CO2 Lasers

The Carbon Dioxide Laser is a type of aesthetic laser used in cosmetic procedures, and is the first laser ever to be used as a surgical tool. The CO2 laser is an ablative laser, which means that it vaporizes skin on the surface, effectively removing the top-most layers of the skin. The CO2 laser can be focused down to a very thin beam and used to cut like a scalpel, or in a defocused mode to vaporize or ablate soft tissue. In cosmetic applications, the CO2 laser is typically used to address skin problems such as lines and wrinkles, unwanted tattoos, acne and other scars, and for skin tightening.

By delivering very powerful, rapid pulsing or scanning of the latest generation of CO2 lasers, laser surgeons are able to resurface the skin for cosmetic improvement. This technique removes fine lines and wrinkles of the face, smoothes acne scars, and rejuvenates aging and sun-damaged skin as it contours the skin surface. When the CO2 laser’s energy is defocused and not continuous (pulsed), the dermasurgeon can treat warts, shallow tumors and certain precancerous conditions. When the CO2 laser energy is continuous and focused into a small spot of light, the beam is able to cut the skin. It is used in this way to remove skin cancers, to treat a variety of non-vascular and pigmented lesions and for eyelid operations. This technique is also used to remove warts and for some surgical incisions.

History of the the CO2 laser:  Carbon dioxide laser (CO2 laser) was one of the earliest gas lasers to be developed (invented by Kumar Patel of Bell Labs in 1964[1]), 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%.

Specifications:
The CO2 laser produces a beam of infrared light with the principal wavelength bands centering around 9.4 and 10.6 micrometers.

Amplification:
The active laser medium (laser gain/amplification medium) is a gas discharge which is air cooled (water cooled in higher power applications).

The filling gas within the discharge tube consists primarily of:
• Carbon dioxide (CO2) (around 10–20 %)
• Nitrogen (N2) (around 10–20%)
• Hydrogen (H2) and/or xenon (Xe) (a few percent; usually only used in a sealed tube.)
• Helium (He) (The remainder of the gas mixture)

Construction:
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 or zinc 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 (usually a semi-reflective coated zinc selenide mirror) at the output end. The reflectivity of the output coupler is typically around 5-15%. The laser output may also be edge-coupled in higher power systems to reduce optical heating problems.

Applications:
Because of the high power levels available (combined with reasonable cost for the laser), CO2 lasers are frequently used in industrial applications for cutting and 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 genitalis by removing embarrassing or annoying bumps, podules, etc.