Page 259 - Blog Posts v1

E25 - Triple Wavelength Diode Lasers
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 a very sceptical physicist, I had my 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. Hmmm....
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.
My engineer colleague did precisely this analysis. He took a commercially available unit and plugged it into his measuring device. What he found is 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 me. I 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?
Wavelength (nm)
Absorption Coeff (cm-1)
755 - stated
164
796 - measured
137
810 - stated
128
817 - measured
125
Mike’s Blog Posts 259