1. Fundamentals of Light and Laser Technology

Light is a form of electromagnetic radiation that behaves both as a wave and a particle (photon). It spans a spectrum of wavelengths, from high-energy gamma rays and X-rays to low-energy radio waves. The visible spectrum, which ranges from approximately 400 to 700 nanometers (nm), represents the portion of the electromagnetic spectrum detectable by the human eye. Each wavelength corresponds to a color, from violet (shorter wavelength) to red (longer wavelength). However, for many medical diagnostic applications, non-visible wavelengths, particularly near-infrared (NIR, 700–1400 nm) and ultraviolet (UV, <400 nm), are more effective due to their specific interactions with biological tissues (Barsom et al., 2016).

The interaction of light with matter, especially biological tissue, depends on properties such as absorption, scattering, reflection, and transmission. These interactions are influenced by the molecular composition and structure of tissues, and they vary with wavelength. For instance, near-infrared light is capable of penetrating several millimeters into tissue with minimal absorption, making it particularly useful for deep-tissue imaging and blood flow analysis (Zafar et al., 2021).