Joan Dreiling

Anomalously Large Chiral Sensitivity in theDissociative 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. While simple dynamic mechanisms can account for the asymmetry dependence on Z, they fail to explain the large asymmetry variation with the heavy atom location.

Electron-spin-reversal phenomenon in optically pumped rubidium

We have studied the optical pumping of mixtures of Rb vapor and N{sub 2} buffer gas by laser light tuned to the D{sub 1} transition having a spectral width of {approx}500 MHz. The Rb densities are of the order of 10{sup 13} cm{sup -3}, while the buffer-gas pressures range from 0.1 to 10 torr. As the frequency of the right-hand circularly polarized laser is varied across the D{sub 1} absorption profile, the electron spin polarization of the Rb is found to take on negative values for small negative values of pump detuning from the absorption profile center. This occurs for N{sub 2} pressures below {approx}1 torr; at 10 torr the electron spins consistently point in the same direction as the angular momentum of the pump light. The spin-reversal effect can be understood in terms of populations of the F=2 ({sup 85}Rb) and F=1 ({sup 87}Rb) states caused by small unpolarized fractions in the pump beam and its elimination in terms of pressure broadening caused by the N{sub 2} buffer gas. We speculate that this effect could be used for fast Rb spin modulation.

Two Novel Approaches for Electron Beam Polarization from Unstrained GaAs

Two novel approaches to producing highly-polarized electron beams from unstrained GaAs were tested using a micro-Mott polarimeter. Based on a suggestion by Nakanishi [1], two-photon photoemission with 1560 nm light was used with photocathodes of varying thickness: 625m, 0.32m, and 0.18m. For each of these photocathodes, the degree of spin polarization of the photoemitted beam was less than 50%. Polarization via two-photon absorption was highest from the thinnest photocathode sample and close to that obtained from one-photon absorption (using 778 nm light), with values 40.3±1.0% and 42.6±1.0%, respectively. The second attempt to produce highlypolarized electrons used one-photon emission with 778 nm light in Laguerre-Gaussian modes with different amounts of orbital angular momentum. The degree of electron spin polarization was consistent with zero, with an upper limit of ~3% for light with up to ±5ħ of orbital angular momentum. In contrast, the degree of spin polarization was 32.3±1.4% using circularly-polarized laser light at the same wavelength, which is typical for thick, unstrained GaAs photocathodes. [1] T. Matsuyama et al. in Proceedings of the 4 th Pacific Rim Conf. on Lasers and Electro-Optics 164-5 (2001)