials, and calcium chloride...
and Sony Corporation in Anan (Tokushima-ken, Japan) made a series of inventions and developed commercially viable blue and violet semiconductor lasers. The active layer of the Nichia devices was formed from InGaN
Indium gallium nitride
Indium gallium nitride is a semiconductor material made of a mix of gallium nitride and indium nitride . It is a ternary group III/group V direct bandgap semiconductor. Its bandgap can be tuned by varying the amount of indium in the alloy...
quantum well
Quantum well
A quantum well is a potential well with only discrete energy values.One technology to create quantization is to confine particles, which were originally free to move in three dimensions, to two dimensions, forcing them to occupy a planar region...
s or quantum dot
Quantum dot
A quantum dot is a portion of matter whose excitons are confined in all three spatial dimensions. Consequently, such materials have electronic properties intermediate between those of bulk semiconductors and those of discrete molecules. They were discovered at the beginning of the 1980s by Alexei...
s spontaneously formed via self-assembly
Self-assembly
Self-assembly is a term used to describe processes in which a disordered system of pre-existing components forms an organized structure or pattern as a consequence of specific, local interactions among the components themselves, without external direction...
. The new invention enabled the development of small, convenient and low-priced blue, violet, and ultraviolet UV lasers, which had not been available before, and opened the way for applications such as high-density HD DVD
HD DVD
HD DVD is a discontinued high-density optical disc format for storing data and high-definition video.Supported principally by Toshiba, HD DVD was envisioned to be the successor to the standard DVD format...
data storage and Blu-ray discs. The shorter wavelength allows it to read discs containing much more information.
Blue and violet diode-pumped solid state (DPSS) laser modules
Blue laser pointers, which became available around 2006, have the same basic construction as DPSS green lasers. They most commonly emit light at 473 nm (sometimes reported as 474 nm), which is produced by frequency doubling of 946 nm laser radiation from a diode-pumped Nd:YAG or Nd:YVO4 crystal. Neodymium-doped crystals usually produce a principal wavelength of 1064 nm, but with the proper reflective coating mirrors can be also made to lase at other non-principal neodymium wavelengths, such as the 946 nm transition used in blue-laser applications. For high output power BBOBeta Barium Borate
Beta barium borate is a crystal frequently used for frequency mixing and other nonlinear optics applications...
crystals are used as frequency doublers; for lower powers, KTP
Potassium titanyl phosphate
Potassium titanyl phosphate or KTP is a nonlinear optical material which is commonly used for frequency doubling diode pumped solid-state lasers such as Nd:YAG and other neodymium-doped lasers. The material has a relatively high optical damage threshold , a great optical nonlinearity and excellent...
is used. Output powers available are up to 1000 mW, but this usually is the total output including the infrared. As with green DPSS lasers, use of a 1000 mW IR diode usually results in approximately 300 mW of visible blue light, even if the laser is reported at 1000 mW power.
Blue lasers can also be fabricated directly with InGaN semiconductors, which produce blue light without frequency-doubling. 445 nm blue laser diodes are currently available on the open market. The devices are brighter than the 405 nm laser diodes, since the longer wavelength is closer to the peak sensitivity of the human eye. Commercial devices like laser projectors
Laser video projector
A laser video projector is a video projector that modulates a laser beam in order to project a raster-based image. The systems work either by scanning the entire picture a dot at a time and modulating the laser directly at high frequency, much like the electron beams in a CRT, or by optically...
have driven down the prices on these diodes, as of March 2011.
Violet lasers may be constructed directly with GaN (gallium nitride) semiconductors, as noted. However, a few higher-powered (120 mW) 404–405 nm "violet" laser pointers have become available which are not based on GaN, but also use DPSS frequency-doubler technology starting from 1 watt 808 nm gallium arsenide infrared diode lasers being directly doubled, without a longer-wave neodymium laser interposed between diode laser and doubler-crystal. As with all high powered lasers, such devices are able to pop balloons and light matches.
Appearance
The violet 405 nm laser (whether constructed from GaN or frequency-doubled GaAs laser diodes) is not in fact blue, but appears to the eye as violet, a color for which a human eye has a very limited sensitivity. When pointed at many white objects (such as white paper or white clothes which have been washed in certain washing powders) the visual appearance of the laser dot changes from violet to blue, due actually to fluorescenceFluorescence
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...
from brightening dyes.
For display applications which must appear "true blue", a wavelength of 450–460 nm is required. With advances in production, and commercial sales of low-cost laser projectors, 445 nm InGaN
Ingan
Ingan is a village in the Punjab province of Pakistan....
laser diodes have dropped in price.
A last challenge in projection laser diodes is related to the construction of a "true green" InGaN laser (around 530 nm). Many companies have demonstrated devices working at only slightly shorter wavelengths: 480–500 nm.
Applications
Areas of application of the blue laser include:- High-definition Blu-rayBlu-ray DiscBlu-ray Disc is an optical disc storage medium designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB per layer, with dual layer discs being the norm for feature-length video discs...
players - CasioCasiois a multinational electronic devices manufacturing company founded in 1946, with its headquarters in Shibuya, Tokyo, Japan. Casio is best known for its electronic products, such as calculators, audio equipment, PDAs, cameras, musical instruments, and watches...
and DLP brand projectors - Telecommunications
- Information technology
- Environmental monitoring
- Electronic equipment
- Medical diagnostics
- Micro projectors and displays