Page 61 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Figure 24 – Controlled skin cooling techniques
Unfortunately, many IPL and diode laser manufacturers claim that that their waveguides are
made of sapphire while they instead use optical glass such as quartz glass. There is a huge difference between sapphire and optical glass in terms of heat conductivity that has an enormous impact on the cooling efficiency. The thermal conductivity of sapphire is about 30 times higher compared to any type of optical glass. For the naked eye sapphire and optical glass look the same. The easiest way to distinguish sapphire from glass is to make a scratch test with sharp a tipped metal piece such as a knife, screwdriver. As sapphire is the second hardest material after diamond you would not be able to scratch that with any type of metal while glass easily can be scratched with sharp piece of hard metal. (WARNING – this may damage your tip if it is not sapphire!!!).
The essence of good skin (dermal) cooling is applying a very low temperature to the skin surface for the required time. This is where ice-pack cooling wins, every time. As long as the ice is frozen, i.e. at 0C, and it is applied for at least two minutes prior to the light energy, then the dermis will be suitable cold down to 4 mm deep, or so. Just as we need to apply heat for the correct length of time to ensure a good result, we must also apply cooling, at the right temperature, for the right time, to ensure proper cooling.
Thermal Pain Sensors
The dermis contains a range of nerve endings which can respond to heat, cold, pressure and pain. Incidentally, there are four times as many cold sensors as there are heat sensors!
________________________________________________________________________ 61 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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