An improved source of spin-polarized electrons based on spin exchange in optically pumped rubidium vapor.

We have improved a polarized electron source in which unpolarized electrons undergo collisions with a mixture of buffer gas molecules and optically spin-polarized Rb atoms. With a nitrogen buffer gas, the source reliably provides spin polarization between 15% and 25% with beam currents >4 μA. Vacuum pump upgrades mitigate problems caused by denatured diffusion pump oil, leading to longer run times.

A simple, isotropic depolarized light source.

Unpolarized light can be an important tool in optical experiments. Producing it, however, can prove to be a challenge. Natural sources of light that are commonly thought of as unpolarized are, in fact, either weakly polarized or not practical sources of light in a laboratory setting.

A search for chiral asymmetry in secondary electron emission from cysteine induced by longitudinally polarized electrons.

We performed experiments searching for chirality-dependent secondary electron emission for a 141 eV longitudinally spin-polarized electron beam incident on a thick solid cysteine target. We determined the secondary electron yield by measuring the positive current produced when the cysteine target was negatively biased. No spin-dependent effects to a level of 10-3 were found for the secondary electron emission yield.

Non-Poissonian Ultrashort Nanoscale Electron Pulses.

The statistical character of electron beams used in current technologies, as described by a stream of particles, is random in nature. Using coincidence measurements of femtosecond pulsed electron pairs, we report the observation of sub-Poissonian electron statistics that are nonrandom due to two-electron Coulomb interactions, and that exhibit an antibunching signal of 1 part in 4. This advancement is a fundamental step toward observing a strongly quantum degenerate electron beam needed for many applications, and in particular electron correlation spectroscopy.

Helmholtz spacing of thin rectangular magnetic field coils.

In this Note, we discuss the Helmholtz spacing for a pair of thin rectangular coils of arbitrary aspect ratio and consider how best to use such coils to compensate for Earth's magnetic field along the coils' Cartesian symmetry axes. Such coils are frequently used in conjunction with charged-particle beam machines. The Helmholtz spacing varies non-monotonically between that for square coils and that for four optimally spaced infinite wires.

Demonstration of vacuum strain effects on a light-collection lens used in optical polarimetry.

The precision by which an electron spin polarization measurement can be made using a noble-gas polarimeter depends directly on the accuracy of a light-polarization measurement. Since the electron-noble gas collisions occur in a vacuum chamber and the optical polarimeter is generally outside the chamber, this work examines the effect the vacuum window has on the perceived optical polarization. A model light source, lens system, and optical polarimeter are used that approximate the situation found in a typical atomic physics experiment.

Alignment of the (3d^{10}4s5s)^{3}S_{1} State of Zn Excited by Polarized Electron Impact.

We measure the integrated Stokes parameters of light from Zn (4s4p)4^{3}P_{0,1}-(4s5s)5^{3}S_{1} transitions excited by a transversely polarized electron impact at energies between 7.0 and 8.5 eV.

A cylindrically symmetric "micro-Mott" electron polarimeter.

A small, novel, cylindrically symmetric Mott electron polarimeter is described. The effective Sherman function, Seff, or analyzing power, for 20 kV Au target bias with a 1.3 keV energy loss window is 0.

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

We have studied dissociative electron attachment (DEA) between low energy (≤0.6  eV) longitudinally polarized electrons and gas-phase chiral targets of 3-bromocamphor (C_{10}H_{15}BrO), 3-iodocamphor (C_{10}H_{15}IO), and 10-iodocamphor. The DEA rate depends on the sign of the incident electron helicity for a given target handedness, and it varies with both the atomic number (Z) and location of the heaviest atom in the molecule.

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

We present a new optical system that significantly reduces helicity-dependent instrumental intensity asymmetries. It is an extension of a previous scheme [Appl. Opt.

Chirally sensitive electron-induced molecular breakup and the Vester-Ulbricht hypothesis.

