Page 58 - Mike Murphy's Blog Posts

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.
Inside these electronic devices are usually found various electronic components including capacitors. These can store electrical charge until required. This is how peak powers can exceed average powers in these devices. By storing a certain amount of electrical energy, and then using it in a very short time, it is possible to generate large peak powers, which greatly exceed the average power – but only for a very brief time.
But there are limits on this. In the image above, if the average power indicated, is the maximum power that can be taken from the electrical supply system, then the maximum energy per pulse, pulsewidth and rep rate will all be tied together, by this limit.
If you wanted to increase the rep rate (more shots per second) then you would need to lower the maximum energy in each pulse – to allow for more shots with the same average
Mike’s Blog Posts 58