  SLAC E-158 is an experiment designed to make the first measurement of parity
violation in Moller scattering. E-158 will measure the right-left cross-section
asymmetry, A_LR^Moller, in the elastic scattering of a 45-GeV polarized
electron beam off unpolarized electrons in a liquid hydrogen target. E-158
plans to measure the expected Standard Model asymmetry of ~10^-7 to an accuracy
of better than 10^-8. To make this measurement, the polarized electron source
requires for operation an intense circularly polarized laser beam and the
ability to quickly switch between right- and left-helicity polarization states
with minimal right-left helicity-correlated asymmetries in the resulting beam
parameters (intensity, position, angle, spot size, and energy), ^beam A_LR's.
This laser beam is produced by a unique SLAC-designed flashlamp-pumped
Ti:Sapphire laser and is propagated through a carefully designed set of
polarization optics. We analyze the transport of nearly circularly polarized
light through the optical system and identify several mechanisms that generate
^beam A_LR's. We show that the dominant effects depend linearly on particular
polarization phase shifts in the optical system. We present the laser system
design and a discussion of the suppression and control of ^beam A_LR's. We also
present results on beam performance from engineering and physics runs for
E-158.
