Classical physics has long assumed that free photons carry intrinsic momentum inherently, which is used to interpret optical phenomena including light pressure, laser cooling and the photoelectric effect. However, the fundamental definition of momentum P=mv leads to an unavoidable logical contradiction: momentum is inseparable from mass. If photons have intrinsic momentum, they must possess inherent mass, conflicting with the well-established property that free photons travel constantly at the speed of light in vacuum with zero rest mass, forming an irreparable foundational flaw in conventional physical frameworks. Combining the complete intrinsic properties of photons, this paper establishes a new physical picture based on the mechanism that trapped radiant light energy converts into tangible mass. A free photon solely consists of pure radiant energy without substantial mass or innate momentum. All momentum-related effects observed in optical experiments emerge as apparent secondary momentum after photons are captured and confined by matter, with trapped radiant energy solidifying into physical mass that inherits the original moving direction of incident photons. Once light energy transforms into material mass, photons cease traveling at the speed of light immediately, and the final velocity of newly generated particles is determined by the overall energy gain and loss throughout the confinement process. Velocity alteration caused by single-photon capture is extremely negligible, and macroscopic outcomes such as laser cooling and laser-driven atomic acceleration arise from cumulative confinement and repeated energy exchange of massive quantities of photons. All classic physical formulas including Einstein’s \(E^2=(pc)^2+(m_0c^2)^2\), the photon momentum formula P=E/c and relativistic dynamic mass equations remain mathematically valid without denial in this article; this work only redefines their applicable scope. Supported by landmark laser cooling experiments completed by Steven Chu and William D. Phillips featuring opposite and co-directional laser incidence, this paper corrects the long-standing misunderstanding of photon momentum and elaborates the fundamental interaction principle between light and matter under a unified physical mechanism.