Active feedback scheme for minimization of helicity-dependent instrumental asymmetries

Abstract

Fabrikant, M. I.; Trantham, K. W.; Andrianarijaona, V. M.; and Gay, Timothy J., "Active feedback scheme for minimization of helicitydependent instrumental asymmetries" (2008). Timothy J. Gay Publications. 57.

New technique for the reduction of helicity-correlated instrumental asymmetries in photoemitted beams of spin-polarized electrons

“…As long as it is constant, however, any resultant nonzero value of A T can be subtracted from an experimental "physics" asymmetry, as previously mentioned. This optical arrangement (as well as our earlier one [12]) solves the problem of using an electro-optic element-which will invariably produce spatial variations-as both the active feedback and the helicity-flipping component.…”

“…In 2008, our group employed an active-feedback scheme to control the standard deviation of the mean (SDM) of A S as measured by a photodiode to 2 × 10 −6 [12]. That work was based on a simple feedback scheme that relied on the digitized response of the photodiode to the laser beam whose helicity was flipped by a combination of chopper and beam-splitting cubes.…”

“…Opt. 47, 2465(2008], where one laser beam is split using a polarizing beam splitter into two with orthogonal linear polarizations. The beams are sent through a chopper, allowing only one to pass at a time.…”

Reduction of electron photocurrent asymmetries by active feedback

“…The electron beam of alternating polarization is produced by illuminating a GaAs crystal with a 785 nm laser beam of alternating helicity. The optical system is discussed in further detail in [2] and shown in Figure 1. Instrumental asymmetries arise if the two polarizations of electrons result in different currents as measured on an electron-optical element in the apparatus.…”