Figure 1. Physical experiments: Laser irradiation of the cadaver skin sample.

a. A schematic diagram of the experimental setup to detect the mechanical impact of laser on the cadaver skin sample. The frequency-doubled Q-switched pulsed laser (5 ns pulse width) was used to generate a single-shot laser beam at a 532 nm wavelength. The generated beam was adjusted to focus on the skin sample through an optical filter and a lens. The spot size of the beam on the skin sample was 0.48 mm. The cadaver skin sample was attached to the front side of a PVDF transducer. Eight different beam energies used in the experiment ranged from 0.12 to 1.90 mJ, remaining under the MPE level to ensure no biological damage to the skin sample. b. The time series of the PVDF transducer sensor output signals recorded from 20 ms before to 400 ms after stimulation are represented in terms of voltage [V] along the left vertical axis and pressure [MPa] along the right vertical axis, respectively. Complex patterns of mechanical waves were consistently observed for eight different beam energy levels. The first negative peaks (~5 ms after stimulation) were generated by stress waves arriving at the sensor. The subsequent complex waveforms were attributed to the dynamic of the sensor and the measurement setup. c. Pressure values measured at the first negative peaks generated from the different beam energy levels. The open circles denote the average pressure values and the vertical bars denote the standard deviation. The maximum pressures were 0.68 ± 0.02 MPa generated by the highest beam energy (1.90 mJ). The pressure values were linearly correlated with the beam energy levels (r² = 0.9969, the slope of the linear regression model = 0.35 MPa/mJ). (Fig. 1 was obtained from Konkuk University, drawn by MATLAB and MS power point software and created by Jae-Hoon Jun).