A number of improvements have been made to the Stainless Steel Seya beamline. The most
significant change is the addition of new refocus optics to produce a smaller final image
which is located further from the beamline exit flange. This improvement matches the Seya
beamline to modern angle resolved photoemission experiments.
The previous Seya exit mirror produced a final image only 222 mm (8.75 inches) beyond the
exit valve flange. For many experiments, this was not enough clearance to center the
chamber on the focused image. The former cylindrical exit mirror has been replaced by two
mirrors that provide a smaller focused image at a much larger distance from the beamline
exit flange. The new mirror system, designed by Sherry Crossley of the SRC optics group,
was based on one existing mirror and one new mirror purchased from Acton Research
Corporation of Acton, Massachusetts. The vacuum chambers and mirror holders were designed
by Greg Rogers (SRC engineering) and built in the SRC and PSL shops. The new mirrors were
installed November of 1993, and the mirror alignment was fine-tuned in May. The final image
is now located 835 mm (33 inches) beyond the beamline exit flange, allowing even large
experimental chambers to be centered on the focused image. The focused image now measures
1.5 mm wide by .9 mm high, compared to the former image size of 3 mm by 1 mm.
New filter and diode arrays were also added to the beamline in November. Lithium fluoride
and aluminum filters can now be easily inserted and removed from the beam path. A nickel
mesh and gallium-arsenide-phosphide photodiode are available for monitoring the beamline
The old manually-operated exit valve has been replaced by a pneumatic valve which can be
interlocked to protect the beamline pressure during gas-phase experiments.
Another improvement is the addition of a computer control system to the beamline which
simplifies taking I-zero scans, and allows the user to enter any desired wavelength
position and scan to it easily. The computer will automatically remove the backlash when
scanning down in wavelength, and limit switches prevent scanning beyond the range of the
Significant changes have also been made in the monochromator drive system. The former
stepping motor has been replaced with a new micro stepping motor which allows finer control
of the grating scan. The rotary encoder has been relocated to a more protected location
inside the monochromator housing. Calibrations with the gas cell before and after the
beamline relocation confirm that the scan is linear and accurate to within 1.2% throughout
the scan range. The measured error in energy is not greater than 0.01 eV at 11.62 eV.
The beamline relocation and the installation of the new exit optics were completed in 1993
by Mike Lagergren, Dan Wallace, and Sherry Crossley, all of the SRC optics group, and Greg
Rogers, SRC engineering.