Page 91 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
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)
Absorption Coeff (cm-1)
755 - stated
164
796 - measured
137
810 - stated
128
817 - measured
125
1064 - stated
49
1061 - measured
50
Table 11 – 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.
The measured wavelengths varied from the stated wavelengths – this is to allow the marketeers to make claims based on proper clinical studies with alexandrite and Nd:YAG lasers. While the actual, measured wavelengths are not too far from their claimed values, it’s a bit ‘cheeky’!!
It would be very interesting to see the fluence outputs from some other systems to see if they account for the difference in melanin absorptions. If they don’t, then those systems may suffer from the same problem as the above device – a redundant wavelength! Most of the actual effectiveness will come from just the 755 and 810nm (or whatever they actually produce!)
________________________________________________________________________ 91 Chapter 3 Laser/IPL Hair Removal
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