He- Ne 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. The best known and most widely used HeNe laser operates at a wavelength of 632.8 nm in the red part of the visible spectrum.

CO2 Laser

The carbon dioxide laser (CO₂ laser) was one of the earliest gas lasers to be developed (invented by Kumar Patel of Bell Labs in 1964), 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%.

Because CO₂ lasers operate in the infrared, special materials are necessary for their construction. Typically, the mirrors are silvered, while windows and lenses are made of either germanium orzinc selenide. For high power applications, gold mirrors and zinc selenide windows and lenses are preferred. There are also diamond windows and even lenses in use. Diamond windows are extremely expensive, but their high thermal conductivity and hardness make 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 chloride or 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 (a partially reflecting mirror) at the output end.^[2] 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).^[3] 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 of up to gigawatts (GW).^[4]

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 frequency tuning 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^[5] are principally of interest in research applications.

Laser

Carbon Dioxide Laser ( CO_2 ) is a molecular gas discharge laser.In this laser the transition take place between vibrational levels.These lasers having high efficiency ,operational both in continous wave and pulsed mode are known for high power generation.Yhis stimulates the improvement of modern CO_2 lasers and construction of new one's to increase the power and brightness of the radiation and to improve their economical and constructional characteristics.In recent year a much attention was given to multibeam co_2 lasers in view of obtaining high power.The distinguishing characteristic of the CO_2 lasing process that makes these sustained power levels possible is its relatively high efficiency at least compared to most other common gas lasers.Unlike the other lasers producing visible or short near-IR light, the output of a CO_2 laser is medium-IR radiation at 10.6 um. At this wavelength, normal glass and plastics are opaque, and water completely absorbs the energy in the beam. The 10.6 um energy is ideal for cutting, engraving, welding, heat treating, and other industrial processing of many types of materials including (as appropriate)  metals, ceramics, plastics, wood, paper, cardboard, fabric, composites, and much much more. Needless to say, 10.6 um is totally invisible to the human eye and conventional solid state sensors are blind as a post. Therefore, thermal approaches are generally used to measure beam power or determine beam profile by CO_2 laser view plates,power meter and spectrum analyzer.