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E30 - BMLA Presentations 2019
I’ve just been confirmed for two talks at this year’s British Medical Laser Association meeting in London in May. I’ll be presenting OP18 and OP20 on Friday May 10th, 2019 at 8.15am and 8.45am respectively, in the Endeavour Room.
1st Presentation – OP18
The first presentation is entitled “Laser Tattoo Removal – a deeper analysis of the various processes.”
In this talk I will be presenting my recent work on the range of physical processes which occur during the laser heating processes which can occur including micro-cavitation, explosive boiling, the carbon steam reaction, fragmentation, the photo-acoustic reaction and photospallation.
All of these processes are temperature dependent (which, in turn, depends on the incident intensity and wavelength). As the absorbing ink particles rapidly rise in temperature, different physical processes occur with increasing ‘ferocity’.
At the ‘spinodal’ temperature of water - 277C – the water boils rapidly resulting in the formation of steam bubbles around the ink particles. As these bubbles collapse they release energy back into the ink particles resulting in micro-cavitation. At around 299C the boiling of water becomes explosive which generates rapidly expanding steam vacuoles.
Ink particles will begin to physically fragment at these temperature with some particles leaving the skin at very high speeds (photospallation) – some exceeding the speed of sound!
At 705C the carbon-steam reaction begins; where carbon molecules, in a water medium, undergo a chemical reaction resulting in the production of hydrogen and carbon monoxide gases. This is particularly noticeable with black pigment since they are usually composed of carbon.
Photoacoustic effects occur when the absorbed energy induces temperatures over one thousand degrees Celsius on the surface of the ink particles. If the pulsewidth is on the order of the stress confinement time (related to the speed of sound in the ink particles) then acoustic waves are formed which propagate within the ink particles. These waves produce resonating forces within the ink which can exceed the molecular bond strength of the particles, leading to fragmentation.
Finally, at around 3685C carbon particles will undergo sublimation – the phase change from solid directly into a gas (it does not pass through a liquid phase under this process). At this stage the solid carbon particles are no longer present.
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