Investigation of the gain anomaly of lithiumlike ion 3d-4f and 3d-5f lasers in a recombining silicon plasma

We report an experimental investigation of the gain anomaly of lithiumlike 3d - 4f and 3d - 5f lasers in a recombining silicon plasma. We examined the spatial distribution of gain coefficients of the two lasing lines and foun d that the peak gain of the 3d - 5f laser occurs closer to the target surfa ce than that of the 3d-4f laser, which is contrary to the results predicted by simulation. This discrepancy, which to our knowledge was not pointed ou t before, was found to be relevant to the gain anomaly of lithiumlike-ion 3 d - 3f and 3d - 5f lasers. A small prepulse was introduced to modify the st ate of a silicon plasma column with which the spontaneous-emission amplific ation of lithiumlike silicon ion 3d - 4f and 3d - 5f transitions was observ ed. The prepulse-induced behaviors were quite different for the two lines. These results suggest that the sensitivity of the gain of the 3d-4f laser t o the plasma density and the population of the 3d level tends to reduce the difference in laser gain between the 3d - 4f and 3d - 5f transitions predi cted by standard atomic physics codes. (C) 2000 Optical Society of America [S0740-3224(00)01203-0] OCIS code: 140.7240.