Physical Understanding of Laser Welding from a Quantum Mechanical Perspective

This work investigates the fundamental mechanisms of laser welding from a quantum mechanical perspective, focusing on microscopic interactions that are not fully explained by traditional thermodynamic or material-based models. Although photons have zero rest mass, they possess energy and momentum determined by their frequency and wavelength, enabling quantum-scale phenomena such as electronic transitions, lattice vibrations, ionization, and plasma formation. Based on Planck’s quantization, Einstein’s photon theory, and the principle of stimulated emission, this study explains how laser light is generated and how it interacts with metallic materials. Key factors such as electronic structure, wavelength-dependent absorption, and phonon-mediated energy transfer are examined to understand how energy propagates within metals during laser processing. In particular, the paper clarifies how photon energy is distributed between free electrons and the lattice, and how this leads to localized melting or plasma generation under specific conditions. These insights contribute to a more precise understanding of the physical principles behind laser welding and support improved control of energy delivery and material response in high-precision applications.