Development of coherent x ray lasers

Proposed x‐ray laser applications such as interferometry and holography require coherent radiation. The fact that x‐ray laser media are short‐lived high‐temperature plasmas leads to very different coherence properties from those of ordinary lasers. Research aimed at developing theoretical models and experimentally characterizing and improving x‐ray laser coherence is discussed. Longitudinal coherence is already sufficient for several applications due to the narrow linewidths. However, transverse coherence is estimated to be poor for most current x‐ray lasers. To quantify these estimates and to design better lasers, both wave and geometric optics propagation and coherence theories have been developed. These theories and resulting predictions of the coherence length are presented and compared. Measurements of x‐ray laser beam patterns and coherence lengths are presented and compared to detailed theoretical simulations. Designs for more coherent lasers are given.