## 2 Materials and Methods
### Testing Procedure  
The experimental procedure was conducted on a vibration-free optical table at a stable room temperature of 18 \({}^{\circ}\)C, at the Laser Laboratory of the Institute for Plasma Physics and Lasers of the Hellenic Mediterranean University of Rethymno, Greece. The experimental set-up and the different optical elements used for performing the spectral measurements are indicated in Figure 1. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Photosensitizers** & **Brand** & **Concentration** & **Laser Wavelength** & **Power Output** & **Tip Diameter** \\  & **Name/Manufacturer** & **(mg/mL)** & **(nm)** & **(mW)** & **(mm)** \\ \hline \multirow{3}{*}{Curcumin} & Ultracur+Pro\({}^{\otimes}\), Weber & & & & \\  & Medical GmbH, & 5 & 445 & 150 & 6 \\  & Lauenförde, Germany & & & & \\ \hline \multirow{3}{*}{Methylene blue} & Methylene Blue, & & & & \\  & Sigma-Aldrich Merck & & & & \\  & KGaA, Darmstadt, & 0.05 & 660 & 150 & 6 \\  & Germany & & & & \\ \hline \multirow{3}{*}{Methylene blue} & Methylene Blue, & & & & \\  & Sigma-Aldrich Merck & & & & \\  & KGaA, Darmstadt, & 0.10 & 660 & 150 & 6 \\  & Germany & & & & \\ \hline \multirow{3}{*}{Methylene blue} & Methylene Blue, & & & & \\  & Sigma-Aldrich Merck & & & & \\  & KGaA, Darmstadt, & & & & \\  & Germany & & & & \\ \hline \multirow{3}{*}{Methylene blue} & Photolase\({}^{\otimes}\), Europe Ltd., & & & & \\  & Hamburg, Germany & & & & \\ \hline \multirow{3}{*}{Methylene blue} & Photolase\({}^{\otimes}\) Europe Ltd., & & & & \\  & Hamburg, Germany & & & & \\ \hline \multirow{3}{*}{Toluidine blue} & BluLase PDT Gel, & & & & \\  & Schneider-Dental, Plisach & & & & \\  & Germany & & & & \\ \hline \multirow{3}{*}{Toluidine blue} & BluLase PDT Gel, & & & & \\  & Schneider-Dental, Plisach & & & & \\  & Schneider-Dental, Plisach & & & & \\  & Germany & & & & \\ \hline \multirow{3}{*}{Indocyanine green} & Emundo\({}^{\otimes}\), A.R.C. laser & & & & \\  & GmbH, Nurnberg, & 0.10 & 808 & 150 & 6 \\  & Germany & & & & \\ \hline \multirow{3}{*}{Indocyanine green} & Emundo\({}^{\otimes}\), A.R.C. laser & & & & \\ \cline{1-1}  & GmbH, Nurnberg, & 1.00 & 808 & 150 & 6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Photosensitizers and their respective manufacturers, concentrations and laser parameters applied in the experiments conducted. In order to achieve a uniform area of thickness for each component, a 1 mm layer of thickness quartz glass cuvette was applied (Hellma Macro-cuvette 100-QX, Hellma GmbH, Mullheim, Germany). A new and clear cuvette was used for each photosensitizer in order to ensure its transparency. All photosensizers examined were freshly mixed prior to implementation of the analysis. After attenuating the intensity from the laser source (LS), the central part of the output was selected by an iris diaphragm (I), which controlled the intensity, shape and divergence of the beam to interact with the examined sample. The light beam was focused with a biconvex lens (F) of a focal length of f = 15 cm. To avoid undesired scattering, a mask was applied before light reached the sample. As noted above, the sample holder was a specially designed cuvette, which contained the photosensitizer at a spatially uniform thickness of 1 mm, since this is a previously described optimal path length for spectrophotometric studies that allows accurate measurements [30]. After passing through the cuvette, the light pathway was further controlled with another mask. Prior to reaching the sensor fibre, the light intensity was moderated if needed, with different attenuator filters. Finally, the transmitted beam was directed to the optical sensor fibre (QP100-2-VIS-BX, Ocean Optics, Largo, FL, USA), which was connected to a high-resolution spectrophotometer (HR4000 CG-UV-NIR, Ocean Optics, Largo, FL, USA). The spectrophotometer monitored absorbance within the wavelength range of 400-1000 nm. For every measurement made, a reference transmission spectrum was recorded for each laser wavelength without any photosensitizer, i.e., for the cuvette alone.