Laser Parameters

Several wavelengths of laser energy have been used for hair removal, from visible light to near-infrared radiation. These lasers are usually defined by the lasing medium used to create the wavelength (measured in nanometers (nm)):

* Argon: 488 or 514.5 nm (no longer used for hair removal)
* Ruby: 694 nm (no longer used for hair removal; not safe on most skin types as it frequently produces side effects such as pigmentary changes (lightening or darkening of the skin) or worse for patients of all but white skin.[citation needed]
* Alexandrite: 755 nm (most effective, but safest on light skin)
* Pulsed diode array: 810 nm (for light to medium type skin)
* Nd:YAG: 1064 nm (for darker skin; Yag is capable of treating all six skin colors. However, there is not sufficient evidence that this laser can produce effective long-term hair removal)

Pulsewidth is an important consideration. It has been observed in some published studies that longer pulse widths may be safer for darker skin. However, shorter wavelengths may be more effective in removing hair.

Spot size, or the width of the laser beam, affects treatment. Theoretically, the width of the ideal beam is about four times as wide as the target is deep. Hair removal lasers have a round spot about the size of your finger (8-18 mm). Larger spot sizes help make treatments faster and more effective.

Fluence or energy level is another important consideration. Fluence is measured in joules per square centimeter (J/cm²). It's important to get treated at high enough settings to cause permanent damage to the hair follicles.

Repetition rate is believed to have a cumulative effect, based on the concept of thermal relaxation time. Shooting two or three pulses at the same target with a specific delay between pulses can cause a slight improvement in the heating of an area. This may increase the "kill rate" for each treatment slightly.

Epidermal cooling has been determined to allow higher fluences and reduce pain and side effects, especially in darker skin. Four types of cooling have been developed:

* Clear gel: usually chilled
* Contact cooling: through a window cooled by circulating water or internal cryogen.
* Cryogen spray: immediately before/after the laser pulse
* Air cooling: forced cold air at -34 degrees C (Zimmer Cryo 5 unit)

Multiple treatments, usually 6-8, but as much as 12 depnding on the type of hair you have and skin color have been shown in numerous studies to provide long-term reduction of hair. Current parameters suggest a series of treatments spaced at 4-6 weeks apart for most areas, although the timing of treatments has still not been standardized.