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So, we can see that a higher powered laser will deliver more fluence to the skin in the same time (pulsewidth) than a lower powered laser. This means that the temperature rise in the target hair will be higher – simple because a higher fluence results in higher temperatures.
If the same fluence is delivered to the skin using a longer pulsewidth (say 40ms instead of 20ms), then the resulting temperature will be lower because more of the heat energy will have conducted away from the hair during the pulse!
This all makes it a bit tricky when comparing diode lasers of different powers. A 20J/cm2 fluence from a 1000W will generate a lower maximum temperature in the hair compared with a 20J/cm2 fluence from a 5000W laser – because the 5000W laser will deliver the energy much faster!
Repetition Rate
The repetition rate is the ‘number of shots per second’ that are fired to the skin. It is usually measure in Hertz (Hz).
In many diode lasers, increasing the repetition rate also alters the fluence/pulsewidths too – usually by lowering these values!!! So you might have to ‘compromise’ between repetition rate, fluence and pulsewidth to achieve a good result.
When applying the ‘stamping technique always use the 1Hz setting – that will allow you to fire a single shot with ease.
For the SHR, gliding, dynamic mode, use higher repetition rates – between 5 and 10 Hz.
Combination...
In reality, the three main settings – fluence, pulsewidth and repetition rate – are often “tied” in many diode laser systems. This means that when any one of these settings is changed, the one, or both, of the other settings also change.
So, if you want to increase your fluence, then the pulsewidth will also increase – to allow more energy to be output. But, the repetition rate might fall. This is simply because the laser has a fixed limit in terms of it maximum output – it just cannot go above a certain level.
Likewise, if you want to fire more shots per second at the skin (higher repetition rate) then, quite often, the fluence will drop!
Mike’s Blog Posts 280