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

Abstract

We present a new optical system that significantly reduces helicity-dependent instrumental intensity asymmetries. It is an extension of a previous scheme [Appl. 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. The two temporally separated beams are then spatially recombined using a second beam splitter. A liquid crystal retarder preceding the first beam splitter controls the relative intensity of the two oppositely polarized beams, allowing reduction of instrumental asymmetries. This system has been modified to include a spatial filter and a Pockels cell placed after the second beam splitter to act as a second active polarization element. Using this method, we can control instrumental asymmetries to ∼5×10(-7) in 1 h of data taking, which is comparable to the precision achieved in "second-generation" high energy electron-nuclear scattering parity violation experiments.

Spin-polarized electron transmission through chiral halocamphor molecules

“…The energy width of the electron beam was ∼0.5 eV, and its polarization was typically ∼30% as measured by an optical polarimeter [18]. To reduce instrumental asymmetries, we made use of the feedback system described in reference [19] which combined a spatial filter and quarterwave plate in the optical setup used for photoemission. The incident electron beam entered the target cell (depicted in figure 3) with the collision energy determined by the voltage applied to the inner target cell.…”

Anomalously Large Chiral Sensitivity in the Dissociative Electron Attachment of 10-Iodocamphor

“…The source of longitudinally spin-polarized electrons is a GaAs photocathode [23]. The optical setup used to produce the circularly polarized light for photoemission also allows for active feedback to reduce instrumental asymmetries [24].…”

“…Data were taken using two orthogonal settings of the quarter-wave plate that circularly polarizes the source laser light, thereby flipping the sign of the electron polarization for a given optical configuration [24]. Uncertainties were determined by taking the quadrature sum of the statistical counting uncertainty (given by the standard deviation of the mean of the measurements at a given energy) and the systematic error (estimated by the magnitude of the sum of the measurements with opposite quarter-wave plate settings).…”

Positron Annihilation Lifetime Analysis of Left- and Right-Handed Alanine Single Crystals

“…A commonly used example in chemistry is that of liquid chromatography where an asymmetric (chiral) column packing material is used to separate asymmetric molecules via the interactions between the packed column and the solution-phase molecule. For a particle example of stereoselection (and stereorecognition) the recent work by Dreiling et al is of great importance [12][13][14]. In these experiments, oppositely polarized electrons selectively interact with one asymmetric form of a selected chiral gasphase molecule.…”

“…This interest extends to the other beta particle, the electron, and polarized electron experiments with asymmetric matter that have been recently appearing in the literature [12][13][14]. Of particular interest were positron annihilation experiments with chiral liquids and their frozen form [5] and experiments with amino acid powders to determine whether positrons could selectively destroy one amino acid enantiomeric form over the other [8][9][10].…”