Following my post yesterday re laser power, I thought I’d explain further using the medium of video…
The above shows a Q-switched Nd:YAG laser outputting pulses of energy 0.3 Joules in 10 nanoseoncd pulsewidths. These equate to a peak power of 30 million Watts in each pulse (30 MW).
However, the ‘peak’ power relates to the individual pulsewidths for each pulse. The ‘average’ power relates to the total time over which these pulses are delivered. So, if we fire these pulses at 10 Hz (10 shots every second), then the total energy delivered in one second is 10 times 0.3 Joules. The average power is simply the total energy divided by the total time – 3 Joules / 1 second, which is only 3 Watts.
We can see a big difference between firing these pulses at photo paper and at the tangerine skin. That’s simply becasue the photo paper absorbs much more of the laser energy than the tangerine does.
This example shows the massive difference between average and peak powers – they are NOT equivalent.
In the video above, we can see that the laser pulses have very little effect on the tangerine skin, even though the peak power in each pulse is huge.
Now let’s look at a carbon dioxide laser. In this video I set the laser to a 10 Watt output. We can see it has a much more impressive effect on the tangerine skin – it vapourises is very easily.
In this situation, the CO2 laser is outputting 10 Watts “continuously” – these are not pulses. So this laser is delviering 10 Joules of energy in every second, continuously.
Conclusion
We can clearly see from the above videos that there is a massive difference between average and peak powers – they are two completely different things. They should not be confused. As I mentioned in yesterday’s post, it is important to understand this difference when considering the purchase of a laser.
Do not be duped into thinking that a stated (or claimed) power is the ‘average’, when it is clearly the ‘peak’ power. And this may, or may not, have much effect in skin treatments…
Hope this all helps a bit,
Mike.
Mike Murphy's Blog 