Performance of YB66 double-crystal monochromator for dispersing synchrotron radiation at SPring-8

In the 1–2 keV range, we adopted YB66 crystal for dispersing synchrotron radiation of the beamline No.15 (BL15XU) at SPring-8. YB66 crystal has a large d-value of 0.586 nm for the 4 0 0 reflection and is useful as a soft X-ray monochromator for dispersing synchrotron radiation, since there is no intrinsic absorption edge and it is more resistant than other crystals to synchrotron radiation damage. We investigated the resolution of the YB66 double-crystal monochromator and measured the photon flux passing through this monochromator. The full-width at half-maximum of the rocking curve ranged from 0.15 eV at 1.1 keV to 0.42 eV at 2.1 keV. The photon flux ranged from 6×108 photons/sec/100 mA measured at an experimental position at 1.1 keV to 5×109 photons/sec/100 mA measured at an experimental position at 2 keV. It is considered that the better energy resolution of the YB66 crystal was achieved by irradiating only a small restricted area of the crystal by an incident beam with small angular divergence originated from a helical undulator.