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Most laser-induced processes in the skin depend on the energy density - not just the energy. If a large spot size is used, say 10 mm, then the energy density may be too low to induce the desired reaction (500 mJ in a 10 mm spot diameter is only 0.6 J/cm2!!).
The easiest way to find the spot diameter is to 'burn' some paper - use a magazine with a dark page. The photo below shows some burns I have done with various lasers. Please note that the spot diameter usually increases as you 'turn up' the laser - this is simply because the laser is more efficient at higher energy levels.
So, in summary, when an energy is quoted for any skin treatment, the corresponding spot diameter should also be quoted. If you don't do that then you're only giving half of the
Mike’s Blog Posts 299
