Ion laser
Encyclopedia
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...
which uses an ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
ized 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
Helium-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:...
, the energy level transitions that contribute to laser action come from ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s. Because of the large amount of energy required to excite the ionic transitions used in ion lasers, the required current is much greater, and as a result all but the smallest ion lasers are water-cooled. A small air-cooled ion laser might produce, for example, 130mW of light with a tube current of 10A @ 105V. This is a total power draw over 1 kW, which translates into a large amount of heat which must be dissipated.
Krypton laser
A krypton laser is an ion laser, a type of gas laserGas 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...
using krypton
Krypton
Krypton is a chemical element with the symbol Kr and atomic number 36. It is a member of Group 18 and Period 4 elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionally distilling liquified air, and is often used with other...
ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s as a gain medium, pumped
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...
by electric discharge
Electric discharge
Electric discharge describes any flow of electric charge through a gas, liquid or solid. Electric discharges include:*Electric glow discharge*Electric arc*Electrostatic discharge*Electric discharge in gases*Leader *Partial discharge...
. Krypton lasers are used for scientific research, or when krypton is mixed with argon, for creation of "white-light" lasers, useful for laser light shows. Krypton lasers are also used in medicine (e.g. for coagulation of 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...
), for manufacture of security holograms, and numerous other purposes.
Krypton lasers emit at several wavelengths through the visible spectrum: at 406.7 nm, 413.1 nm, 415,4 nm, 468.0 nm, 476.2 nm, 482.5 nm, 520.8 nm, 530.9 nm, 568.2 nm, 647.1 nm, 676.4 nm.
Argon laser
The Argon laser was invented in 1964 by William Bridges at Hughes AircraftHughes Aircraft
Hughes Aircraft Company was a major American aerospace and defense contractor founded in 1932 by Howard Hughes in Culver City, California as a division of Hughes Tool Company...
and is one of a family of Ion lasers that use a noble gas as the active medium.
Argon lasers are used for 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...
l phototherapy (for diabetes), lithography
Lithography
Lithography is a method for printing using a stone or a metal plate with a completely smooth surface...
, and pumping
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...
other lasers. Argon lasers emit at 13 wavelengths through the visible, ultraviolet, and near-visible spectrum, including: 351.1 nm, 363.8 nm, 454.6 nm, 457.9 nm, 465.8 nm, 476.5 nm, 488.0 nm, 496.5 nm, 501.7 nm, 514.5 nm, 528.7 nm, 1092.3 nm.
Common argon and krypton lasers are capable of emitting continual wave output of several milliwatts to tens of watts continually. Their tubes are usually made of Nickel end bells, kovar
Kovar
Kovar is a nickel-cobalt ferrous alloy designed to be compatible with the thermal expansion characteristics of borosilicate glass in order to allow direct mechanical connections over a range of temperatures...
metal to ceramic seals, beryllium oxide
Beryllium oxide
Beryllium oxide , also known as beryllia, is an inorganic compound with the formula BeO. This colourless solid is a notable electrical insulator with a higher thermal conductivity than any other non-metal except diamond, and actually exceeds that of some metals. As an amorphous solid, beryllium...
ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
s, or tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
disks mounted on a copper heat spreader in a ceramic liner. The earliest tubes were simple quartz, followed by quartz with graphite disks. In comparison with the helium-neon laser
Helium-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 requiring just a few milliamps, the current used for pumping the krypton laser ranges in several amperes, as the gas has to be ionized. The ion laser tube produces a lot of waste heat and requires active cooling.
The typical noble gas ion laser plasma consists of a high-current-density glow discharge in a noble gas, in the presence of a magnetic field. Typical CW plasma conditions are current densities of 100 to 2000 A/cm^2, tube diameters of 1 to 10 mm, filling pressures of 0.1 to 1.0 torr, and an axial magnetic field of the order of 1000 G.
(Bridges,Halstead et al., Proceedings of the IEEE, 59 (5). pp. 724-739)
William R. Bennett
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:...
was co-inventor of the first gas laser (the helium-neon laser), was first to observe spectral hole burning effects in gas lasers, and created a theory of hole burning effects on laser oscillation. He was co-discoverer of lasers using electron impact excitation in each of the noble gases, dissociative excitation transfer in the neon-oxygen laser (the first chemical laser), and collision excitation in several metal vapor lasers.
Other commercially available types
- Ar/Kr: A mix of argon and krypton can result in a laser with output wavelengths that appear as white light.
- Helium Cadmium, Blue laser emission at 442 nm and Ultraviolet at 325 nm
- Copper Vapor, Yellow and Green emission at 578 nm and 510 nm
Power supplies
- NPN passbank like the Spectra-physics 270 supply
- MOSFET switchers like the Omnichrome 150 supply
- Early switchers used NPN_PNP Pairs, (i.e. American Laser or HGM Medical)
- IGBT will be seen more in days to come
- Switched resistor (Spectra Physics)
- Non-switched resistor (Home-made, typically a water heater element)
- Water-cooled resistor (Laser Ionics etc.)
- Phased SCR power supplies similar to long xenon arc lamps are used in medical lasers to reduce expense (Coherent)
- Power on Demand power supplies are used for pulsed medical ion laser systems, these power supplies consist of a large capacitor bank charged by a switching supply to enable multi watt lasers to run off common single phase power supplies in doctor's offices.
- A typical air-cooled Argon Tube needs an equivalent series resistance of ~6 Ohms when running @ 10 amps off 117V power. The plasma in an ion laser, unlike a Helium Neon Laser, has a slightly positive resistance, but will still run away without ballasting. This is why ion laser supplies are very difficult to design. On a large frame laser, the plasma itself has an effective resistance of about -7 Ohms (Spectra Physics 171 Service Manual)
Applications
- SurgicalSurgerySurgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...
. - Laser medicineLaser medicineLaser medicine is the use of various types of lasers in medical diagnosis, treatment, or therapy. Types of lasers used in medicine include in principle any laser design, especially:* CO2 lasers* diode lasers* dye lasers* excimer lasers* fiber lasers...
. - High speed typesetters.
- Laser light showsLaser lighting displayA laser lighting display or laser light show involves the use of laser light to entertain an audience. A laser light show may consist only of projected laser beams set to music, or may accompany another form of entertainment, typically a dance concert or other musical performance.Laser light is...
. - DNA sequencerDNA sequencerA DNA sequencer is a scientific instrument used to automate the DNA sequencing process. It can be also considered an optical instrument as it generally analyses light signals originating from fluorochromes attached to nucleotides....
s for DNA sequencingDNA sequencingDNA sequencing includes several methods and technologies that are used for determining the order of the nucleotide bases—adenine, guanine, cytosine, and thymine—in a molecule of DNA....
. - SpectroscopySpectroscopySpectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
experiments. - Providing the excitation source for tunable dye laserDye laserA dye laser is a laser which uses an organic dye as the lasing medium, usually as a liquid solution. Compared to gases and most solid state lasing media, a dye can usually be used for a much wider range of wavelengths. The wide bandwidth makes them particularly suitable for tunable lasers and...
s. - Semiconductor mask inspectionMask inspectionIn microtechnology, mask inspection or photomask inspection is an operation of checking the correctness of the fabricated photomasks, used, e.g., for semiconductor device fabrication....
. - Semiconductor wafer inspection.
- Direct write high density PCB lithographyLithographyLithography is a method for printing using a stone or a metal plate with a completely smooth surface...
. - Fiber Bragg GratingFiber Bragg gratingA fiber Bragg grating is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. This is achieved by adding a periodic variation to the refractive index of the fiber core, which generates a...
production. - Long coherence length models can be used for holography.