ISSN (web): 1855-9921
High-Temperature Triggering of Soft-Tissue Regeneration by Er:YAG Laser
Nejc Lukac, Blaz Tasic Muc, Matjaz Lukac
In Er:YAG laser (λ = 2940 nm) procedures, it is the tissue’s water content, not its pigment, that plays the role of an absorbing chromophore. Therefore, the temperature elevation ΔT is not laser-induced at locations of particular pigments, such as melanin or hemoglobin, but is limited to the superficially irradiated tissue layer, with the irradiation thickness determined by the laser’s extremely short optical penetration depth (δ).
During pulsed laser procedures, the resulting temperature pulse consists of the temperature ramp-up heating phase, during which the temperature reaches its maximal value (Tmax), and of the cooling phase, during which the temperature returns back to its initial temperature T0. The heating phase lasts for the duration of the laser intensity pulse (tp), while the cooling phase is determined predominantly by the rate of the heat flow away from the heated superficial tissue. Here, Er:YAG is at a significant advantage since, due to its highest absorption in tissue water, the temperature decay time td ≈ δ2/D is extremely short (D is the tissue’s thermal diffusivity).
In this paper, we report on a measurement of the thermal pulse as induced by a short Er:YAG laser pulse (tp = 0.3 ms) on the patient’s skin. A special high-speed thermal camera (FLIR A6750 SLS, manufactured by FLIR Systems, USA) at a fast frame rate of 4000 Hz was used to detect the extremely fast temperature evolution during and following a single Er:YAG laser pulse generated by a Dynamis SP laser system equipped with a 5-mm full-beam R11 handpiece (both manufactured by Fotona d.o.o., Slovenia). The laser pulse fluence of Fp = 0.8 J/cm2 was set to be just below the ablation threshold Fabl ≈ 0.9 J/cm2.