Page 208 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
If you deliver exactly the same energy over 2 ms, then the peak power becomes 10/0.002 = 5000 Watts.
Did you spot the word “peak”?
This is very important when discussing power. And this is where some laser suppliers are trying
to pull the wool over your eyes...
The ‘peak’ power is the maximum possible power that might be generated in a laser pulse. It is a specific measurement – maximum energy divided by the pulsewidth. And this becomes a bit trickier when you need to define precisely how you measure the pulsewidth!!
Peak power
Figure 112 - Peak power versus average power
In the image above, we can see three individual laser pulses (they could be IPL too – it doesn’t matter). The peak power could be found by dividing the maximum energy in each pulse by the pulsewidth (here it is measured at the ‘midpoint’ where the power is exactly half the maximum value – we call this the FWHM value.)
However, as you can see in the image, the ‘average power’ is significantly lower than the peak power. The ‘average power’ is defined as ‘total energy’ divided by the ‘total time’. Clearly, the total time, in the image, is much greater than the pulsewidth, so the average power is bound to be much lower. (Incidentally, the ‘rep rate’ is the number of pulses per second, usually measured in Hertz (Hz)).
Now, in electronic systems, such as lasers and IPLs, the maximum available average power is essentially determined by the electrical power drawn from the wall socket. That supply can only deliver a certain amount of power, which is determined by the electrical supply to that building.
________________________________________________________________________ 208 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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