Analytical theory of intensity fluctuations in SASE

Recent advances in SASE experiments stimulate interest in quantitative comparison of measurements with theory. Extending our previous analysis (Krinsky and Yu, Phys. Rev. A 35 (8) (1987) 3406) of the SASE intensity in guided modes, we provide an analytical description of the intensity fluctuations by calculating intensity correlation functions in the frequency domain. Comparison of our results with experiment yields new insight into the SASE process.