Why CO2 Laser

The CO2 laser is the most adapted coetaneous thermal stimulator for heating the nociceptors up to their activation temperature.
Because the laser beam applies all the radiant energy exactly where the nociceptors are located in the superficial layers of the skin (located at +-100μm under the skin).

Then it increase the accuracy because of reduced energy diffusion.
It increase the security, since there is less danger to overheat deeper skin structures.
And there is less calorific energy needed because it is only deposited in the superficial skin layers.

All this, prevents any form of burning.

The penetration of electromagnetic radiation (e.g. RX, UV, IR, …) in the skin depends on the wavelength (λ) of that radiation. The greater the wavelength, the weaker the penetration in the skin. (Ref Hardy et al, Spectral transmittance and reflectance of excised human skin, J appl Physiol, 9 : 257-264, 1956).

For the CO2 laser, the wavelength is at 10.6 μm. At this wavelength, 99% of the power is deposited between 10 and 100μm since only 0.3% of the light emitted is reflected by the skin and that the transparency of the skin is weak (characteristic length = 10 to 60 μm). (Ref Bromm B, Treede RD, CO2 laser radiant heat pulses activate C nociceptors in man, Pfl ugers Arch, 1983 Oct ; 399(2):155-6.)

All this, prevents any form of burning.