The excess coincidence rate of hard x rays from a high-brilliance undulator source is considered in two cases. For spontaneously emitted radiation, the predictions of the theory are in agreement with the first definitive experimental results on excess coincidences obtained at the SPring-8 facility in Japan. As the second case, the calculations are extended to applications of coincidence counting techniques with future free-electron lasers at x-ray wavelengths. It is found that two-photon coincidence counting may provide a unique tool for studying the onset of self-amplified spontaneous emission of hard x rays.
© 2004 Optical Society of America
(030.5290) Coherence and statistical optics : Photon statistics
(140.2600) Lasers and laser optics : Free-electron lasers (FELs)
(320.2250) Ultrafast optics : Femtosecond phenomena
(340.7480) X-ray optics : X-rays, soft x-rays, extreme ultraviolet (EUV)
E. Ikonen, "Excess coincidences of spontaneous and stimulated x rays," J. Opt. Soc. Am. B 21, 1403-1407 (2004)