Page 213 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
The next interesting observation was that the peak powers emitted at the 796 and 817nm were almost identical, but both were around 2.5 times more powerful than the 1061nm wavelength.
What does this mean in terms of treatments?
Table 39 shows the various absorption coefficients of melanin at the claimed and measured wavelengths. These determine how much of the light energy may be absorbed by the hairs.
The differences between the 810/817 and 1064/1061nm wavelengths are minimal, while the difference between 755 and 796nm is around 27cm-1 which is not insignificant.
Wavelength (nm)
Coeff (cm-1)
755 - stated
164
796 - measured
137
810 - stated
128
817 - measured
125
1064 - stated
49
1061 - measured
50
Table 39 – The melanin absorption coefficients for the measured and stated wavelengths
However, the important issue here is the relative absorption across these three wavelengths. The 796 and 817nm wavelengths absorb almost at the same ‘rate’ (with coefficients of 137 and 125 cm-1), but the 1061nm wavelength absorbs much more poorly, with a coefficient of only around 50cm-1. This means that the first two wavelengths will absorb about 2.6 times more strongly than the 1061nm wavelength!
Remembering that the 1061nm has only about 1/2.5 times the output power of the other two wavelengths, means that if these diodes are all set to output the same fluence, then the 1061nm wavelength will be around 1/(2.5 x 2.6) times heating effect on the melanin – this is only 15% of the effectiveness of the 796 and 817nm wavelengths.
Essentially, this means that the 1061nm is pretty useless in this treatment!! At this level of heat generation it will have virtually no effect on the cells.
Conclusion
The spectrophotometer analysis of a real-world, triple-wavelength diode system has revealed that the 1064nm (1061nm - measured) wavelength is effectively redundant! It cannot actually do much, if all the output fluences across the diodes are equal.
________________________________________________________________________ 213 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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Absorption