I’m a physicist, so I know something about how to look at these numbers being batted around. There’s a great paper at http://www.aesthetic.lumenis.com/pdf/laser_principles_aspects.pdf that talks about the requirements needed to effect permanent hair removal.
Basically, here’s my analysis: The Tria will probably effect permanent hair removal for SOME people, and not for most.
The best candidates will be those with very course, very dark hair, I’m guessing on the lowest setting. Here’s why:
The total energy absorbed by a single hair follicle is a function of: laser energy output, pulse duration, and, very importantly, the ratio of pigment concentration in the root area to the skin.
The emitted photons are only absorbed by melanin, and the more melanin there is at the root, the higher the percentage of photons are absorbed in the right place. Also, the larger the hair is, the more volume is available to absorb photons. (Because of the quantum mechanical nature of light, not all of the photons will be absorbed exactly at the surface… some will be absorbed inside, and some will pass right through.) The hair will absorb light so readily, I’m guessing higher levels may get too hot and damage the skin.
The rate of heat dissipation is dependent upon the size of the hair, which effects the rate of thermal transfer. The larger the hair is, the faster energy is dissipated, but the higher a heat capacity it will have. Heat capacity (goes as the square of radius) goes up much faster than transfer rate (which increases linearly with radius), so the net effect will be that the heat will be better retained.
The specs of the TRIA are on the outside edge of the those used by other professional systems. For the right person: someone who tans easily and has course hair (I’m thinking, for example, of Asians), the Tria might work a charm. Even though the number of joules per cm^2 is low, the high melanin concentration will make up for that. Their skin is light enough the ratio is huge. Even though the pulse width is high, the large hair size will hold the heat.
On the other hand, anyone who has relatively fine hair, or anything other than jet black hair, probably won’t see permanent hair removal.
One thing that may help: using a depilatory cream after shaving to eat down the hair as far as possible will reduce the amount of laser energy absorbed outside the root. This may also help reduce damage to the surrounding tissue. (This is mentioned as an alternative to shaving in the paper.) It also reduces the surface area through which heat can be dissipated. You might even be able to turn up the intensity another notch without causing injury.
So if you are asian, or perhaps a light skinned black person, this might work out for you. If you are Norwegian, on the other hand, probably not so much.
Last, and I say this only as a rather crazy person, and you would NEVER EVER do this yourself because you don’t know how to do it right and because you are not sufficiently an expert in this subject to even dare attempt such a thing – RIGHT??? – I bet good money I could modify the device to perform just as well as a commercial system by shortening the pulse duration and lensing the light onto an area with a diameter that is 1/sqrt(2)=.7 times the diameter size of the current spot. That would halve the spot size, double the number of joules/cm^2, and, to compensate, the pulse need to be halved to 60ms. Of course, this would void all warranties, void the FDA approval, and would be very, very, very stupid for anyone to try without a experts understanding of optics and a daredevil willingness to accept the risks. But it would work.
