The results of space-resolved investigations on false amplification observed in soft-x-ray laser experiments that are due to axial plasma expansion are presented. Space-resolved observations show a difference in the spontaneous-emission intensities of the N Balmer-α line for plasmas with different active media lengths, which can be a cause of overestimation of gain coefficients. The deviations of the intensities are found to be small for optically thick lines and for lower pump intensities. Modeling calculations that include the effects of axial expansions are also performed that support the experimental observations. The different N Balmer-α intensity profiles observed for short and long active media lengths are attributed to expansion of the cylindrical plasma in the axial direction, which tends to force plasmas with smaller volumes to expand and cool at an enhanced rate.

© 1996 Optical Society of America.

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