Page 90 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Now, if someone else was using a 4000W laser, also set to 25ms in a 2 cm2 spot size, then their laser will deliver 100 Joules in that pulsewidth (time). But, the fluence of this unit is 100/2 = 50 J/cm2.
So, a higher-powered laser will deliver more fluence in the same time (pulse) compared with a lower-powered laser.
Hence, we must be careful when comparing these lasers...
Triple Wavelength Diode Laser – what actually came out of it...
Triple wavelength diode lasers appeared on the market just a couple of years ago for hair removal. They claimed to enclose three sets of laser diodes emitting wavelengths at 755nm, 808 (or 810)nm and 1064nm.
The attached blurb (marketing) claimed that these three wavelengths generated a ‘better’ overall result when applied to unwanted hairs, simultaneously. As very sceptical physicists, we had our doubts....
Firstly, it seemed rather ‘convenient’ to me that the engineers had just happened to produce diode lasers which could emit the 755nm wavelength of the alexandrite laser and the 1064nm wavelength of the Nd:YAG laser – both of which have been used in hair removal for a number of years.
Secondly, the fluences that these triple wavelength devices would need to output would have to correlate to the absorption coefficients of melanin (the target in hair shafts). This is not a straightforward calculation without a pretty good understanding of the principles involved.
However, these issues are difficult to determine without a spectrophotometer to properly analyse what is really coming out of such a device. Our engineer colleague did precisely this analysis (Figure 32). He took a commercially available unit and plugged it into his measuring device. What he found was very interesting...
Firstly, the peak powers output by this unit did not coincide with the stated wavelength of 755, 810 and 1064nm. Instead, they were closer to 796, 817 and 1061nm – this was not surprising to us. We had always questioned these numbers!
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 11 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.
________________________________________________________________________ 90 Chapter 3 Laser/IPL Hair Removal
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