For the first time, the possibility of a dual-stage active laser delivery of a modern chlorin-containing photodynamic preparation under the nail plate for photodynamic therapy of onychomycosis was investigated and demonstrated. The extinction spectra of the photodynamic preparation Revixan (Areal Ltd., Russia) were investigated at different temperatures, as well as before and after exposure to Er:YLF-laser radiation with a wavelength of 2810 nm and photodynamic LED radiation with a wavelength of 656 ± 10 nm. It is shown that after heating and laser exposure, the amount of monomers in the chlorin-containing photodynamic preparation increases, and after photodynamic exposure decreases, which can affect the effectiveness of photodynamic therapy of onychomycosis.