Measurement of the Integrated Stokes Parameters of Zn 468 nm Fluorescence Excited by Polarized-Electron Impact

The integrated Stokes parameters P1, P2, and P3 of Zn (43P0,1 – 53S1) fluorescence resulting from transversely-spin-polarized electron impact excitation of the Zn (4s5s)53S1 state have been measured. This work was motivated by similar studies reported several years ago, in which non-zero values of the integrated Stokes parameter P2 between the threshold for the (4s5s)53S1 excitation and the first cascading (4s5p)53PJ threshold were measured. We observe optical excitation functions in agreement with previous experimental and theoretical results, but find integrated P2 Stokes parameter values which are consistent with zero and inconsistent with those measured previously

Using Earth to Search for Long-Range Spin-Velocity Interactions

Precision measurements of the possible coupling of spin to other scalars, vectors and pseudovectors has proven to be a sensitive way to search for new particle physics beyond the standard model. Indeed, in addition to searching for exotic spin-spin interactions, studies have been undertaken to look for couplings of spin to gravity, the relative velocity between particles, and preferred directions. Several laboratory experiments have established upper bounds on the energy associated with various fermion spin-orientations relative to Earth. Here, we combine these results with a model of Earth in order to investigate the possible long-range spin-velocity interactions associated with the exchange of ultralight ($m_{z'}<1$ neV) or massless scalar or vector bosons. We establish stringent bounds on the strength of these couplings between electrons, neutrons, protons and nucleons.Comment: 6 pages, 1 figure, 1 tabl

Method for monitoring GaAs photocathode heat cleaning temperature

Before a GaAs photocathode can be activated to achieve a negative electron affinity condition, the GaAs crystal must be cleaned. This is most commonly done by ohmic, radiative, or electron bombardment heating. We report a new technique to monitor the temperature of heated GaAs photocathodes by observation with a camera. The method is robust and yields the same temperatures for different GaAs samples heated using different methods in different mounting configurations

Search for spin-polarized photoemission from GaAs using light with orbital angular momentum

Laser light with photon energy near the band gap of GaAs and in Laguerre-Gaussian modes with different amounts of orbital angular momentum was used to produce photoemission from unstrained GaAs. The degree of electron spin polarization was measured using a micro-Mott polarimeter and found to be consistent with zero with an upper limit of ∼3% for light with up to ±5h of orbital angular momentum. In contrast, the degree of spin polarization of 32.3 ± 1.4% using circularly polarized laser light at the as the same wavelength, which is typical for bulk GaAs photocathodes

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]], twophoton photoemission with 1560 nm light was used with photocathodes of varying thickness: 625m, 0.32m, and 0.18m. 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 highly-polarized 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

Measurement of the Integrated Stokes Parameters of Zn 468 nm Fluorescence Excited by Polarized-Electron Impact

The integrated Stokes parameters P1, P2, and P3 of Zn (43P0,1 – 53S1) fluorescence resulting from transversely-spin-polarized electron impact excitation of the Zn (4s5s)53S1 state have been measured. This work was motivated by similar studies reported several years ago, in which non-zero values of the integrated Stokes parameter P2 between the threshold for the (4s5s)53S1 excitation and the first cascading (4s5p)53PJ threshold were measured. We observe optical excitation functions in agreement with previous experimental and theoretical results, but find integrated P2 Stokes parameter values which are consistent with zero and inconsistent with those measured previously

Alignment of the (3\u3ci\u3ed\u3c/i\u3e\u3csup\u3e10\u3c/sup\u3e4\u3ci\u3es\u3c/i\u3e5\u3ci\u3es\u3c/i\u3e)\u3csup\u3e3\u3c/sup\u3e\u3ci\u3eS\u3c/i\u3e\u3csub\u3e1\u3c/sub\u3e State of Zn Excited by Polarized Electron Impact

We measure the integrated Stokes parameters of light from Zn (4s4p)43P0,1-(4s5s)53S1 transitions excited by a transversely polarized electron impact at energies between 7.0 and 8.5 eV. Our results for the electron-polarization-normalized linear polarization Stokes parameter P2, between incident electron energies 7.0 and 7.4 eV, are consistent with zero, as required by basic angular-momentum coupling considerations and by recent theoretical calculations. They are in qualitative disagreement with previous experimental results for the P2 parameter

Alignment of the (3\u3ci\u3ed\u3c/i\u3e\u3csup\u3e10\u3c/sup\u3e4\u3ci\u3es\u3c/i\u3e5\u3ci\u3es\u3c/i\u3e)\u3csup\u3e3\u3c/sup\u3e\u3ci\u3eS\u3c/i\u3e\u3csub\u3e1\u3c/sub\u3e State of Zn Excited by Polarized Electron Impact

We measure the integrated Stokes parameters of light from Zn (4s4p)43P0,1-(4s5s)53S1 transitions excited by a transversely polarized electron impact at energies between 7.0 and 8.5 eV. Our results for the electron-polarization-normalized linear polarization Stokes parameter P2, between incident electron energies 7.0 and 7.4 eV, are consistent with zero, as required by basic angular-momentum coupling considerations and by recent theoretical calculations. They are in qualitative disagreement with previous experimental results for the P2 parameter

Method for monitoring GaAs photocathode heat cleaning temperature

Before a GaAs photocathode can be activated to achieve a negative electron affinity condition, the GaAs crystal must be cleaned. This is most commonly done by ohmic, radiative, or electron bombardment heating. We report a new technique to monitor the temperature of heated GaAs photocathodes by observation with a camera. The method is robust and yields the same temperatures for different GaAs samples heated using different methods in different mounting configurations