This spectrum was measured by using Si(111) crystal as a monochromator (by courtesy of Dr. Yoda of JASRI).
The detector was a Si PIN diode (Hamamatsu Photonics).
In order to reduce the x-ray intensity, the x-ray beam was chopped with a fast shutter which has a duty ratio of about 0.3%.
The undulator gap was 14.3 mm so that the fundamental radiation had a peak at 12.4 keV.
Spectra at different undulator gaps and with different combinations of mirrors (PDF).
Newer measurements (january 2003).