- Carbon dioxide laser
The carbon dioxide laser (CO2 laser) was one of the earliest
gas lasers to be developed (invented by Kumar Patelof Bell Labsin 1964 [cite journal
last = Patel
first = C. K. N.
authorlink = C. Kumar N. Patel
year = 1964
title = Continuous-Wave Laser Action on Vibrational-Rotational Transitions of CO2
journal = Physical Review
volume = 136
issue = 5A
pages = A1187–A1193
doi = 10.1103/PhysRev.136.A1187] ), and is still one of the most useful. Carbon dioxide lasers are the highest-power continuous wave
lasers that are currently available. They are also quite efficient: the ratio of output power to pump power can be as large as 20%.
The CO2 laser produces a beam of
infrared lightwith the principal wavelengthbands centering around 9.4 and 10.6 micrometers.
active laser medium(laser gain/amplification medium) is a gas dischargewhich is air cooled (water cooled in higher power applications). The filling gas within the discharge tube consists primarily of:
Carbon dioxide(chem|CO|2) (around 10–20 %)
Nitrogen(chem|N|2) (around 10–20%)
Hydrogen(chem|H|2) and/or xenon(Xe) (a few percent; usually only used in a sealed tube.)
Helium(He) (The remainder of the gas mixture)The specific proportions vary according to the particular laser.
population inversionin the laser is achieved by the following sequence:
Electronimpact excites vibrational motion of the nitrogen. Because nitrogen is a homonuclear molecule, it cannot lose this energy by photonemission, and its excited vibrational levels are therefore metastable and live for a long time.
# Collisional energy transfer between the nitrogen and the carbon dioxide molecule causes vibrational excitation of the carbon dioxide, with sufficient efficiency to lead to the desired population inversion necessary for laser operation.
Because CO2 lasers operate in the infrared, special materials are necessary for their construction. Typically, the
mirrors are made of coated silicon, molybdenum, or gold, while windows and lenses are made of either germaniumor zinc selenide. For high power applications, gold mirrors and zinc selenide windows and lenses are preferred. There are also diamondwindows and even lenses in use. Diamond windows are extremely expensive, but their high thermal conductivity and hardness makes them useful in high-power applications and in dirty environments. Optical elements made of diamond can even be sand blasted without losing their optical properties. Historically, lenses and windows were made out of salt (either sodium chlorideor potassium chloride). While the material was inexpensive, the lenses and windows degraded slowly with exposure to atmospheric moisture.
The most basic form of a CO2 laser consists of a gas discharge (with a mix close to that specified above) with a total reflector at one end, and an output coupler (usually a semi-reflective coated zinc selenide mirror) at the output end. The reflectivity of the
output coupleris typically around 5-15%. The laser output may also be edge-coupled in higher power systems to reduce optical heating problems.
The CO2 laser can be constructed to have CW powers between
milliwatts (mW) and hundreds of kilowatts (kW). [ [http://www.afrlhorizons.com/Briefs/Feb04/ML0315.html Air Force Research Lab's 150 kW CO2 Laser] ] It is also very easy to actively Q-switch a CO2 laser by means of a rotating mirror or an electro-optic switch, giving rise to Q-switched peak powers up to gigawatts (GW) of peak power [ [http://www.bnl.gov/atf/core_capabilities/co2amp.asp Brookhaven National Lab's Carbon Dioxide Amplifier] ] .
Because the laser transitions are actually on vibration-rotation bands of a linear triatomic molecule, the rotational structure of the P and R bands can be selected by a tuning element in the
laser cavity. Because transmissive materials in the infrared are rather lossy, the frequencytuning element is almost always a diffraction grating. By rotating the diffraction grating, a particular rotational line of the vibrational transition can be selected. The finest frequency selection may also be obtained through the use of an etalon. In practice, together with isotopic substitution, this means that a continuous comb of frequencies separated by around 1 cm-1 (30 GHz) can be used that extend from 880 to 1090 cm-1. Such "line-tuneable" carbon dioxide lasers are principally of interest in research applications.
Because of the high power levels available (combined with reasonable cost for the laser), CO2 lasers are frequently used in industrial applications for
cuttingand welding, while lower power level lasers are used for engraving. They are also very useful in surgical procedures because water (which makes up most biological tissue) absorbs this frequency of light very well. Some examples of medical uses are laser surgery, skin resurfacing ("laser facelifts") (which essentially consist of burning the skin to promote collagen formation), and dermabrasion. Also, it could be used to treat certain skin conditions such as hirsuties papillaris genitalisby removing embarrassing or annoying bumps, podules, etc.
Laser beam profiler
* [http://repairfaq.ece.drexel.edu/sam/lasercc2.htm Home-built Carbon dioxide laser]
Wikimedia Foundation. 2010.
Look at other dictionaries:
carbon-dioxide laser — anglies dioksido lazeris statusas T sritis radioelektronika atitikmenys: angl. carbon dioxide laser vok. Kohlendioxid Laser, m rus. лазер на углекислом газе, m pranc. laser à dioxyde carbonique, m … Radioelektronikos terminų žodynas
carbon-dioxide laser — laser with carbon dioxide gas as the active means that produces infrared radiation at 10,600 nanometer … English contemporary dictionary
carbon-dioxide laser — a laser with carbon dioxide gas as the active medium that produces infrared radiation at 10,600 nm; used to excise and incise tissue and to vaporize … Medical dictionary
carbon dioxide laser — noun a device using contained carbon dioxide gas to produce a laser beam with shallow penetration and minimal heat production, that is used as a cutting implement in various medical treatments … Australian English dictionary
high-pressure carbon dioxide laser — didžiaslėgis anglies dioksido lazeris statusas T sritis radioelektronika atitikmenys: angl. high pressure carbon dioxide laser vok. Hochdruck Kohlendioxid Laser, m rus. лазер высокого давления на углекислом газе, m pranc. laser à dioxyde de… … Radioelektronikos terminų žodynas
Carbon dioxide — Carbon dioxide … Wikipedia
Laser beam welding — (LBW) is a welding technique used to join multiple pieces of metal through the use of a laser. The beam provides a concentrated heat source, allowing for narrow, deep welds and high welding rates. The process is frequently used in high volume… … Wikipedia
Laser engraving — is the practice of using lasers to engrave or mark an object. The technique can be very technical and complex, and often a computer system is used to drive the movements of the laser head. Despite this complexity, very precise and clean… … Wikipedia
Laser-hybrid welding — is a type of welding process that combines the principles of laser beam welding and arc welding. Introduction The combination of laser light and an electrical arc into an amalgamated welding process has beenknown since the 1970 s, but has only… … Wikipedia
Laser resurfacing — is a technique used during laser surgery wherein molecular bonds of a material are dissolved by a laser. It is used for the treatment of wrinkles, solar lentigenes, sun damage, scars (see acne scar treatment), stretch marks, actinic keratosis and … Wikipedia