We have studied dissociative electron attachment in sub-eV collisions between longitudinally polarized electrons and chiral bromocamphor molecules. For a given target enantiomer, the dissociative Br anion production depends on the helicity of the incident electrons, with an asymmetry that depends on the electron energy and is of order 3×10^{-4}. The existence of chiral sensitivity in a well-defined molecular breakup reaction demonstrates the viability of the Vester-Ulbrict hypothesis, namely, that the longitudinal polarization of cosmic beta radiation was responsible for the origins of biological homochirality.

Threshold alignment reversal and circularly polarized fluorescence in rotationally resolved H2.

Using H2 and D2 targets, we have measured the polarization of Fulcher-band fluorescence resulting from spin-polarized electron-impact excitation of vibrationally and rotationally resolved d 3Π(u) → a 3Σ(g)+ transitions for incident electron energies from 14.3 to 28.5 eV.

Compact inline optical electron polarimeter.

A compact optical electron polarimeter using a helium target is described. It offers a maximum fluorescence detection efficiency of ~20 Hz/nA, which is an order of magnitude higher than that of earlier designs. With an argon target, this device is expected to have a polarimetric figure-of-merit of 270 Hz/nA.

Active feedback scheme for minimization of helicity-dependent instrumental asymmetries.

A method for the active feedback reduction of optical instrumental intensity asymmetries is presented. It is based on the fast chopping of two spatially separated beams of light with orthogonal linear polarizations that are recombined and passed through a quarter-wave plate to yield a single beam with rapidly flipping helicity. Active electro-optic feedback has been successfully employed to maintain this asymmetry below 10(-5).

Assignments of normally unoccupied orbitals to the temporary negative ion states of several lanthanide NMR shift reagents and comments on resonance involvement in electron circular dichroism.

We have measured the total electron scattering cross sections of several NMR shift reagent molecules X(hfc)3, where X = Yb, Er, Eu and Pr, by means of electron transmission spectroscopy (ETS) to determine their vertical attachment energies. A strong low-energy resonance (<1 eV) is observed in all of the compounds except for Yb(hfc)3. We explain this anomaly in terms of the ground-state electron configuration of each molecule.

Spin-exchange-induced circularly polarized molecular fluorescence.

We have measured the circular polarization of light emitted from both atomic H and molecular H2 after bombarding H2 with longitudinally polarized electrons. For both atomic and molecular fluorescence near threshold we observe a circular polarization as great as 10% of the electron polarization. This represents the first direct observation of spin transfer in electron-molecule collisions.

Effect of relativistic many-electron interactions on photoelectron partial wave probabilities.

We obtain relative cross sections for the production of photoelectrons with specific angular momentum quantum numbers. These cross sections are obtained from the polarization analysis of the visible fluorescence of ions produced when circularly polarized vacuum ultraviolet radiation photoionizes ground state Ar. The ratio of cross sections for the production of photoelectrons with the same orbital angular momentum but different total angular momenta shows strong deviations from the statistical ratio, demonstrating the importance of relativistic interactions in many-electron photoionization dynamics.

Quantum-mechanical analysis of a longitudinal Stern-Gerlach effect.

We present the results of a rigorous quantum-mechanical calculation of the propagation of electrons through an inhomogeneous magnetic field with axial symmetry. A complete spin polarization of the beam is demonstrated assuming that a Landau eigenstate can be inserted into the field. This is in contrast with the semiclassical situation, where the spin splitting is blurred.

Angular momentum partitioning and hexacontatetrapole moments in impulsively excited argon ions.

We have studied polarized electron collisions with Ar in which the target is simultaneously ionized and excited to form Ar+(3p(4)(1D)4p) states. We measured the integrated Stokes parameters of the subsequent fluorescence emitted by the (2)F(7/2), (2)F(5/2), (2)D(5/2), and (2)P(3/2) states along the direction of electron polarization. The Rubin-Bederson hypothesis is shown to hold for the L and S multipoles of these states.