Soft x-ray laser optics

The optics of exploding foil soft x-ray lasers is discussed, including both refraction within the lasing plasma and reflection by multi-layer mirrors placed beyond the plasma. The effect of refraction on amplification and on the angular beam pattern for single pass amplifiers is described. The effect of refractive propagation on the performance of multi-pass cavities is also discussed. Within the plasma, refraction due to electron density gradients tends to direct the x rays out of high density regions. This usually has the undesirable effect of shortening the distance that the x rays stay within the plasma, thereby limiting the amount of amplification. A quantitative analysis of the propagation and amplification in an exploding foil x-ray laser is presented. It is found that refraction introduces a loss term to the laser amplification. Multi-layer mirrors have been used to increase the efficiency and quality of x-ray lasers by setting up two-pass or multi-pass amplifier cavities. The theoretical considerations impacting the curvature and placement of mirrors is discussed. The analysis of time resolved spectral data from experiments using normal incidence multi-layer mirrors is also discussed, in the context of gain and refraction models