Page 165 - Blog Posts v1

C1 - How strongly are different laser wavelengths absorbed in melanin and blood?
These days we use a wide variety of lasers and IPLs to treat various targets in the skin. Two major targets are hair and blood vessels. But how much of the laser/IPL light is actually absorbed by these targets?
Using data from two very clever scientists (Steve Jacques and Scott Prahl) it is relatively easy to calculate the absorption of a wide range of wavelengths in both melanin and oxyhaemoglobin.
Figure 1 shows the absorption curves for both of these chromophores across the visible part of the spectrum, up to 650nm. The red and blue curves show the absorptions for oxy- and deoxyhaemoglobin, respectively. Both chromophores absorb very strongly in the blue end of the spectrum (between 375 and 450nm) and then peak again between about 530 and 590nm. You might think that the blue end would be a better choice for skin treatments, but you'd be wrong! The problem with blue light is that it doesn't penetrate deep into the dermis very well!! So, we usually choose the 530 to 590nm range instead, which has much deeper penetration. These wavelngths can be generated by dye and KTP lasers and IPL units.
Figure 1: Absorption curves as found by Jacques and Prahl for melanin and haemoglobins
In the above diagram, the y-axis is a base 10 log scale - that means it jumps up by factors of 10s and 100s. This is done to display the curves at the lower end of the scale on the same picture as the very strongly absorbing portions. But, humans are not good at interpreting logarithmic scales, so I have created another picture to show the relations between these absorptions, more simply (I hope!).
The 'SC1' to 'SC6' curves in figure 1 represent the six major concentrations of melanin in the skin. SC1 epidermis has a melanin concentration of only 5% - very pale (commonly known as
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