September 20, 2007

Laser parameters that affect results  

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 (not used for hair removal anymore)
• Ruby: 694 nm (not used for hair removal anymore; not safe on most skin types)
• Alexandrite: 755 nm (most effective, but only safe on light skin)
• Pulsed diode array: 810 nm (for light to medium type skin)
• Nd:YAG: 1064 nm (for darker skin)

Pulsewidth is an important consideration. It has been observed in some published studies that longer pulsewidths may be safer for darker skin. However, shorter wavelengths are 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.

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
• 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, have been shown in numerous studies to provide long-term reduction of hair. Current parameters suggest a series of treatments spaced at 8-12 weeks apart for most areas, with face requiring shortest intervals and legs and back requiring longest intervals. These parameters are based on length of hair growth cycles on various areas.


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