Laser superposition in multi-pass amplification process

Physical model was established to describe the pulse superposition in multi-pass amplification process when the pulse reflected from the cavity mirror and the front and the end of the pulse encountered. Theoretical analysis indicates that pulse superposition will consume more inversion population than that consumed without superposition. The standing wave field will be formed when the front and the end of the pulse is coherent overlapped. The inversion population density is spatial hole-burning by the standing wave field. The pulse gain and pulse are affected by superposition. Based on this physical model, three conditions, without superposition, coherent superposition and incoherent superposition were compared. This study will give instructions for high power solid laser design.