Ion laser


Ion laser

An ion laser is a gas laser which uses an ionized gas as its lasing medium. [GoldBookRef|title=ion laser|file=I03219] Like other gas lasers, ion lasers feature a sealed cavity containing the laser medium and mirrors forming a Fabry-Perot resonator. Unlike HeNe lasers, the energy level transitions that contribute to laser action come from ions. 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.

Types of lasers

A mix of argon and krypton can result in a laser with output wavelength appearing as white light.

Krypton laser

A krypton laser is an ion laser, a type of gas laser using krypton ions as a gain medium, pumped by electric 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 (eg. for coagulation of retina), 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 Aircraft and is one of a family of Ion lasers that use a noble gas as the active medium.

Argon lasers are used for retinal phototherapy (for diabetes), lithography, and pumping other lasers. Argon lasers emit at several wavelengths through the visible and ultraviolet spectrum: 351 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.

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 kovar, beryllium oxide ceramics, or copper. In comparison with the helium-neon lasers 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.

William R. Bennett was co-inventor of the first gas laser (the helium-neon laser), discovered the argon ion 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.

Gasses and gas mixtures found in ion lasers

Commercially available

* Argon ("argon laser")
* Krypton ("krypton laser")
* Ar/Kr mix ("white-light" laser")

Experimental

* Xenon [Hoffman Toschek, et. al., "The Pulsed Xenon Ion Laser: Covers the UV, visible, and near-IR with optics changes", IEEE Journal of Quantum Electronics]
* Iodine [Hattori, Kano, Tokutome and Collins, "CW Iodine Ion Laser in a Positive Column Discharge", IEEE Journal of Quantum Electronics, June 1974]
* Oxygen

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)

Models

* Melles Griot (Omnichrome) 532 ,543,643
* Lexel 75,85, 88, 95
* Laser ionics 557
* Spectra-Physics 161, 164 ,168, 171
* Coherent Innova 90, Innova 300, Sabre, Enterprise

Applications

* Surgical.
* High speed typesetters.
* Laser light shows.
* DNA sequencers for DNA sequencing.
* Spectroscopy experiments.
* Providing the source for tunable-dye lasers.
* Semiconductor mask inspection.
* Semiconductor wafer inspection.
* Direct write high density PCB lithography.
* Fiber Bragg Grating production.
* Long coherence length models can be used for holography.

Risks

* BeO
* electrical shock

See also

* Laser
* List of laser types

References


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