2. Principles of Laser–Tissue Interaction

Scattering occurs when photons change direction due to interaction with tissue microstructures like cell membranes or organelles. The scattering coefficient depends on the wavelength and the heterogeneity of the tissue. Shorter wavelengths (e.g., blue light) scatter more, reducing imaging depth but improving resolution near the surface. Conversely, longer wavelengths (e.g., NIR) scatter less and penetrate deeper, albeit with reduced spatial resolution.

This tradeoff is a foundational design challenge in optical diagnostics. Technologies such as time-resolved spectroscopy, frequency-domain imaging, and multi-photon microscopy exploit scattering behavior to extract useful diagnostic signals from tissues at different depths (Barsom et al., 2016).