Ray-based method, paraxial Gaussian beam and physical light propagation. According to the related data of Gaussian pop, the pop in Gaussian is based on the mode of light, the propagation of paraxial Gaussian beam and physical light. The ray-based method uses geometric ray tracing to simulate beam propagation. Paraxial Gaussian beam calculates all kinds of beam data when Gaussian beam propagates through paraxial optical system, including beam size and beam waist position. POP simulates laser beams by propagating coherent waves, and can study arbitrary coherent beams in detail.