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. The first gas laser, the Helium–neon laser (HeNe), was co-invented by Iranian-Azerbaijani physicist 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.
The helium–neon (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) 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 monoxide 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.
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.
A nitrogen transverse electrical discharge in gas at atmospheric pressure (TEA) laser is an inexpensive gas laser producing UV light at 337.1 nm.
Copper laser (copper vapor, and copper bromide vapor), 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.
Metal ion lasers are gas lasers that typically generate ultraviolet wavelengths. Helium-silver (HeAg) 224 nm neon-copper (NeCu) 248 nm and helium-cadmium (HeCd) 325 nm are three examples. These lasers have particularly narrow oscillation linewidths of less than 3 GHz (0.5 picometers), making them candidates for use in fluorescence suppressed Raman spectroscopy.
Chemical lasers are powered by a chemical reaction, and can achieve high powers in continuous operation. For example, in the hydrogen fluoride laser (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 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, however continuous wave chemical lasers at very high power levels, fed by streams of gasses, have been developed and have some industrial applications. As examples, in the hydrogen fluoride laser (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 in nitrogen trifluoride
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 light, and are used in semiconductor photolithography and in LASIK eye surgery. Commonly used excimer molecules include F2 (fluorine, emitting at 157 nm), and noble gas compounds (ArF [193 nm], KrCl [222 nm], KrF [248 nm], XeCl [308 nm], and XeF [351 nm]).
- 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
- 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.
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