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A gas laser is a
laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...
in which an
electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...
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. The first gas laser, the Helium–neon laser (HeNe), was co-invented by Iranian engineer and scientist Ali Javan and American physicist William R. Bennett, Jr., in 1960. It produced a coherent light beam in the infrared region of the spectrum at 1.15 micrometres.


Types of gas laser

Gas lasers using many gases have been built and used for many purposes.
Carbon dioxide laser The carbon-dioxide laser (CO2 laser) was one of the earliest gas lasers to be developed. It was invented by C. Kumar N. Patel, Kumar Patel of Bell Labs in 1964 and is still one of the most useful types of laser. Carbon dioxide, Carbon-dioxide lase ...
s, or lasers can emit hundreds of kilowatts at 9.6  μm and 10.6 Î¼m, and are often used in industry for cutting and welding. The efficiency of a laser is over 10%.
Carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...
or "CO" lasers have the potential for very large outputs, but the use of this type of laser is limited by the toxicity of carbon monoxide gas. Human operators must be protected from this deadly gas. Furthermore, it is extremely corrosive to many materials including seals, gaskets, etc. Helium–neon (HeNe) lasers can be made to oscillate at over 160 different wavelengths by adjusting the cavity Q to peak at the desired wavelength. This can be done by adjusting the spectral response of the mirrors or by using a dispersive element (
Littrow prism In optics, a Littrow prism, or Littrow mirror, originally part of a Littrow spectrograph (after Otto von Littrow), is a retro-reflecting, dispersing prism arranged in such a way that an incident light beam which enters at the Brewster angle underg ...
) in the cavity. Units operating at 633 nm are very common in schools and laboratories because of their low cost and near-perfect beam qualities. Nitrogen lasers operate in the ultraviolet range, typically 337.1 nm, using molecular nitrogen as its gain medium, pumped by an electrical discharge. TEA lasers are energized by a high voltage electrical discharge in a gas mixture generally at or above atmospheric pressure. The acronym "TEA" stands for Transversely Excited Atmospheric.


Chemical lasers

Chemical lasers are powered by a chemical reaction and can achieve high powers in continuous operation. For example, in the hydrogen fluoride laser (2.7–2.9 μm) and the deuterium fluoride laser (3.8 μm) the reaction is the combination of hydrogen or deuterium gas with combustion products of ethylene in nitrogen trifluoride. They were invented by George C. Pimentel. Chemical lasers are powered by a chemical reaction permitting a large amount of energy to be released quickly. Such very high power lasers are especially of interest to the military. Further, continuous-wave chemical lasers at very high power levels, fed by streams of gasses, have been developed and have some industrial applications.


Excimer lasers

Excimer lasers are powered by a chemical reaction involving an ''excited dimer'', or '' excimer'', which is a short-lived dimeric or heterodimeric molecule formed from two species (atoms), at least one of which is in an excited electronic state. They typically produce
ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...
light, and are used in semiconductor
photolithography Photolithography (also known as optical lithography) is a process used in the manufacturing of integrated circuits. It involves using light to transfer a pattern onto a substrate, typically a silicon wafer. The process begins with a photosensiti ...
and in
LASIK LASIK or Lasik (; "laser-assisted in situ keratomileusis"), commonly referred to as laser eye surgery or laser vision correction, is a type of refractive surgery for the correction of myopia, hyperopia, and astigmatism. LASIK surgery is p ...
eye surgery. Commonly used excimer molecules include F2 (
fluorine Fluorine is a chemical element; it has Chemical symbol, symbol F and atomic number 9. It is the lightest halogen and exists at Standard temperature and pressure, standard conditions as pale yellow Diatomic molecule, diatomic gas. Fluorine is extre ...
, emitting at 157 nm), and noble gas compounds (ArF 93 nm KrCl 22 nm KrF 48 nm XeCl 08 nm and XeF 51 nm.


Ion lasers

Argon-ion lasers emit light in the range 351–528.7 nm. Depending on the optics and the laser tube a different number of lines is usable but the most commonly used lines are 458 nm, 488 nm and 514.5 nm.


Metal-vapor lasers

Metal-vapor lasers are gas lasers that typically generate
ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...
wavelengths.
Helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...
-
silver Silver is a chemical element; it has Symbol (chemistry), symbol Ag () and atomic number 47. A soft, whitish-gray, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. ...
(HeAg) 224 nm,
neon Neon is a chemical element; it has symbol Ne and atomic number 10. It is the second noble gas in the periodic table. Neon is a colorless, odorless, inert monatomic gas under standard conditions, with approximately two-thirds the density of ...
-
copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
(NeCu) 248 nm and
helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...
- cadmium (HeCd) 325 nm are three examples. These lasers have particularly narrow oscillation linewidths of less than 3 
GHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or Cycle per second, cycle) per second. The hertz is an SI derived unit whose formal expression in ter ...
(500 femtometers), making them candidates for use in
fluorescence Fluorescence is one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with colore ...
suppressed Raman spectroscopy. The Copper vapor laser, with two spectral lines of green (510.6 nm) and yellow (578.2 nm), is the most powerful laser with the highest efficiency in the visible spectrum.


Advantages

* High volume of active material * Active material is relatively inexpensive * Almost impossible to damage the active material * Heat can be removed quickly from the cavity


Applications

* He-Ne laser is mainly used in making holograms. * In laser printing He-Ne laser is used as a source for writing on the photosensitive material. * He-Ne lasers were used in reading Bar Codes, which are imprinted on products in stores. They have been largely replaced by laser diodes. * Nitrogen lasers and excimer laser are used in pulsed dye laser pumping. * Ion lasers, mostly argon, are used in CW dye laser pumping.


See also

* Gas dynamic laser * Brewster window * List of laser types


References

* * {{Lasers American inventions