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While non-ablative lasers were less invasive than ablative lasers, they proved to be weaker. Because of this, fractionated cosmetic lasers were developed. Fractionated, fractional, or fractionally means that a laser beam is split into hundreds of tiny beams (a bunch of dots) instead of one solid beam. When a fractionated laser penetrates your skin, it penetrates in a scattered way, treating some skin while leaving skin in between alone.   Your skin is only fractionally treated with a laser because the laser beam has been split up (think string cheese instead of a block of cheese). Instead of getting one solid dose of laser in a specific area of your skin, you get a spread out dose, receiving the same benefits minus the downtime. The 1st fractionated laser was Fraxel, any type of laser can be fractionated ablative lasers, fractionated non-ablative lasers, fractionated CO2 lasers, fractionated Nd:Yags, etc. 

Continuous Wave: A continuous wave (CW) laser is a laser beam that is constant. The laser emits high energy light non-stop, unlike pulsed lasers which emit laser beams in short bursts. Old cosmetic laser technologies like carbon dioxide lasers and argon lasers are examples of continuous wave lasers. CW lasers are not used to treat facial skin anymore because there are other lasers that produce the same results without such severe side effects and downtime.



Quality switch .Very high intensity laser beam is emitted suddenly when the energy within the device reaches the peak level much beyond population inversion and then stops till energy reaches another peak.

Q-switching refers to the technique of making a laser produce a high intensity beam in very short pulses. Q-switched lasers are a type of pulsed laser, but they are short-pulsed pulsed lasers with durations of 5-100 nanoseconds. Q-switched lasers are usually used for tattoo removal on skin.

The rate of thermal diffusion of a given tissue is known as the thermal relaxation time (TR) and is defined as the time required for a given heated tissue to lose 50% of its heat through diffusion. It is measured in terms of the area affected and the thermal diffusivity (D) of the target tissue, as TR = r2/4 D, where r is the radius of target tissue.
Therefore, significant thermal diffusion (and hence thermal damage) is minimized if the duration of the laser pulse is shorter than the TR of the target tissue.
For example, water (the primary constituent by weight of living cells) has a high absorption coefficient of 230 cm-1 at 10,600 nm, the wavelength emission of a CO2laser, and a TR of 326 µs. With these properties, if a CO2 laser contacts the skin for less than 326 µs, most of the radiation is absorbed by the water in the targeted skin, with almost no thermal diffusion. However, if the duration of the laser impingement on the tissue is longer than 326 µs, heat is transmitted to the surrounding non targeted tissue and results in undesirable thermal injury.

Therefore, for proper SP to occur, the target tissue (through its chromophores) must possess greater optical absorption than the non targeted surrounding tissue does, and the laser of choice must have a pulse duration shorter than the TR of the target tissue. Because soft tissues in humans generally have a TR of less than 1 ms, the laser pulse must be extremely short and high-powered to be medically beneficial and minimally destructive. Because many types of lasers exist, selection is crucial and must be tailored to the specific procedure.

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