2. Principles of Laser–Tissue Interaction

In laser–tissue interaction, energy level plays a defining role in determining whether the effect is diagnostic or therapeutic. Diagnostic applications require low-energy, non-destructive interactions that provide optical signals without damaging cells or tissue. These signals might include:

• Elastic scattering, used in diffuse reflectance and OCT;
• Fluorescence, used in LIF for metabolic or cancer detection;
• Raman scattering, used to identify molecular compositions via inelastic photon shift.

In contrast, therapeutic effects such as photocoagulation, ablation, or photomechanical disruption occur at higher energy levels and often rely on thermal or mechanical changes in the tissue (Zafar et al., 2021).