Page 147 - Mike Murphy's Blog Posts

So, even though the white paper is reflecting most of the laser energy, the crack sound is still generated.
But that’s because the crack has nothing to do with the surface!!!
So, don’t “chase the crack” - it will not help the treatment and could end up creating unwanted damage due to excessive fluencies!
ADDITIONAL - ADDED 24 JULY 2021
To 'enhance' the above argument I made a couple of videos using a QS Nd:YAG laser on my wife's arm. She did agree, but only after much enticement and some bribes...
https://videopress.com/v/QBs7wN9C?resizeToParent=true&cover=true&preloadContent=m etadata
Here I used a 1064nm wavelength set to a small 1 mm spot diameter. This results in an applied fluence of around 60 J/cm2. My wife has no tattoos (yet!) so this laser energy is being applied to 'normal', tanned skin - it has a relatively high melanin content at the moment due to the excess sun radiation we have been subjected to recently!
You can clearly hear the 'cracking' sound whilst virtually zero reaction is seen on the skin, even with the high melanin levels. The 1064nm wavelength is very poorly absorbed by melanin so there is little reaction there. But, the excessively high fluence is generating the cracking sound - even with no real absorption in the skin!
https://videopress.com/v/JcoWRzwM?resizeToParent=true&cover=true&preloadContent= metadata
In this video I apply a 532nm wavelength in a 1 mm spot diameter, again at around 60 J/cm2. This time, the melanin reacts to the laser energy and 'balloons' as it explodes resulting in local steam formation - commonly known as 'frosting'.
You can also hear a significant cracking sound here, because the fluence is so high...
The fact is, the cracking sound is generated purely due to the high fluences often used erroneously by laser users. It does not add to the treatment outcome, but can lead to skin damage.
Ciao for now, Mike.
Mike’s Blog Posts 147