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Comparing different wavelength lasers with 808nm diode laser hair removal
Jul 31, 2018

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

Laser UsedWavelength (nm)Light SourceType of Skin used on
Argon488 nm or 514.5 nmTurquoise/Cyan or GreenNo longer used
Ruby694.3 nmDeep redPale
Alexandrite755 nmNear-infraredAll skin types
Pulsed diode array810 nmNear-infraredPale to medium
Nd:YAG1064 nmInfraredDarker complexion
Intense pulsed light (IPL is not a laser)650 nmNot a laserPale to medium


Hair-removal laser working at 755nm and 1064 nm. The device to the right provides air cooling.

Pulse width (or duration) is one of the most important considerations. The length of the heating pulse relates directly to the damage achieved in the follicle. When attempting to destroy hair follicles the main target is the germ cells which live on the surface of the hair shaft. Light energy is absorbed by the melanin within the hair and heat is generated. The heat then conducts out towards the germ cells. As long as a sufficient temperature is maintained for the required time then these cells will be successfully destroyed. This is absolutely critical – attaining the required temperature is not sufficient unless it is kept at that temperature for the corresponding time. This is determined by the Arrhenius Rate Equation. To achieve these conditions the laser/IPL system must be able to generate the required power output. The main reason why hair removal fails is simply because the equipment cannot generate the desired temperature for the correct time.

Fluence or energy density 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 heat up the follicles enough to disable them from producing hair.

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

  • Contact cooling: through a window cooled by circulating water or other internal coolant. This type of cooling is by far the most efficient method of keeping the epidermis protected since it provides a constant heat sink at the skin surface. Sapphire windows are much more conductive than quartz.

  • Cryogen spray: sprayed directly onto the skin immediately before and/or after the laser pulse

  • Air cooling: forced cold air at -34 °C

Spot size, or the width of the laser beam, directly affects the depth of penetration of the light energy due to scattering effects in the dermal layer. Larger beam diameters or those devices that has a linear scanning results in deeper deposition of energy and hence can induce higher temperatures in deeper follicles. Hair removal lasers have a spot size about the size of a fingertip (3–18mm).

In essence, the important output parameter when treating hair (and other skin conditions) is power density – this is a combination of energy, spot diameter and pulse duration. These three parameters determine what actually happens when the light energy is absorbed by the tissue chromophore be it melanin, hemoglobin or water, with the amount of tissue damaged being determined by the temperature/time combination.


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