Page 179 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
All of these systems can produce good results but their use depends on a good understanding of the fluence and pulsewidth necessary to kill the germ cells.
Long-pulsed alexandrite Lasers:
Long-pulse alexandrite lasers have been used for hair removal since around the mid 1990s, with a high degree of success on paler skins. These systems appear to be more popular in America than in Europe.
Typically, they output fluences up to around 50 J/cm2 in pulsewidths in the range 2 to 20 ms, yielding a power density range between 2,500 and 25,000 W/cm2, in a 755nm wavelength. The very high power density is due to some systems generating very high fluences in short pulses – however, these are likely to be rarely used in a real-world setting.
Long-pulsed Nd:YAG Lasers:
Typically, these lasers use pulsewidths in the range 10 to 40 ms, with fluences between 30 and 60 J/cm2. A major UK supplier offers a system with up to 45 Joules per pulse in 10 ms pulsewidths, with repetition rates of 1 and 2 Hz. This device can clear hair follicles very successfully. Hence, they can generate power density outputs between 3000 and 6000 W/cm2 in each pulse, in a wavelength of 1064nm.
Long-pulsed Nd:YAG lasers have been used for hair removal for around 30 years. Their main advantage is that their low absorption in melanin means that they are much less likely to damage the epidermis. However, the absorption in follicle melanin is much more significant compared with the epidermal melanin (due to the higher concentration), Hence, it can be successfully used to target and damage follicle.
While Nd:YAG lasers are usually quoted as ‘useful’ for darker skin colours, they are, in fact, very good for all skin colours!
It appears obvious from Table 41 that there is a wide range of power densities, all of which can generate good results – a range from 200 to 6000 W/cm2. At first sight, this seems odd! How can such a large range of power densities all generate similar results?
Well, it must be remembered that the power density combines the fluence with the pulsewidth, and the numbers in Table 41 represent a wide ‘mix’ of these two important settings. Remember, there is more than one way to boil an egg...
________________________________________________________________________ 179 Chapter 3 Laser/IPL Hair Removal
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