Page 46 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Figure 15 – 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 of 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 looks 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!!!)
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!
Many of these nerve endings are located just below the epidermal-dermal junction i.e. just below the skin surface (Error! Reference source not found.).
With photothermal treatments, the heat sensors can be triggered by heat flowing from the epidermal melanin and from heated tissues in the dermis.
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