Page 205 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
If that energy is delivered in a very short time (like a few nanoseconds – billionths of a second) then there is no time for that heat to escape into the surrounding tissues while the light is still being delivered. This is a ‘high power’ situation – the energy is being delivered quickly.
If the same energy is delivered in a much longer pulse – say, a few milliseconds – then there is plenty of time for heat to ‘leak out’ of the absorbing target during the pulse. This means there is heat escaping while more heat is still being generated by the incoming light. As a consequence, the local temperature is not as high as with the ‘high power’ situation – simply because some of the heat energy has been lost to the adjacent tissues. This is a ‘low power’ situation.
So, how does this relate to diode laser systems?
Figure 111 - A simple diode laser array
Diode Lasers
The diode lasers we use in aesthetic treatments are usually comprised of an array of little diode lasers (see Figure 111). Each diode laser delivers a small amount of power, so they must be stacked up into an array to produce sufficient energy for our needs.
An individual array of diodes might generate an overall optical power of 1000 Watts. If we put that into a handheld device, we would then have a 1000W diode laser, with a spot size equal to the area of the array. This might be 1 cm2.
So, this 1000W array can deliver 1000 Joules of energy in 1 second (that’s the definition of ‘power’ – energy per second). This would be delivered in a 1 cm2 area. This means that this particular device can deliver a fluence of 1000 J/cm2 in 1 second.
But that’s way too much energy/fluence for our requirements. Typically, hair removal requires something like 20 to 50 J/cm2 to kill the follicles.
Here is where things get interesting...
________________________________________________________________________ 205 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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