Page 171 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Body area
Threshold fluence (J/cm2)
Upper lip
11.5
Chin/arms
20.8
Arm pits/legs
23.9
Bikini
27.9
Table 29 - Threshold fluences for IPLs
It must be understood that a small increase in fluence results in a small increase in temperature in the stem cells, but that the rate of denaturation increases exponentially with temperature. So, even a 1oC rise in temperature in those cells will have a very significant effect on the outcome!
Diode Laser – Threshold fluences
The diode laser wavelengths (808, 810nm) are very similar to the averaged output from an IPL (with a Xenon lamp). As a direct consequence, the threshold fluences are also very similar.
The threshold at the skin surface for diode lasers (at 810nm) is approximately 11.1 J/cm2, assuming a 10ms pulsewidth. The 808nm laser will be very slightly different.
Body area
Threshold fluence (J/cm2)
Upper lip
11.1
Chin/arms
20.3
Arm pits/legs
23.2
Bikini
27.2
Table 30 - Threshold fluences for diode lasers
Diode systems come in a range of maximum output powers. Some units can deliver up to 500 Watts, while others might go as high as 5000 Watts (claimed optical power output!) with different spot sizes. This means that they deliver their energy at different rates – so a 5000W laser will deliver its energy 10 times ‘faster’ than a 500W laser. But fluence doesn’t depend on this at all – when we consider the delivery rate, we are discussing power density (or ‘intensity’/’irradiance’ in proper physics parlance).
So, if the fluence from a 500W laser is 10 J/cm2, then a 10 J/cm2 from a 5000W laser is precisely the same – however, the 5000W laser will deliver this fluence in a pulsewidth equal to one tenth of the pulsewidth from a 500W laser.
________________________________________________________________________ 171 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
© The Laser-IPL Guys, 2025