COMPUTATIONAL MODELS FOR LASER RADIATION AMPLIFICATION IN ACTIVE MEDIUM OF IODINE LASER

V.A. Yeroshenko, A.V. Kondrashenko
VANT. Ser.: Mat. Mod. Fiz. Proc 1997. Вып.1. С. 67-68.

      Computations for short pulse amplification in active medium with degenerate laser levels (such medium is atomic iodine) often use quasi-classical model which is an extension by analogy of equations for a nondegenerate two-level system. For each permitted transition its own polarization is therewith introduced, while the inverse population is written with account of statistic, weights of the degenerate levels. This model is not quite consistent and computations on its base sometimes yield physically senseless results (negative level populations). A consistent model should be based on equations for a complete density matrix. For the iodine atom this matrix is of 36 x 36 dimension.
      This work studies effects relating to transition from the complete model to the two-level level-degenerate model using a model three-level system with the degenerate lower level as an example. These studies showed that for a pronounced coherent mode only the complete model provides physically proper results. At the same time, when intrusion in the coherent region is not very deep, the two-level approximation yields very good results.
      In the experiments on powerful iodine laser facilities “Iskra-4” and “Iskra-5” in some, cases pulse duration is on the order of the phase relaxation time. Thus, at least to control computation accuracy, as well as in order to be able to compute laser pulse amplification with constant magnetic field present, it is desirable to have the laser pulse amplification model based on the complete iodine atom density matrix of 36 x 36 dimension. This model was implemented in the ZSK program.