THE LBL 55-METER SPHERICAL GRATING MONOCHROMATOR AT SSRL

A 55 meter spherical grating monochromator has been completed at the Stanford Synchrotron Radiation Laboratory (SSRL). The monochromator includes a unique capability for water cooled gratings, and is presently operating with a fused silica grating from 180 to 820 eV. A resolution of 60 meV has been achieved at 400 eV, inferred from the linewidths of the nitrogen 1s-π* resonance. A photon flux of 4 × 1010 photon/s has been observed at 440 eV and 40 mA ring current (and with 0.5 eV resolution). It is expected that this flux value will improve by a factor of approximately 10-30 when a full-performance condensing system is installed later this year. The optical and mechanical systems design of the Rowland Circle monochromator with moving entrance and exit slits is reviewed. The details of the laser interferometer encoded wavelength drive, the mounting of the water cooled gratings, and the mechanical design features which improve the stability and accuracy of the system are described. The alignment of the gratings, grating chamber, and slits is discussed. © 1990.