## 2 Materials and Methods  
### Laser Source  
The radiation source consists of three individual diode laser emitters of type NDB7Y75 from Nichia (Nichia Corporation, Anan, Japan), which are arranged as a diode laser stack (Figure 2). Each individual diode laser emitter emits an output power of >4.5 W at a center wavelength of 455 nm. This results in 13.5 W full output power in CW mode. The arrangement of emitter stack, driver electronics, optics and fiber coupling was custom-made by A.R.C. Laser (A.R.C. Laser GmbH, Nuremberg, Germany) (Figure 3). The power regulation of the laser system for the CW and pulse operation modes was carried out by the so-called set point voltage (SPV) (voltage regulation), generated by the use of two Volt/Ampere meters, type MP710530 (MulticompPRO, Chicago, IL, USA). A function generator model AFG-2025 ([PERSON], New Taipei, Taiwan) was used to generate the laser pulses. This allows both the pulse repetition rate and the duty-cycle (DC) to be set individually. From the combination of pulse repetition rate f and DC, pulse durations \(\tau\) in the range from 1 \(\upmu\)s up to 900 ms were ultimately generated (Table 1). Mathematically, the relationships can be described as follows:  
\[\mathrm{DC}=\frac{\tau}{\mathrm{T}}=\tau\mathrm{\cdot f} \tag{1}\]  
\[\mathrm{P_{peak}}=\frac{\mathrm{P_{avg}}}{\mathrm{DC}}=\frac{\mathrm{P_{avg}} }{\tau\mathrm{\cdot f}} \tag{2}\]  
Figure 3: Setup of the experimental laser head. Figure 2: Arrangement of the diode laser emitter. where T is the pulse period, P\({}_{\rm avg}\) is average power and P\({}_{\rm peak}\) denotes peak power. The pulses generated with the function generator are emitted continuously without interruption if the laser is switched on. To generate defined pulse trains in the millisecond (ms) range, the continuously emitted pulse sequence is now systematically interrupted by the use of an additional custom-made pulse generator (A.R.C. Laser GmbH, Nuremberg, Germany). Figure 4 illustrates this situation. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & & & & & & & & & & & \\ \hline
10 kHz & 2 kHz & 1 kHz & 200 Hz & 133.3 Hz & 100 Hz & 66.7 Hz & 50 Hz & 40 Hz & 25 Hz & 1 Hz \\ (1 \(\mu\)s) & (5 \(\mu\)s) & (10 \(\mu\)s) & (50 \(\mu\)s) & (75 \(\mu\)s) & (100 \(\mu\)s) & (150 \(\mu\)s) & (200 \(\mu\)s) & (250 \(\mu\)s) & (400 \(\mu\)s) & (10 ms) \\ \hline  & & & & & & & & & & \\ \hline  & & & & & & & & & & \\ \hline
50 kHz & 10 kHz & 5 kHz & 1 kHz & 666.7 Hz & 500 Hz & 333.3 Hz & 250 Hz & 200 Hz & 125 Hz & 1 Hz \\ (1 \(\mu\)s) & (5 \(\mu\)s) & (10 \(\mu\)s) & (50 \(\mu\)s) & (75 \(\mu\)s) & (100 \(\mu\)s) & (150 \(\mu\)s) & (200 \(\mu\)s) & (250 \(\mu\)s) & (400 \(\mu\)s) & (50 ms) \\ \hline  & & & & & & & & & & \\ \hline
100 kHz & 20 kHz & 10 kHz & 2 kHz & 1.33 kHz & 1 kHz & 666.7 Hz & 500 Hz & 400 Hz & 250 Hz & 1 Hz \\ (1 \(\mu\)s) & (5 \(\mu\)s) & (10 \(\mu\)s) & (50 \(\mu\)s) & (75 \(\mu\)s) & (100 \(\mu\)s) & (150 \(\mu\)s) & (200 \(\mu\)s) & (250 \(\mu\)s) & (400 \(\mu\)s) & (100 ms) \\ \hline  & & & & & & & & & & \\ \hline
150 kHz & 30 kHz & 15 kHz & 3 kHz & 2 kHz & 1.5 kHz & 1 kHz & 750 Hz & 600 Hz & 375 Hz & 1 Hz \\ (1 \(\mu\)s) & (5 \(\mu\)s) & (10 \(\mu\)s) & (50 \(\mu\)s) & (75 \(\mu\)s) & (100 \(\mu\)s) & (150 \(\mu\)s) & (200 \(\mu\)s) & (250 \(\mu\)s) & (400 \(\mu\)s) & (150 ms) \\ \hline  & & & & & & & & & & \\ \hline  & & & & & & & & & & \\ \hline
200 kHz & 40 kHz & 20 kHz & 4 kHz & 2.67 kHz & 2 kHz & 1.33 kHz & 1 kHz & 800 Hz & 500 Hz & 1 Hz \\ (1 \(\mu\)s) & (5 \(\mu\)s) & (10 \(\mu\)s) & (50 \(\mu\)s) & (75 \(\mu\)s) & (100 \(\mu\)s) & (150 \(\mu\)s) & (200 \(\mu\)s) & (250 \(\mu\)s) & (400 \(\mu\)s) & (200 ms) \\ \hline  & & & & & & & & & & \\ \hline
250 kHz & 50 kHz & 25 kHzFor light transmission, step-index bare fibers with diameters of 283/300 \(\upmu\)m and 375/405 \(\upmu\)m (core/cladding) from heracle (heracle GmbH, Jena, Germany) were used. The usable wavelength range of these fibers is between 400 and 1000 nm with a numerical aperture (NA) of 0.22.