Gas laser

Gas laser

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A gas laser is a laser
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...

 in which an electric current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...

 is discharged through a gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

 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 physicist Ali Javan
Ali Javan
Ali Mortimer Javan , born December 26, 1926 in Tehran, Iran is an Iranian American inventor and physicist at MIT. He co-invented the gas laser in 1960, with William R. Bennett...

 and American physicist William R. Bennett, Jr.
William R. Bennett, Jr.
William Ralph Bennett Jr. was an American physicist known for his pioneering work on gas lasers. He spent most of his career on the faculty of Yale University.-Career:...

 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.

The Helium–neon or HeNe laser 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
Littrow prism
In optics, a Littrow prism is a retro-reflecting dispersing prism arranged in such a way that an incident light beam which enters at the Brewster angle undergoes minimal deviation and hence maximum dispersion. Littrow prisms are typically 30° - 60° - 90° prisms, with a a reflective film coating on...

) 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.

Carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

, or CO2 lasers can emit hundreds of kilowatts at 9.6 µm and 10.6 µm, and are often used in industry for cutting and welding. The efficiency of a CO2 laser is over 10%.

Carbon Monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 or "CO" lasers have the potential for very large outputs, but the use of this type of laser is limited by the extreme toxicity of Carbon Monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 gas. Human operators must be protected from this deadly gas and it is extremely corrosive to many materials included seals, gaskets, etc. Thus extreme care must be used when constructing and using CO lasers.

Argon-ion
Ion laser
An ion laser is a gas laser which uses an ionized gas as its lasing medium.Like other gas lasers, ion lasers feature a sealed cavity containing the laser medium and mirrors forming a Fabry–Pérot resonator. Unlike HeNe lasers, the energy level transitions that contribute to laser action come from ions...

 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.

A nitrogen transverse electrical discharge in gas at atmospheric pressure
TEA laser
A TEA laser is a transversely-excited atmospheric-pressure laser.-Invention:The CO2 TEA laser was invented in the late 1960s by Dr Jacques Beaulieu working at the Defence Research Establishment, Valcartier, in Quebec, Canada...

  (TEA) laser is an inexpensive gas laser producing UV light at 337.1 nm.

Metal ion lasers are gas lasers that generate deep ultraviolet wavelengths. Helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

-silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...

 (HeAg) 224 nm and neon
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...

-copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 (NeCu) 248 nm are two examples. These lasers have particularly narrow oscillation linewidths of less than 3 GHz
GHZ
GHZ or GHz may refer to:# Gigahertz .# Greenberger-Horne-Zeilinger state — a quantum entanglement of three particles.# Galactic Habitable Zone — the region of a galaxy that is favorable to the formation of life....

 (0.5 picometers), making them candidates for use in 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...

 suppressed Raman spectroscopy
Raman spectroscopy
Raman spectroscopy is a spectroscopic technique used to study vibrational, rotational, and other low-frequency modes in a system.It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range...

.
  • Nitrogen laser
    Nitrogen laser
    A nitrogen laser is a gas laser operating in the ultraviolet range using molecular nitrogen as its gain medium, pumped by an electrical discharge....

  • Ion laser
    Ion laser
    An ion laser is a gas laser which uses an ionized gas as its lasing medium.Like other gas lasers, ion lasers feature a sealed cavity containing the laser medium and mirrors forming a Fabry–Pérot resonator. Unlike HeNe lasers, the energy level transitions that contribute to laser action come from ions...

  • Gas dynamic laser
    Gas dynamic laser
    Gas Dynamic Laser is laser based on differences in relaxation velocities of molecular vibrational states.The laser medium gas has such properties that an energetically lower vibrational state relaxes faster than a higher vibrational state,...


Chemical lasers


Chemical laser
Chemical laser
A chemical laser is a laser that obtains its energy from a chemical reaction. Chemical lasers can achieve continuous wave output with power reaching to megawatt levels...

s are powered by a chemical reaction, and can achieve high powers in continuous operation. For example, in the Hydrogen fluoride laser
Hydrogen fluoride laser
The hydrogen fluoride laser is an infrared chemical laser. It is capable of delivering continuous output power in the megawatt range.Hydrogen fluoride lasers operate at the wavelength of 2.7-2.9 µm. This wavelength is absorbed by the atmosphere, effectively attenuating the beam and reducing its...

 (2700–2900 nm) and the Deuterium fluoride laser (3800 nm) the reaction is the combination of hydrogen or deuterium gas with combustion products of ethylene
Ethylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...

 in nitrogen trifluoride
Nitrogen trifluoride
Nitrogen trifluoride is the inorganic compound with the formula NF3. This nitrogen-fluorine compound is a colorless, toxic, odourless, nonflammable gas. It finds increasing use as an etchant in microelectronics.-Applications:...

. They were invented by George C. Pimentel
George C. Pimentel
George Claude Pimentel was the inventor of the chemical laser. He also developed the modern technique of matrix isolation in low-temperature chemistry. In theoretical chemistry, he proposed the three-centre four-electron bond which is now accepted as the best simple model of hypervalent...

.

Excimer lasers


Excimer laser
Excimer laser
An excimer laser is a form of ultraviolet laser which is commonly used in the production of microelectronic devices , eye surgery, and micromachining....

s are powered by a chemical reaction involving an excited dimer, or excimer
Excimer
An excimer is a short-lived dimeric or heterodimeric molecule formed from two species, at least one of which is in an electronic excited state. Excimers are often diatomic and are composed of two atoms or molecules that would not bond if both were in the ground state. The lifetime of an excimer is...

, 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
Excited state
Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being excited to an excited state....

. They typically produce 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...

 light, and are used in semiconductor photolithography
Photolithography
Photolithography is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate...

 and in LASIK
LASIK
LASIK or Lasik , commonly referred to simply as laser eye surgery, is a type of refractive surgery for correcting myopia, hyperopia, and astigmatism...

 eye surgery. Commonly used excimer molecules include F2 (fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...

, emitting at 157 nm), and noble gas compounds (ArF [193 nm], KrCl [222 nm], KrF [248 nm], XeCl [308 nm], and XeF [351 nm]).

Advantages

  • High volume of active material
    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...

  • Active material is relatively inexpensive
  • Almost impossible to damage the active material
  • Heat can be removed quickly from the cavity
    Optical cavity
    An optical cavity or optical resonator is an arrangement of mirrors that forms a standing wave cavity resonator for light waves. Optical cavities are a major component of lasers, surrounding the gain medium and providing feedback of the laser light. They are also used in optical parametric...


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 the Bar Code which is imprinted on the product. 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.