Four-level generation in Laser-Induced Plasma Lasers

This study examines the performance of Laser-Induced Plasma Lasers (LIPLs) using a four-level generation system. Population inversion, necessary for laser operation, is achieved mostly, through collisional transitions from the pumped level. The research highlights that direct collisions, which skip intermediate levels, are more efficient at achieving population inversion than multi-step cascade processes. When the energy gap between the pumped and upper-generation levels is very small (≤0.1 eV), these levels effectively merge into a single state, creating a quasi-direct generation (QDG) scheme. This QDG scheme often follows the same polarization rules as the direct generation (DG) scheme.